Move code to relevant files for organization

5 files changed, 1212 insertions, 1181 deletions

diff --git a/src/bitmap.h b/src/bitmap.h
new file mode 100644
index 0000000..0befe5d
--- /dev/null
+++ b/src/bitmap.h
@@ -0,0 +1,228 @@
+#ifndef GBAEXP_BITMAP_H
+#define GBAEXP_BITMAP_H
+
+#include "bd-font.c"
+#include "common.c"
+
+// Using bd-font, an 8x8 bitmap font.
+static void
+put_char(int x, int y, Color clr, u8 chr) {
+    for (size_t i = 0; i < 8; ++i) {
+        for (size_t j = 0; j < 8; ++j) {
+            if ((font[chr][i] >> (7 - j)) & 0x1) {
+                FRAMEBUFFER[y + i][x + j] = clr;
+            }
+        }
+    }
+}
+
+static void
+put_text(int x, int y, Color clr, char *msg) {
+    int count = 0;
+    while (*msg) {
+        put_char(x + count, y, clr, *msg++);
+        count += 8;
+    }
+}
+
+// Draws a line with the given color between (x0,y0) and (x1,y1) using the
+// Bresenham's line drawing algorithm using exclusively integer arithmetic.
+static void
+draw_line(int x0, int y0, int x1, int y1, Color clr) {
+    // Pointer to the initial position of the screen buffer where we will start
+    // writing our data.
+    vu16 *destination = (u16*)(SCREEN_BUFFER + y0 * SCREEN_WIDTH + x0);
+
+    // Adjust the step direction and calculate deltas.
+    int x_step;
+    int y_step;
+    int dx;
+    int dy;
+    if (x0 > x1) {
+        x_step = -1;
+        dx = x0 - x1;
+    } else {
+        x_step = 1;
+        dx = x1 - x0;
+    }
+    if (y0 > y1) {
+        y_step = -SCREEN_WIDTH;
+        dy = y0 - y1;
+    } else {
+        y_step = +SCREEN_WIDTH;
+        dy = y1 - y0;
+    }
+
+    if(dy == 0) {
+        // Horizontal line.
+        for(int i = 0; i <= dx; i++) {
+            destination[i * x_step] = clr;
+        }
+    } else if(dx == 0) {
+        // Vertical line.
+        for(int i = 0; i <= dy; i++) {
+            destination[i * y_step] = clr;
+        }
+    } else if (dx >= dy){
+        // Positive slope.
+        int diff = 2 * dy - dx;
+        for (int i = 0; i <= dx; ++i) {
+            *destination = clr;
+            if (diff >= 0) {
+                destination += y_step;
+                diff -= 2 * dx;
+            }
+            destination += x_step;
+            diff += 2 * dy;
+        }
+    } else {
+        // Negative slope.
+        int diff = 2 * dx - dy;
+        for (int i = 0; i <= dy; ++i) {
+            *destination = clr;
+            if (diff >= 0) {
+                destination += x_step;
+                diff -= 2 * dy;
+            }
+            destination += y_step;
+            diff += 2 * dx;
+        }
+    }
+}
+
+static inline void
+draw_rect(int x0, int y0, int x1, int y1, Color clr) {
+    if (x0 > x1) {
+        int tmp = x0;
+        x0 = x1;
+        x1 = tmp;
+    }
+    if (y0 > y1) {
+        int tmp = y0;
+        y0 = y1;
+        y1 = tmp;
+    }
+    int dx = x1 - x0;
+    int dy = y1 - y0;
+    for (int i = 0; i <= dx; ++i) {
+        int x = x0 + i;
+        FRAMEBUFFER[y0][x] = clr;
+        FRAMEBUFFER[y1][x] = clr;
+    }
+    for (int j = 0; j <= dy; ++j) {
+        int y = y0 + j;
+        FRAMEBUFFER[y][x0] = clr;
+        FRAMEBUFFER[y][x1] = clr;
+    }
+}
+
+static inline void
+draw_fill_rect(int x0, int y0, int x1, int y1, Color clr) {
+    if (x0 > x1) {
+        int tmp = x0;
+        x0 = x1;
+        x1 = tmp;
+    }
+    if (y0 > y1) {
+        int tmp = y0;
+        y0 = y1;
+        y1 = tmp;
+    }
+    int dx = x1 - x0;
+    int dy = y1 - y0;
+    for (int i = 0; i <= dx; ++i) {
+        for (int j = 0; j <= dy; ++j) {
+            int x = x0 + i;
+            int y = y0 + j;
+            FRAMEBUFFER[y][x] = clr;
+        }
+    }
+}
+
+// In Mode4 the buffer is of 8 bytes per pixel instead of 16. We can't write the
+// color directly, instead the color is stored in the palette memory at
+// `MEM_PAL`. Note that in this mode MEM_PAL[0] is the background color. This
+// plotter takes an index to a color stored in MEM_PAL[col_index]. Because the
+// GBA needs to meet memory alignment requirements, we can't write a u8 into
+// memory, instead we need to read a u16 word, mask and or the corresponding
+// bits and wave the updated u16.
+static void
+put_pixel_m4(int x, int y, u8 col_index, vu16 *buffer) {
+    int buffer_index = (y * SCREEN_WIDTH + x) / 2;
+    vu16 *destination = &buffer[buffer_index];
+    // Odd pixels will go to the top 8 bits of the destination. Even pixels to
+    // the lower 8 bits.
+    int odd = x & 0x1;
+    if(odd) {
+        *destination= (*destination & 0xFF) | (col_index << 8);
+    } else {
+        *destination= (*destination & ~0xFF) |  col_index;
+    }
+}
+
+static void
+draw_fill_rect_m4(int x0, int y0, int x1, int y1, u8 col_index, vu16 *buffer) {
+    int ix, iy;
+    for(iy = y0; iy < y1; iy++) {
+        for(ix = x0; ix < x1; ix++) {
+            put_pixel_m4(ix, iy, col_index, buffer);
+        }
+    }
+}
+
+void
+draw_logo(void) {
+    int side = 60;
+    int line = 35;
+    int height = side * 0.5;
+    int x = SCREEN_WIDTH / 2 - height / 2;
+    int y = SCREEN_HEIGHT / 2;
+
+    // Draw red triangle.
+    draw_line(x + height - 1, y - side / 2, x, y - 1, COLOR_RED);
+    draw_line(x + height - 1, y + side / 2, x, y + 1, COLOR_RED);
+    draw_line(x + height - 1, y - side / 2 + 1, x, y, COLOR_RED);
+    draw_line(x + height - 1, y + side / 2 - 1, x, y, COLOR_RED);
+
+    // Draw white triangle.
+    draw_line(x, y - side / 2, x, y + side / 2, COLOR_WHITE);
+    draw_line(x + 1, y - side / 2, x + height, y - 1, COLOR_WHITE);
+    draw_line(x + 1, y + side / 2, x + height, y + 1, COLOR_WHITE);
+
+    // Draw white line at triangle tip.
+    draw_line(x + height, y - side / 2, x + height, y + side / 2, COLOR_WHITE);
+    draw_line(x + height + 1, y - side / 2, x + height + 1, y + side / 2, COLOR_WHITE);
+
+    // Double triangle line.
+    draw_line(x - 1, y - side / 2, x - 1, y + side / 2, COLOR_WHITE);
+    draw_line(x + 1, y - side / 2 + 1, x + height, y, COLOR_WHITE);
+    draw_line(x + 1, y + side / 2 - 1, x + height, y, COLOR_WHITE);
+
+    // Draw white lines.
+    draw_line(x - line, y, x, y, COLOR_WHITE);
+    draw_line(x + height, y, x + height + line, y, COLOR_WHITE);
+    draw_line(x - line, y + 1, x, y + 1, COLOR_WHITE);
+    draw_line(x + height, y + 1, x + height + line, y + 1, COLOR_WHITE);
+}
+
+void
+copy_font_to_tile_memory(Tile *tile) {
+    // Hex to bits translation table.
+    const u32 conversion_u32[16] = {
+        0x00000000, 0x00001000, 0x00000100, 0x00001100,
+        0x00000010, 0x00001010, 0x00000110, 0x00001110,
+        0x00000001, 0x00001001, 0x00000101, 0x00001101,
+        0x00000011, 0x00001011, 0x00000111, 0x00001111,
+    };
+    for (size_t i = 0; i < 250; ++i) {
+        for (size_t j = 0; j < 8; ++j) {
+            u8 row = font[i][j];
+            u32 tile_idx = 0x00000000;
+            tile_idx = conversion_u32[row & 0xF] << 16;
+            tile_idx |= conversion_u32[(row >> 4) & 0xF];
+            (tile + i)->data[j] = tile_idx;
+        }
+    }
+}
+
+#endif // GBAEXP_BITMAP_H
diff --git a/src/common.h b/src/common.h
new file mode 100644
index 0000000..35b4619
--- /dev/null
+++ b/src/common.h
@@ -0,0 +1,281 @@
+#ifndef GBAEXP_COMMON_H
+#define GBAEXP_COMMON_H
+
+#include "shorthand.h"
+
+//
+// Memory sections.
+//
+
+// Defines for the different memory sections in the GBA.
+#define MEM_SROM  0x00000000
+#define MEM_EW    0x02000000
+#define MEM_IW    0x03000000
+#define MEM_IO    0x04000000
+#define MEM_PAL   0x05000000
+#define MEM_VRAM  0x06000000
+#define MEM_OAM   0x07000000
+#define MEM_PAK   0x08000000
+#define MEM_CART  0x0E000000
+
+//
+// Display modes.
+//
+
+// Display registers.
+#define DISP_CTRL   *((vu32*)(MEM_IO + 0x0000))
+#define DISP_STATUS *((vu16*)(MEM_IO + 0x0004))
+#define DISP_VCOUNT *((vu16*)(MEM_IO + 0x0006))
+
+// The first three bits in the DISP_CTRL are used to control the video mode.
+#define DISP_MODE_0     0x0000
+#define DISP_MODE_1     0x0001
+#define DISP_MODE_2     0x0002
+#define DISP_MODE_3     0x0003
+#define DISP_MODE_4     0x0004
+#define DISP_MODE_5     0x0005
+#define DISP_GB         (1 << 3)
+#define DISP_PAGE       (1 << 4)
+#define DISP_OAM_HBLANK (1 << 5)
+#define DISP_OBJ_1D     (1 << 6)
+#define DISP_BLANK      (1 << 7)
+#define DISP_BG_0       (1 << 8)
+#define DISP_BG_1       (1 << 9)
+#define DISP_BG_2       (1 << 10)
+#define DISP_BG_3       (1 << 11)
+#define DISP_OBJ        (1 << 12)
+#define DISP_ENABLE_SPRITES DISP_OBJ | DISP_OBJ_1D
+
+// Registers to control of BG layers.
+#define BG_CTRL_0 *((vu16*)(0x04000008 + 0x0002 * 0))
+#define BG_CTRL_1 *((vu16*)(0x04000008 + 0x0002 * 1))
+#define BG_CTRL_2 *((vu16*)(0x04000008 + 0x0002 * 2))
+#define BG_CTRL_3 *((vu16*)(0x04000008 + 0x0002 * 3))
+
+// Bits to control the background.
+#define BG_PRIORITY_0     0x0
+#define BG_PRIORITY_1     0x1
+#define BG_PRIORITY_2     0x2
+#define BG_PRIORITY_3     0x3
+#define BG_CHARBLOCK(N)   ((N) << 2)
+#define BG_MOSAIC         (1 << 6)
+#define BG_HIGH_COLOR     (1 << 7)
+#define BG_SCREENBLOCK(N) ((N) << 8)
+#define BG_AFFINE         (1 << 0xD)
+#define BG_SIZE(N)        ((N) << 0xE)
+
+// BG registers for horizontal displacement.
+#define BG_H_SCROLL_0 *((vu16*)(0x04000010 + 0x0004 * 0))
+#define BG_H_SCROLL_1 *((vu16*)(0x04000010 + 0x0004 * 1))
+#define BG_H_SCROLL_2 *((vu16*)(0x04000010 + 0x0004 * 2))
+#define BG_H_SCROLL_3 *((vu16*)(0x04000010 + 0x0004 * 3))
+
+// BG registers for vertical displacement.
+#define BG_V_SCROLL_0 *((vu16*)(0x04000012 + 0x0004 * 0))
+#define BG_V_SCROLL_1 *((vu16*)(0x04000012 + 0x0004 * 1))
+#define BG_V_SCROLL_2 *((vu16*)(0x04000012 + 0x0004 * 2))
+#define BG_V_SCROLL_3 *((vu16*)(0x04000012 + 0x0004 * 3))
+
+// Screen settings.
+#define SCREEN_WIDTH 240
+#define SCREEN_HEIGHT 160
+
+// The GBA in mode 3 expects rbg15 colors in the VRAM, where each component
+// (RGB) have a 0--31 range. For example, pure red would be rgb15(31, 0, 0).
+typedef u16 Color;
+
+//
+// Tile memory access.
+//
+
+// NOTE: Only defining 4bpp tiles for now.
+typedef struct Tile {
+    u32 data[8];
+} Tile;
+
+typedef Tile TileBlock[512];
+#define TILE_MEM ((TileBlock*) MEM_VRAM)
+
+typedef u16 ScreenBlock[1024];
+#define SCREENBLOCK_MEM ((ScreenBlock*)MEM_VRAM)
+
+// We can treat the screen as a HxW matrix. With the following macro we can
+// write a pixel to the screen at the (x, y) position using:
+//
+//     FRAMEBUFFER[y][x] = color;
+//
+typedef Color Scanline[SCREEN_WIDTH];
+#define FRAMEBUFFER        ((Scanline*)MEM_VRAM)
+#define SCREEN_BUFFER      ((u16*) MEM_VRAM)
+#define PAL_BUFFER_BG      ((u16*) MEM_PAL)
+#define PAL_BUFFER_SPRITES ((u16*) 0x05000200)
+
+//
+// Colors.
+//
+
+static inline Color
+rgb15(u32 red, u32 green, u32 blue ) {
+    return (blue << 10) | (green << 5) | red;
+}
+
+#define COLOR_RED   rgb15(31, 0, 12)
+#define COLOR_BLUE  rgb15(2, 15, 30)
+#define COLOR_CYAN  rgb15(0, 30, 30)
+#define COLOR_GREY  rgb15(4, 4, 4)
+#define COLOR_BLACK rgb15(0, 0, 0)
+#define COLOR_WHITE rgb15(28, 28, 28)
+
+//
+// Sprites.
+//
+
+// Using macros instead of aligned structs for setting up OBJ attributes and
+// affine parameters.
+// TODO: Benchmark if this would be slower or the same that TONC's
+// implementation.
+#define OBJ_ATTR_0(N)    *((vu16*)(MEM_OAM + 0 + 8 * (N)))
+#define OBJ_ATTR_1(N)    *((vu16*)(MEM_OAM + 2 + 8 * (N)))
+#define OBJ_ATTR_2(N)    *((vu16*)(MEM_OAM + 4 + 8 * (N)))
+#define OBJ_AFFINE_PA(N) *((vs16*)(MEM_OAM + 6 + 8 * 0 + 8 * 4 * (N)))
+#define OBJ_AFFINE_PB(N) *((vs16*)(MEM_OAM + 6 + 8 * 1 + 8 * 4 * (N)))
+#define OBJ_AFFINE_PC(N) *((vs16*)(MEM_OAM + 6 + 8 * 2 + 8 * 4 * (N)))
+#define OBJ_AFFINE_PD(N) *((vs16*)(MEM_OAM + 6 + 8 * 3 + 8 * 4 * (N)))
+
+// OBJ_ATTR_0 parameters
+#define OBJ_Y_COORD(N)   ((N) & 0xFF)
+#define OBJ_NORMAL       (0x00 << 0x8)
+#define OBJ_AFFINE       (0x01 << 0x8)
+#define OBJ_HIDDEN       (0x02 << 0x8)
+#define OBJ_AFFINE_2X    (0x03 << 0x8)
+#define OBJ_ALPHA_BLEND  (0x01 << 0xA)
+#define OBJ_WINDOW       (0x02 << 0xA)
+#define OBJ_SHAPE_SQUARE (0x00 << 0xE)
+#define OBJ_SHAPE_WIDE   (0x01 << 0xE)
+#define OBJ_SHAPE_TALL   (0x02 << 0xE)
+
+// OBJ_ATTR_1 parameters
+#define OBJ_X_COORD(N)    ((N) & 0x1FF)
+#define OBJ_AFFINE_IDX(N) ((N) << 0x9)
+#define OBJ_H_FLIP        (0x01 << 0xC)
+#define OBJ_V_FLIP        (0x01 << 0xD)
+#define OBJ_SIZE_SMALL    (0x00 << 0xE)
+#define OBJ_SIZE_MID      (0x01 << 0xE)
+#define OBJ_SIZE_BIG      (0x02 << 0xE)
+#define OBJ_SIZE_HUGE     (0x03 << 0xE)
+
+// OBJ_ATTR_2 parameters
+#define OBJ_TILE_INDEX(N) ((N) & 0x3FF)
+#define OBJ_PRIORITY(N)   ((N) << 0xA)
+#define OBJ_PAL_BANK(N)   ((N) << 0xC)
+
+static inline void
+wait_vsync(void) {
+    while(DISP_VCOUNT >= 160);
+    while(DISP_VCOUNT < 160);
+}
+
+//
+// Mode 4 page flipping
+//
+
+static inline void
+flip_page(void) {
+    DISP_CTRL ^= DISP_PAGE;
+}
+
+#define SCREEN_PAGE_1 ((vu16*) MEM_VRAM)
+#define SCREEN_PAGE_2 ((vu16*) (MEM_VRAM + 0xa000))
+
+//
+// Profiling.
+//
+
+#define TIMER_DATA_0  *((vu16*) (0x04000100 + 0x04 * 0))
+#define TIMER_DATA_1  *((vu16*) (0x04000100 + 0x04 * 1))
+#define TIMER_DATA_2  *((vu16*) (0x04000100 + 0x04 * 2))
+#define TIMER_DATA_3  *((vu16*) (0x04000100 + 0x04 * 3))
+#define TIMER_CTRL_0  *((vu16*) (0x04000102 + 0x04 * 0))
+#define TIMER_CTRL_1  *((vu16*) (0x04000102 + 0x04 * 1))
+#define TIMER_CTRL_2  *((vu16*) (0x04000102 + 0x04 * 2))
+#define TIMER_CTRL_3  *((vu16*) (0x04000102 + 0x04 * 3))
+
+// Timer control bits.
+#define TIMER_CTRL_FREQ_0   0
+#define TIMER_CTRL_FREQ_1   1
+#define TIMER_CTRL_FREQ_2   2
+#define TIMER_CTRL_FREQ_3   3
+#define TIMER_CTRL_CASCADE (1 << 2)
+#define TIMER_CTRL_IRQ     (1 << 6)
+#define TIMER_CTRL_ENABLE  (1 << 7)
+
+// We use timers 2 and 3 to count the number of cycles since the profile_start
+// functions is called. Don't use if the code we are trying to profile make use
+// of these timers.
+static inline
+void profile_start(void) {
+    TIMER_DATA_2 = 0;
+    TIMER_DATA_3 = 0;
+    TIMER_CTRL_2 = 0;
+    TIMER_CTRL_3 = 0;
+    TIMER_CTRL_3 = TIMER_CTRL_ENABLE | TIMER_CTRL_CASCADE;
+    TIMER_CTRL_2 = TIMER_CTRL_ENABLE;
+}
+
+static inline
+u32 profile_stop(void) {
+   TIMER_CTRL_2 = 0;
+   return (TIMER_DATA_3 << 16) | TIMER_DATA_2;
+}
+
+//
+// Input handling.
+//
+
+// Memory address for key input register
+#define KEY_INPUTS *((vu16*) 0x04000130)
+
+// Alias for key pressing bits.
+#define KEY_A      (1 << 0)
+#define KEY_B      (1 << 1)
+#define KEY_SELECT (1 << 2)
+#define KEY_START  (1 << 3)
+#define KEY_RIGHT  (1 << 4)
+#define KEY_LEFT   (1 << 5)
+#define KEY_UP     (1 << 6)
+#define KEY_DOWN   (1 << 7)
+#define KEY_R      (1 << 8)
+#define KEY_L      (1 << 9)
+
+#define KEY_MASK 0x03FF
+
+// Saving the previous and current key states as globals for now.
+static u16 key_curr = 0;
+static u16 key_prev = 0;
+
+static inline void
+poll_keys(void) {
+    key_prev = key_curr;
+    key_curr = ~KEY_INPUTS & KEY_MASK;
+}
+
+// Returns true if the given key has been pressed at time of calling and was not
+// pressed since the previous call. For example, if a key is being held, this
+// function will return `true` only on the frame where the key initially
+// activated.
+static inline u32
+key_pressed(u32 key) {
+    return (key_curr & key) & ~(key_prev & key);
+}
+
+// Check if the given key is pressed and has been since at least one frame.
+static inline u32
+key_hold(u32 key) {
+    return (key_curr & key) & key_prev & key;
+}
+
+// Check if the given key/button is currently pressed.
+#define KEY_PRESSED(key) (~(KEY_INPUTS) & key)
+
+
+#endif // GBAEXP_COMMON_H
diff --git a/src/gba-buttons.c b/src/gba-buttons.c
index 951b4dc..dd06351 100644
--- a/src/gba-buttons.c
+++ b/src/gba-buttons.c
@@ -1,3 +1,6 @@
+#include "common.h"
+#include "sprites.h"
+
 // 1bpp packed
 u32 gba_btn_a_data[] = {
     0xc0300804, 0x844242c2, 0x030c1020, 0x21424243,
@@ -133,11 +136,6 @@ u32 gba_btn_fx_startselect[] = {
     0x01800000, 0x00000000, 0x00000000, 0x00000004,
 };
 
-typedef struct SpriteAnimation {
-    size_t *tile_offsets;
-    size_t n_frames;
-} SpriteAnimation;
-
 typedef enum {BTN_STATE_IDLE, BTN_STATE_PRESSED, BTN_STATE_RELEASED, BTN_STATE_HOLD} BtnState;
 
 typedef struct AnimationEntry {
@@ -262,3 +260,597 @@ AnimationEntry *btn_animation_startselect[] = {
         {0, 0, 12, 1},
     },
 };
+
+typedef struct ButtonSprite {
+    ObjState *sprites;
+    AnimationEntry **animations;
+    size_t frame;
+    size_t n_obj;
+    size_t n_frames;
+    BtnState state;
+} ButtonSprite;
+
+void
+init_button_sprite(ButtonSprite *btn) {
+    for (size_t i = 0; i < btn->n_obj; ++i) {
+        btn->sprites[i].id = load_packed_sprite_data(
+                btn->sprites[i].data,
+                btn->sprites[i].n_tiles,
+                btn->sprites[i].frames);
+        btn->sprites[i].base_tile = sprites[btn->sprites[i].id].tile_start;
+    }
+}
+
+void
+button_tick(ButtonSprite *btn) {
+    // Nothing to do here.
+    if (btn->state == BTN_STATE_IDLE) {
+        return;
+    }
+
+    // Reset animation state.
+    if (btn->state == BTN_STATE_PRESSED && btn->frame != 0) {
+        btn->frame = 0;
+    }
+
+    // Continue the animation.
+    if (btn->state == BTN_STATE_HOLD || btn->state == BTN_STATE_PRESSED ) {
+        if(btn->frame < btn->n_frames - 1) {
+            btn->frame++;
+        }
+    }
+
+    // Finish the animation and return to idle.
+    if (btn->state == BTN_STATE_RELEASED) {
+        if (btn->frame > 0 && btn->frame < btn->n_frames - 1) {
+            btn->frame++;
+        } else {
+            btn->frame = 0;
+            btn->state = BTN_STATE_IDLE;
+        }
+    }
+    for (size_t i = 0; i < btn->n_obj; ++i) {
+        AnimationEntry anim_frame = btn->animations[i][btn->frame];
+        int x = btn->sprites[i].x + anim_frame.x_offset;
+        int y = btn->sprites[i].y + anim_frame.y_offset;
+        int base_tile = btn->sprites[i].base_tile + anim_frame.tile_offset;
+
+        // Clear the previous x/y coordinate and base tiles.
+        btn->sprites[i].obj_attr_0 &= ~0xFF;
+        btn->sprites[i].obj_attr_1 &= ~0x1FF;
+        btn->sprites[i].obj_attr_2 &= ~0x3FF;
+
+        // Update x/y/tile and hidden state from the animations.
+        btn->sprites[i].obj_attr_0 |= OBJ_Y_COORD(y);
+        btn->sprites[i].obj_attr_1 |= OBJ_X_COORD(x);
+        btn->sprites[i].obj_attr_2 |= base_tile;
+        if (anim_frame.hidden) {
+            btn->sprites[i].obj_attr_0 |= OBJ_HIDDEN;
+        } else {
+            btn->sprites[i].obj_attr_0 &= ~OBJ_HIDDEN;
+        }
+
+        // Update OBJ attributes.
+        OBJ_ATTR_0(btn->sprites[i].id) = btn->sprites[i].obj_attr_0;
+        OBJ_ATTR_1(btn->sprites[i].id) = btn->sprites[i].obj_attr_1;
+        OBJ_ATTR_2(btn->sprites[i].id) = btn->sprites[i].obj_attr_2;
+    }
+}
+
+ButtonSprite buttons[] = {
+    // DOWN.
+    {
+        .frame = 0,
+        .n_obj = 3,
+        .n_frames = 8,
+        .state = BTN_STATE_RELEASED,
+        .animations = &btn_animation,
+        .sprites = &(ObjState[]){
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 16,
+                .y = SCREEN_HEIGHT / 2 + 29,
+                .data = &gba_btn_updown_data,
+                .n_tiles = 4,
+                .frames = 1,
+                .obj_attr_0 = 0,
+                .obj_attr_1 = OBJ_V_FLIP | OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 16,
+                .y = SCREEN_HEIGHT / 2 + 29 + 11,
+                .data = &gba_btn_down_shadow_data,
+                .n_tiles = 2,
+                .frames = 1,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_SMALL,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 16 - 8,
+                .y = SCREEN_HEIGHT / 2 + 29 + 17,
+                .data = &gba_btn_fx_downup,
+                .n_tiles = 4,
+                .frames = 4,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+        },
+    },
+    // UP.
+    {
+        .frame = 0,
+        .n_obj = 3,
+        .n_frames = 8,
+        .state = BTN_STATE_RELEASED,
+        .animations = &btn_animation,
+        .sprites = &(ObjState[]){
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 16,
+                .y = SCREEN_HEIGHT / 2 + 32 - 18,
+                .data = &gba_btn_updown_data,
+                .n_tiles = 4,
+                .frames = 1,
+                .obj_attr_0 = 0,
+                .obj_attr_1 = OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 16,
+                .y = SCREEN_HEIGHT / 2 + 32 - 18 + 7,
+                .data = &gba_btn_up_shadow_data,
+                .n_tiles = 2,
+                .frames = 1,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_SMALL,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 16 - 8,
+                .y = SCREEN_HEIGHT / 2 + 32 - 18 - 7,
+                .data = &gba_btn_fx_downup,
+                .n_tiles = 4,
+                .frames = 4,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_V_FLIP | OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+        },
+    },
+    // LEFT
+    {
+        .frame = 0,
+        .n_obj = 3,
+        .n_frames = 8,
+        .state = BTN_STATE_RELEASED,
+        .animations = &btn_animation,
+        .sprites = &(ObjState[]){
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 16 - 10,
+                .y = SCREEN_HEIGHT / 2 + 32 - 10,
+                .data = &gba_btn_leftright_data,
+                .n_tiles = 4,
+                .frames = 1,
+                .obj_attr_0 = 0,
+                .obj_attr_1 = OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 16 - 10,
+                .y = SCREEN_HEIGHT / 2 + 32 - 10 + 6,
+                .data = &gba_btn_leftright_shadow_data,
+                .n_tiles = 2,
+                .frames = 1,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_SMALL,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 16 - 10 - 6,
+                .y = SCREEN_HEIGHT / 2 + 32 - 10 - 8,
+                .data = &gba_btn_fx_leftright,
+                .n_tiles = 4,
+                .frames = 4,
+                .obj_attr_0 = OBJ_SHAPE_TALL,
+                .obj_attr_1 = OBJ_H_FLIP | OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+        },
+    },
+    // RIGHT.
+    {
+        .frame = 0,
+        .n_obj = 3,
+        .n_frames = 8,
+        .state = BTN_STATE_RELEASED,
+        .animations = &btn_animation,
+        .sprites = &(ObjState[]){
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 16 + 11,
+                .y = SCREEN_HEIGHT / 2 + 32 - 10,
+                .data = &gba_btn_leftright_data,
+                .n_tiles = 4,
+                .frames = 1,
+                .obj_attr_0 = 0,
+                .obj_attr_1 = OBJ_H_FLIP | OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 16 + 11,
+                .y = SCREEN_HEIGHT / 2 + 32 - 10 + 6,
+                .data = &gba_btn_leftright_shadow_data,
+                .n_tiles = 2,
+                .frames = 1,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_H_FLIP | OBJ_SIZE_SMALL,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 16 + 11 + 14,
+                .y = SCREEN_HEIGHT / 2 + 32 - 10 - 8,
+                .data = &gba_btn_fx_leftright,
+                .n_tiles = 4,
+                .frames = 4,
+                .obj_attr_0 = OBJ_SHAPE_TALL,
+                .obj_attr_1 = OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+        },
+    },
+    // L.
+    {
+        .frame = 0,
+        .n_obj = 3,
+        .n_frames = 8,
+        .state = BTN_STATE_RELEASED,
+        .animations = &btn_animation,
+        .sprites = &(ObjState[]){
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 28,
+                .y = SCREEN_HEIGHT / 2 - 32 - 20,
+                .data = &gba_btn_l_data,
+                .n_tiles = 2,
+                .frames = 1,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_SMALL,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 28,
+                .y = SCREEN_HEIGHT / 2 - 32 - 20 + 2,
+                .data = &gba_btn_lr_shadow_data,
+                .n_tiles = 2,
+                .frames = 1,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_SMALL,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 64 - 28 - 12,
+                .y = SCREEN_HEIGHT / 2 - 32 - 20 - 12,
+                .data = &gba_btn_fx_lr,
+                .n_tiles = 4,
+                .frames = 4,
+                .obj_attr_0 = OBJ_SHAPE_SQUARE,
+                .obj_attr_1 = OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+        },
+    },
+    // R.
+    {
+        .frame = 0,
+        .n_obj = 3,
+        .n_frames = 8,
+        .state = BTN_STATE_RELEASED,
+        .animations = &btn_animation,
+        .sprites = &(ObjState[]){
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 + 32 + 20 + 24,
+                .y = SCREEN_HEIGHT / 2 - 32 - 20,
+                .data = &gba_btn_r_data,
+                .n_tiles = 2,
+                .frames = 1,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_SMALL,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 + 32 + 20 + 24,
+                .y = SCREEN_HEIGHT / 2 - 32 - 20 + 2,
+                .data = &gba_btn_lr_shadow_data,
+                .n_tiles = 2,
+                .frames = 1,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_SMALL,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 + 32 + 20 + 12 + 24,
+                .y = SCREEN_HEIGHT / 2 - 32 - 20 - 12,
+                .data = &gba_btn_fx_lr,
+                .n_tiles = 4,
+                .frames = 4,
+                .obj_attr_0 = OBJ_SHAPE_SQUARE,
+                .obj_attr_1 = OBJ_H_FLIP | OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+        },
+    },
+    // A.
+    {
+        .frame = 0,
+        .n_obj = 3,
+        .n_frames = 8,
+        .state = BTN_STATE_RELEASED,
+        .animations = &btn_animation_ab,
+        .sprites = &(ObjState[]){
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 + 32 + 20 + 20,
+                .y = SCREEN_HEIGHT / 2 + 32 - 16,
+                .data = &gba_btn_a_data,
+                .n_tiles = 4,
+                .frames = 1,
+                .obj_attr_0 = OBJ_SHAPE_SQUARE,
+                .obj_attr_1 = OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 + 32 + 20 + 20,
+                .y = SCREEN_HEIGHT / 2 + 32 - 16 + 8,
+                .data = &gba_btn_ab_shadow_data,
+                .n_tiles = 2,
+                .frames = 1,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_SMALL,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 + 32 + 19 - 7 + 20,
+                .y = SCREEN_HEIGHT / 2 + 32 - 23,
+                .data = &gba_btn_fx_ab,
+                .n_tiles = 16,
+                .frames = 3,
+                .obj_attr_0 = OBJ_SHAPE_SQUARE,
+                .obj_attr_1 = OBJ_SIZE_BIG,
+                .obj_attr_2 = 0
+            },
+        },
+    },
+    // B.
+    {
+        .frame = 0,
+        .n_obj = 3,
+        .n_frames = 8,
+        .state = BTN_STATE_RELEASED,
+        .animations = &btn_animation_ab,
+        .sprites = &(ObjState[]){
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 + 32 + 20,
+                .y = SCREEN_HEIGHT / 2 + 32,
+                .data = &gba_btn_b_data,
+                .n_tiles = 4,
+                .frames = 1,
+                .obj_attr_0 = OBJ_SHAPE_SQUARE,
+                .obj_attr_1 = OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 + 32 + 20,
+                .y = SCREEN_HEIGHT / 2 + 32 + 8,
+                .data = &gba_btn_ab_shadow_data,
+                .n_tiles = 2,
+                .frames = 1,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_SMALL,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 + 32 - 8 + 20,
+                .y = SCREEN_HEIGHT / 2 + 33 + 8 - 16,
+                .data = &gba_btn_fx_ab,
+                .n_tiles = 16,
+                .frames = 3,
+                .obj_attr_0 = OBJ_SHAPE_SQUARE,
+                .obj_attr_1 = OBJ_SIZE_BIG,
+                .obj_attr_2 = 0
+            },
+        },
+    },
+    // START.
+    {
+        .frame = 0,
+        .n_obj = 3,
+        .n_frames = 8,
+        .state = BTN_STATE_RELEASED,
+        .animations = &btn_animation_startselect,
+        .sprites = &(ObjState[]){
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 10 + 26 - 14,
+                .y = SCREEN_HEIGHT / 2 + 40 + 10,
+                .data = &gba_btn_startselect_data,
+                .n_tiles = 2,
+                .frames = 2,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_SMALL,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 18 + 26 - 14,
+                .y = SCREEN_HEIGHT / 2 + 46 + 10,
+                .data = &gba_btn_start_text,
+                .n_tiles = 4,
+                .frames = 1,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 19 + 26 - 14,
+                .y = SCREEN_HEIGHT / 2 + 37 + 10,
+                .data = &gba_btn_fx_startselect,
+                .n_tiles = 4,
+                .frames = 4,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+        },
+    },
+    // SELECT.
+    {
+        .frame = 0,
+        .n_obj = 3,
+        .n_frames = 8,
+        .state = BTN_STATE_RELEASED,
+        .animations = &btn_animation_startselect,
+        .sprites = &(ObjState[]){
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 10 - 14,
+                .y = SCREEN_HEIGHT / 2 + 40 + 10,
+                .data = &gba_btn_startselect_data,
+                .n_tiles = 2,
+                .frames = 2,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_SMALL,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 18 - 14,
+                .y = SCREEN_HEIGHT / 2 + 46 + 10,
+                .data = &gba_btn_select_text,
+                .n_tiles = 4,
+                .frames = 1,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+            {
+                .id = 0,
+                .x = SCREEN_WIDTH / 2 - 19 - 14,
+                .y = SCREEN_HEIGHT / 2 + 37 + 10,
+                .data = &gba_btn_fx_startselect,
+                .n_tiles = 4,
+                .frames = 4,
+                .obj_attr_0 = OBJ_SHAPE_WIDE,
+                .obj_attr_1 = OBJ_SIZE_MID,
+                .obj_attr_2 = 0
+            },
+        },
+    },
+};
+
+static inline void
+init_button_sprites(void) {
+    for (size_t i = 0; i < sizeof(buttons) / sizeof(ButtonSprite); ++i) {
+        init_button_sprite(&buttons[i]);
+    }
+}
+
+static inline void
+update_button_sprites(void) {
+    if (key_pressed(KEY_DOWN)) {
+        buttons[0].state = BTN_STATE_PRESSED;
+    } else if (key_hold(KEY_DOWN)) {
+        buttons[0].state = BTN_STATE_HOLD;
+    } else {
+        buttons[0].state = BTN_STATE_RELEASED;
+    }
+    if (key_pressed(KEY_UP)) {
+        buttons[1].state = BTN_STATE_PRESSED;
+    } else if (key_hold(KEY_UP)) {
+        buttons[1].state = BTN_STATE_HOLD;
+    } else {
+        buttons[1].state = BTN_STATE_RELEASED;
+    }
+    if (key_pressed(KEY_LEFT)) {
+        buttons[2].state = BTN_STATE_PRESSED;
+    } else if (key_hold(KEY_LEFT)) {
+        buttons[2].state = BTN_STATE_HOLD;
+    } else {
+        buttons[2].state = BTN_STATE_RELEASED;
+    }
+    if (key_pressed(KEY_RIGHT)) {
+        buttons[3].state = BTN_STATE_PRESSED;
+    } else if (key_hold(KEY_RIGHT)) {
+        buttons[3].state = BTN_STATE_HOLD;
+    } else {
+        buttons[3].state = BTN_STATE_RELEASED;
+    }
+    if (key_pressed(KEY_L)) {
+        buttons[4].state = BTN_STATE_PRESSED;
+    } else if (key_hold(KEY_L)) {
+        buttons[4].state = BTN_STATE_HOLD;
+    } else {
+        buttons[4].state = BTN_STATE_RELEASED;
+    }
+    if (key_pressed(KEY_R)) {
+        buttons[5].state = BTN_STATE_PRESSED;
+    } else if (key_hold(KEY_R)) {
+        buttons[5].state = BTN_STATE_HOLD;
+    } else {
+        buttons[5].state = BTN_STATE_RELEASED;
+    }
+    if (key_pressed(KEY_A)) {
+        buttons[6].state = BTN_STATE_PRESSED;
+    } else if (key_hold(KEY_A)) {
+        buttons[6].state = BTN_STATE_HOLD;
+    } else {
+        buttons[6].state = BTN_STATE_RELEASED;
+    }
+    if (key_pressed(KEY_B)) {
+        buttons[7].state = BTN_STATE_PRESSED;
+    } else if (key_hold(KEY_B)) {
+        buttons[7].state = BTN_STATE_HOLD;
+    } else {
+        buttons[7].state = BTN_STATE_RELEASED;
+    }
+    if (key_pressed(KEY_START)) {
+        buttons[8].state = BTN_STATE_PRESSED;
+    } else if (key_hold(KEY_START)) {
+        buttons[8].state = BTN_STATE_HOLD;
+    } else {
+        buttons[8].state = BTN_STATE_RELEASED;
+    }
+    if (key_pressed(KEY_SELECT)) {
+        buttons[9].state = BTN_STATE_PRESSED;
+    } else if (key_hold(KEY_SELECT)) {
+        buttons[9].state = BTN_STATE_HOLD;
+    } else {
+        buttons[9].state = BTN_STATE_RELEASED;
+    }
+
+    for (size_t i = 0; i < sizeof(buttons) / sizeof(ButtonSprite); ++i) {
+        button_tick(&buttons[i]);
+    }
+}
diff --git a/src/main.c b/src/main.c
index 3002f7e..b8f2334 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,677 +1,17 @@
 #include <string.h>
 
-#include "shorthand.h"
-#include "bd-font.c"
+#include "common.h"
 #include "gba-buttons.c"
 #include "background-tiles.c"
-
-//
-// Memory sections.
-//
-
-// Defines for the different memory sections in the GBA.
-#define MEM_SROM  0x00000000
-#define MEM_EW    0x02000000
-#define MEM_IW    0x03000000
-#define MEM_IO    0x04000000
-#define MEM_PAL   0x05000000
-#define MEM_VRAM  0x06000000
-#define MEM_OAM   0x07000000
-#define MEM_PAK   0x08000000
-#define MEM_CART  0x0E000000
-
-//
-// Display modes.
-//
-
-// Display registers.
-#define DISP_CTRL   *((vu32*)(MEM_IO + 0x0000))
-#define DISP_STATUS *((vu16*)(MEM_IO + 0x0004))
-#define DISP_VCOUNT *((vu16*)(MEM_IO + 0x0006))
-
-// The first three bits in the DISP_CTRL are used to control the video mode.
-#define DISP_MODE_0     0x0000
-#define DISP_MODE_1     0x0001
-#define DISP_MODE_2     0x0002
-#define DISP_MODE_3     0x0003
-#define DISP_MODE_4     0x0004
-#define DISP_MODE_5     0x0005
-#define DISP_GB         (1 << 3)
-#define DISP_PAGE       (1 << 4)
-#define DISP_OAM_HBLANK (1 << 5)
-#define DISP_OBJ_1D     (1 << 6)
-#define DISP_BLANK      (1 << 7)
-#define DISP_BG_0       (1 << 8)
-#define DISP_BG_1       (1 << 9)
-#define DISP_BG_2       (1 << 10)
-#define DISP_BG_3       (1 << 11)
-#define DISP_OBJ        (1 << 12)
-#define DISP_ENABLE_SPRITES DISP_OBJ | DISP_OBJ_1D
-
-// Registers to control of BG layers.
-#define BG_CTRL_0 *((vu16*)(0x04000008 + 0x0002 * 0))
-#define BG_CTRL_1 *((vu16*)(0x04000008 + 0x0002 * 1))
-#define BG_CTRL_2 *((vu16*)(0x04000008 + 0x0002 * 2))
-#define BG_CTRL_3 *((vu16*)(0x04000008 + 0x0002 * 3))
-
-// Bits to control the background.
-#define BG_PRIORITY_0     0x0
-#define BG_PRIORITY_1     0x1
-#define BG_PRIORITY_2     0x2
-#define BG_PRIORITY_3     0x3
-#define BG_CHARBLOCK(N)   ((N) << 2)
-#define BG_MOSAIC         (1 << 6)
-#define BG_HIGH_COLOR     (1 << 7)
-#define BG_SCREENBLOCK(N) ((N) << 8)
-#define BG_AFFINE         (1 << 0xD)
-#define BG_SIZE(N)        ((N) << 0xE)
-
-// BG registers for horizontal displacement.
-#define BG_H_SCROLL_0 *((vu16*)(0x04000010 + 0x0004 * 0))
-#define BG_H_SCROLL_1 *((vu16*)(0x04000010 + 0x0004 * 1))
-#define BG_H_SCROLL_2 *((vu16*)(0x04000010 + 0x0004 * 2))
-#define BG_H_SCROLL_3 *((vu16*)(0x04000010 + 0x0004 * 3))
-
-// BG registers for vertical displacement.
-#define BG_V_SCROLL_0 *((vu16*)(0x04000012 + 0x0004 * 0))
-#define BG_V_SCROLL_1 *((vu16*)(0x04000012 + 0x0004 * 1))
-#define BG_V_SCROLL_2 *((vu16*)(0x04000012 + 0x0004 * 2))
-#define BG_V_SCROLL_3 *((vu16*)(0x04000012 + 0x0004 * 3))
-
-// Screen settings.
-#define SCREEN_WIDTH 240
-#define SCREEN_HEIGHT 160
-
-// The GBA in mode 3 expects rbg15 colors in the VRAM, where each component
-// (RGB) have a 0--31 range. For example, pure red would be rgb15(31, 0, 0).
-typedef u16 Color;
-
-//
-// Tile memory access.
-//
-
-// NOTE: Only defining 4bpp tiles for now.
-typedef struct Tile {
-    u32 data[8];
-} Tile;
-
-typedef Tile TileBlock[512];
-#define TILE_MEM ((TileBlock*) MEM_VRAM)
-
-typedef u16 ScreenBlock[1024];
-#define SCREENBLOCK_MEM ((ScreenBlock*)MEM_VRAM)
-
-// We can treat the screen as a HxW matrix. With the following macro we can
-// write a pixel to the screen at the (x, y) position using:
-//
-//     FRAMEBUFFER[y][x] = color;
-//
-typedef Color Scanline[SCREEN_WIDTH];
-#define FRAMEBUFFER        ((Scanline*)MEM_VRAM)
-#define SCREEN_BUFFER      ((u16*) MEM_VRAM)
-#define PAL_BUFFER_BG      ((u16*) MEM_PAL)
-#define PAL_BUFFER_SPRITES ((u16*) 0x05000200)
-
-//
-// Colors.
-//
-
-static inline Color
-rgb15(u32 red, u32 green, u32 blue ) {
-    return (blue << 10) | (green << 5) | red;
-}
-
-#define COLOR_RED   rgb15(31, 0, 12)
-#define COLOR_BLUE  rgb15(2, 15, 30)
-#define COLOR_CYAN  rgb15(0, 30, 30)
-#define COLOR_GREY  rgb15(4, 4, 4)
-#define COLOR_BLACK rgb15(0, 0, 0)
-#define COLOR_WHITE rgb15(28, 28, 28)
-
-//
-// Sprites.
-//
-
-// Using macros instead of aligned structs for setting up OBJ attributes and
-// affine parameters.
-// TODO: Benchmark if this would be slower or the same that TONC's
-// implementation.
-#define OBJ_ATTR_0(N)    *((vu16*)(MEM_OAM + 0 + 8 * (N)))
-#define OBJ_ATTR_1(N)    *((vu16*)(MEM_OAM + 2 + 8 * (N)))
-#define OBJ_ATTR_2(N)    *((vu16*)(MEM_OAM + 4 + 8 * (N)))
-#define OBJ_AFFINE_PA(N) *((vs16*)(MEM_OAM + 6 + 8 * 0 + 8 * 4 * (N)))
-#define OBJ_AFFINE_PB(N) *((vs16*)(MEM_OAM + 6 + 8 * 1 + 8 * 4 * (N)))
-#define OBJ_AFFINE_PC(N) *((vs16*)(MEM_OAM + 6 + 8 * 2 + 8 * 4 * (N)))
-#define OBJ_AFFINE_PD(N) *((vs16*)(MEM_OAM + 6 + 8 * 3 + 8 * 4 * (N)))
-
-// OBJ_ATTR_0 parameters
-#define OBJ_Y_COORD(N)   ((N) & 0xFF)
-#define OBJ_NORMAL       (0x00 << 0x8)
-#define OBJ_AFFINE       (0x01 << 0x8)
-#define OBJ_HIDDEN       (0x02 << 0x8)
-#define OBJ_AFFINE_2X    (0x03 << 0x8)
-#define OBJ_ALPHA_BLEND  (0x01 << 0xA)
-#define OBJ_WINDOW       (0x02 << 0xA)
-#define OBJ_SHAPE_SQUARE (0x00 << 0xE)
-#define OBJ_SHAPE_WIDE   (0x01 << 0xE)
-#define OBJ_SHAPE_TALL   (0x02 << 0xE)
-
-// OBJ_ATTR_1 parameters
-#define OBJ_X_COORD(N)    ((N) & 0x1FF)
-#define OBJ_AFFINE_IDX(N) ((N) << 0x9)
-#define OBJ_H_FLIP        (0x01 << 0xC)
-#define OBJ_V_FLIP        (0x01 << 0xD)
-#define OBJ_SIZE_SMALL    (0x00 << 0xE)
-#define OBJ_SIZE_MID      (0x01 << 0xE)
-#define OBJ_SIZE_BIG      (0x02 << 0xE)
-#define OBJ_SIZE_HUGE     (0x03 << 0xE)
-
-// OBJ_ATTR_2 parameters
-#define OBJ_TILE_INDEX(N) ((N) & 0x3FF)
-#define OBJ_PRIORITY(N)   ((N) << 0xA)
-#define OBJ_PAL_BANK(N)   ((N) << 0xC)
-
-// Using bd-font, an 8x8 bitmap font.
-static void
-put_char(int x, int y, Color clr, u8 chr) {
-    for (size_t i = 0; i < 8; ++i) {
-        for (size_t j = 0; j < 8; ++j) {
-            if ((font[chr][i] >> (7 - j)) & 0x1) {
-                FRAMEBUFFER[y + i][x + j] = clr;
-            }
-        }
-    }
-}
-
-static void
-put_text(int x, int y, Color clr, char *msg) {
-    int count = 0;
-    while (*msg) {
-        put_char(x + count, y, clr, *msg++);
-        count += 8;
-    }
-}
-
-// Draws a line with the given color between (x0,y0) and (x1,y1) using the
-// Bresenham's line drawing algorithm using exclusively integer arithmetic.
-static void
-draw_line(int x0, int y0, int x1, int y1, Color clr) {
-    // Pointer to the initial position of the screen buffer where we will start
-    // writing our data.
-    vu16 *destination = (u16*)(SCREEN_BUFFER + y0 * SCREEN_WIDTH + x0);
-
-    // Adjust the step direction and calculate deltas.
-    int x_step;
-    int y_step;
-    int dx;
-    int dy;
-    if (x0 > x1) {
-        x_step = -1;
-        dx = x0 - x1;
-    } else {
-        x_step = 1;
-        dx = x1 - x0;
-    }
-    if (y0 > y1) {
-        y_step = -SCREEN_WIDTH;
-        dy = y0 - y1;
-    } else {
-        y_step = +SCREEN_WIDTH;
-        dy = y1 - y0;
-    }
-
-    if(dy == 0) {
-        // Horizontal line.
-        for(int i = 0; i <= dx; i++) {
-            destination[i * x_step] = clr;
-        }
-    } else if(dx == 0) {
-        // Vertical line.
-        for(int i = 0; i <= dy; i++) {
-            destination[i * y_step] = clr;
-        }
-    } else if (dx >= dy){
-        // Positive slope.
-        int diff = 2 * dy - dx;
-        for (int i = 0; i <= dx; ++i) {
-            *destination = clr;
-            if (diff >= 0) {
-                destination += y_step;
-                diff -= 2 * dx;
-            }
-            destination += x_step;
-            diff += 2 * dy;
-        }
-    } else {
-        // Negative slope.
-        int diff = 2 * dx - dy;
-        for (int i = 0; i <= dy; ++i) {
-            *destination = clr;
-            if (diff >= 0) {
-                destination += x_step;
-                diff -= 2 * dy;
-            }
-            destination += y_step;
-            diff += 2 * dx;
-        }
-    }
-}
-
-static inline void
-draw_rect(int x0, int y0, int x1, int y1, Color clr) {
-    if (x0 > x1) {
-        int tmp = x0;
-        x0 = x1;
-        x1 = tmp;
-    }
-    if (y0 > y1) {
-        int tmp = y0;
-        y0 = y1;
-        y1 = tmp;
-    }
-    int dx = x1 - x0;
-    int dy = y1 - y0;
-    for (int i = 0; i <= dx; ++i) {
-        int x = x0 + i;
-        FRAMEBUFFER[y0][x] = clr;
-        FRAMEBUFFER[y1][x] = clr;
-    }
-    for (int j = 0; j <= dy; ++j) {
-        int y = y0 + j;
-        FRAMEBUFFER[y][x0] = clr;
-        FRAMEBUFFER[y][x1] = clr;
-    }
-}
-
-static inline void
-draw_fill_rect(int x0, int y0, int x1, int y1, Color clr) {
-    if (x0 > x1) {
-        int tmp = x0;
-        x0 = x1;
-        x1 = tmp;
-    }
-    if (y0 > y1) {
-        int tmp = y0;
-        y0 = y1;
-        y1 = tmp;
-    }
-    int dx = x1 - x0;
-    int dy = y1 - y0;
-    for (int i = 0; i <= dx; ++i) {
-        for (int j = 0; j <= dy; ++j) {
-            int x = x0 + i;
-            int y = y0 + j;
-            FRAMEBUFFER[y][x] = clr;
-        }
-    }
-}
-
-static inline void
-wait_vsync(void) {
-    while(DISP_VCOUNT >= 160);
-    while(DISP_VCOUNT < 160);
-}
+#include "sprites.h"
 
 //
 // Main functions.
 //
 
-// In Mode4 the buffer is of 8 bytes per pixel instead of 16. We can't write the
-// color directly, instead the color is stored in the palette memory at
-// `MEM_PAL`. Note that in this mode MEM_PAL[0] is the background color. This
-// plotter takes an index to a color stored in MEM_PAL[col_index]. Because the
-// GBA needs to meet memory alignment requirements, we can't write a u8 into
-// memory, instead we need to read a u16 word, mask and or the corresponding
-// bits and wave the updated u16.
-static void
-put_pixel_m4(int x, int y, u8 col_index, vu16 *buffer) {
-    int buffer_index = (y * SCREEN_WIDTH + x) / 2;
-    vu16 *destination = &buffer[buffer_index];
-    // Odd pixels will go to the top 8 bits of the destination. Even pixels to
-    // the lower 8 bits.
-    int odd = x & 0x1;
-    if(odd) {
-        *destination= (*destination & 0xFF) | (col_index << 8);
-    } else {
-        *destination= (*destination & ~0xFF) |  col_index;
-    }
-}
-
-static void
-draw_fill_rect_m4(int x0, int y0, int x1, int y1, u8 col_index, vu16 *buffer) {
-    int ix, iy;
-    for(iy = y0; iy < y1; iy++) {
-        for(ix = x0; ix < x1; ix++) {
-            put_pixel_m4(ix, iy, col_index, buffer);
-        }
-    }
-}
-
-static inline void
-flip_page(void) {
-    DISP_CTRL ^= DISP_PAGE;
-}
-
-#define SCREEN_PAGE_1 ((vu16*) MEM_VRAM)
-#define SCREEN_PAGE_2 ((vu16*) (MEM_VRAM + 0xa000))
-
-//
-// Profiling.
-//
-
-#define TIMER_DATA_0  *((vu16*) (0x04000100 + 0x04 * 0))
-#define TIMER_DATA_1  *((vu16*) (0x04000100 + 0x04 * 1))
-#define TIMER_DATA_2  *((vu16*) (0x04000100 + 0x04 * 2))
-#define TIMER_DATA_3  *((vu16*) (0x04000100 + 0x04 * 3))
-#define TIMER_CTRL_0  *((vu16*) (0x04000102 + 0x04 * 0))
-#define TIMER_CTRL_1  *((vu16*) (0x04000102 + 0x04 * 1))
-#define TIMER_CTRL_2  *((vu16*) (0x04000102 + 0x04 * 2))
-#define TIMER_CTRL_3  *((vu16*) (0x04000102 + 0x04 * 3))
-
-// Timer control bits.
-#define TIMER_CTRL_FREQ_0   0
-#define TIMER_CTRL_FREQ_1   1
-#define TIMER_CTRL_FREQ_2   2
-#define TIMER_CTRL_FREQ_3   3
-#define TIMER_CTRL_CASCADE (1 << 2)
-#define TIMER_CTRL_IRQ     (1 << 6)
-#define TIMER_CTRL_ENABLE  (1 << 7)
-
-// We use timers 2 and 3 to count the number of cycles since the profile_start
-// functions is called. Don't use if the code we are trying to profile make use
-// of these timers.
-static inline
-void profile_start(void) {
-    TIMER_DATA_2 = 0;
-    TIMER_DATA_3 = 0;
-    TIMER_CTRL_2 = 0;
-    TIMER_CTRL_3 = 0;
-    TIMER_CTRL_3 = TIMER_CTRL_ENABLE | TIMER_CTRL_CASCADE;
-    TIMER_CTRL_2 = TIMER_CTRL_ENABLE;
-}
-
-static inline
-u32 profile_stop(void) {
-   TIMER_CTRL_2 = 0;
-   return (TIMER_DATA_3 << 16) | TIMER_DATA_2;
-}
-
-//
-// Input handling.
-//
-
-// Memory address for key input register
-#define KEY_INPUTS *((vu16*) 0x04000130)
-
-// Alias for key pressing bits.
-#define KEY_A      (1 << 0)
-#define KEY_B      (1 << 1)
-#define KEY_SELECT (1 << 2)
-#define KEY_START  (1 << 3)
-#define KEY_RIGHT  (1 << 4)
-#define KEY_LEFT   (1 << 5)
-#define KEY_UP     (1 << 6)
-#define KEY_DOWN   (1 << 7)
-#define KEY_R      (1 << 8)
-#define KEY_L      (1 << 9)
-
-#define KEY_MASK 0x03FF
-
-// Saving the previous and current key states as globals for now.
-static u16 key_curr = 0;
-static u16 key_prev = 0;
-
-static inline void
-poll_keys(void) {
-    key_prev = key_curr;
-    key_curr = ~KEY_INPUTS & KEY_MASK;
-}
-
-// Returns true if the given key has been pressed at time of calling and was not
-// pressed since the previous call. For example, if a key is being held, this
-// function will return `true` only on the frame where the key initially
-// activated.
-static inline u32
-key_pressed(u32 key) {
-    return (key_curr & key) & ~(key_prev & key);
-}
-
-// Check if the given key is pressed and has been since at least one frame.
-static inline u32
-key_hold(u32 key) {
-    return (key_curr & key) & key_prev & key;
-}
-
-// Check if the given key/button is currently pressed.
-#define KEY_PRESSED(key) (~(KEY_INPUTS) & key)
-
-void
-draw_logo(void) {
-    int side = 60;
-    int line = 35;
-    int height = side * 0.5;
-    int x = SCREEN_WIDTH / 2 - height / 2;
-    int y = SCREEN_HEIGHT / 2;
-
-    // Draw red triangle.
-    draw_line(x + height - 1, y - side / 2, x, y - 1, COLOR_RED);
-    draw_line(x + height - 1, y + side / 2, x, y + 1, COLOR_RED);
-    draw_line(x + height - 1, y - side / 2 + 1, x, y, COLOR_RED);
-    draw_line(x + height - 1, y + side / 2 - 1, x, y, COLOR_RED);
-
-    // Draw white triangle.
-    draw_line(x, y - side / 2, x, y + side / 2, COLOR_WHITE);
-    draw_line(x + 1, y - side / 2, x + height, y - 1, COLOR_WHITE);
-    draw_line(x + 1, y + side / 2, x + height, y + 1, COLOR_WHITE);
-
-    // Draw white line at triangle tip.
-    draw_line(x + height, y - side / 2, x + height, y + side / 2, COLOR_WHITE);
-    draw_line(x + height + 1, y - side / 2, x + height + 1, y + side / 2, COLOR_WHITE);
-
-    // Double triangle line.
-    draw_line(x - 1, y - side / 2, x - 1, y + side / 2, COLOR_WHITE);
-    draw_line(x + 1, y - side / 2 + 1, x + height, y, COLOR_WHITE);
-    draw_line(x + 1, y + side / 2 - 1, x + height, y, COLOR_WHITE);
-
-    // Draw white lines.
-    draw_line(x - line, y, x, y, COLOR_WHITE);
-    draw_line(x + height, y, x + height + line, y, COLOR_WHITE);
-    draw_line(x - line, y + 1, x, y + 1, COLOR_WHITE);
-    draw_line(x + height, y + 1, x + height + line, y + 1, COLOR_WHITE);
-}
-
-void
-copy_font_to_tile_memory(Tile *tile) {
-    // Hex to bits translation table.
-    const u32 conversion_u32[16] = {
-        0x00000000, 0x00001000, 0x00000100, 0x00001100,
-        0x00000010, 0x00001010, 0x00000110, 0x00001110,
-        0x00000001, 0x00001001, 0x00000101, 0x00001101,
-        0x00000011, 0x00001011, 0x00000111, 0x00001111,
-    };
-    for (size_t i = 0; i < 250; ++i) {
-        for (size_t j = 0; j < 8; ++j) {
-            u8 row = font[i][j];
-            u32 tile_idx = 0x00000000;
-            tile_idx = conversion_u32[row & 0xF] << 16;
-            tile_idx |= conversion_u32[(row >> 4) & 0xF];
-            (tile + i)->data[j] = tile_idx;
-        }
-    }
-}
-
-
-u32
-unpack_1bb(u8 hex) {
-    const u32 conversion_u32[16] = {
-        0x00000000, 0x00000001, 0x00000010, 0x00000011,
-        0x00000100, 0x00000101, 0x00000110, 0x00000111,
-        0x00001000, 0x00001001, 0x00001010, 0x00001011,
-        0x00001100, 0x00001101, 0x00001110, 0x00001111,
-    };
-    u8 low = hex & 0xF;
-    u8 high = (hex >> 4) & 0xF;
-    return (conversion_u32[high] << 16) | conversion_u32[low];
-}
-
-typedef struct Sprite {
-    // A unique sprite identifier.
-    size_t id;
-    // The number of tiles for a single sprite frame.
-    size_t n_tiles;
-    // The starting tile of this sprite.
-    size_t tile_start;
-    // The associated palette bank for this sprite.
-    size_t pal_bank;
-} Sprite;
-
-typedef struct ButtonSprite {
-    int id;
-    int x;
-    int y;
-    int frame;
-    BtnState state;
-} ButtonSprite;
-
-typedef struct MultiSprite {
-    ObjState *sprites;
-    AnimationEntry **animations;
-    size_t frame;
-    size_t n_obj;
-    size_t n_frames;
-    BtnState state;
-} MultiSprite;
-
-#define NUM_SPRITES 128
-
-Sprite sprites[NUM_SPRITES];
-
-// Keeping track of unique sprites and current sprite memory pointer using
-// global singletons.
-size_t sprite_counter = 0;
-size_t sprite_tile_counter = 0;
-u32 *sprite_memory = NULL;
-
-// Loads the sprite data into video memory and initialize the Sprite structure.
-size_t
-load_sprite_data(u32 *sprite_data, size_t n_tiles, size_t n_frames) {
-    memcpy(sprite_memory, sprite_data, 8 * n_tiles * n_frames * sizeof(u32));
-    sprite_memory += 8 * n_tiles * n_frames;
-    Sprite sprite = {
-        .id = sprite_counter,
-        .n_tiles = n_tiles,
-        .tile_start = sprite_tile_counter,
-    };
-    sprite_tile_counter += n_tiles * n_frames;
-    sprites[sprite_counter] = sprite;
-    return sprite_counter++;
-}
-
-size_t
-load_packed_sprite_data(u32 *sprite_data, size_t n_tiles, size_t n_frames) {
-    size_t counter = 0;
-    for (size_t i = 0; i < 8 * n_tiles * n_frames / 4; ++i) {
-        u32 hex = sprite_data[i];
-        sprite_memory[counter++] = unpack_1bb((hex >> 24) & 0xFF);
-        sprite_memory[counter++] = unpack_1bb((hex >> 16) & 0xFF);
-        sprite_memory[counter++] = unpack_1bb((hex >> 8) & 0xFF);
-        sprite_memory[counter++] = unpack_1bb((hex) & 0xFF);
-    }
-    sprite_memory += 8 * n_tiles * n_frames;
-    Sprite sprite = {
-        .id = sprite_counter,
-        .n_tiles = n_tiles,
-        .tile_start = sprite_tile_counter,
-    };
-    sprite_tile_counter += n_tiles * n_frames;
-    sprites[sprite_counter] = sprite;
-    return sprite_counter++;
-}
-
-void
-init_button_sprite(MultiSprite *btn) {
-    for (size_t i = 0; i < btn->n_obj; ++i) {
-        btn->sprites[i].id = load_packed_sprite_data(
-                btn->sprites[i].data,
-                btn->sprites[i].n_tiles,
-                btn->sprites[i].frames);
-        btn->sprites[i].base_tile = sprites[btn->sprites[i].id].tile_start;
-    }
-}
-
-void
-button_tick(MultiSprite *btn) {
-    // Nothing to do here.
-    if (btn->state == BTN_STATE_IDLE) {
-        return;
-    }
-
-    // Reset animation state.
-    if (btn->state == BTN_STATE_PRESSED && btn->frame != 0) {
-        btn->frame = 0;
-    }
-
-    // Continue the animation.
-    if (btn->state == BTN_STATE_HOLD || btn->state == BTN_STATE_PRESSED ) {
-        if(btn->frame < btn->n_frames - 1) {
-            btn->frame++;
-        }
-    }
-
-    // Finish the animation and return to idle.
-    if (btn->state == BTN_STATE_RELEASED) {
-        if (btn->frame > 0 && btn->frame < btn->n_frames - 1) {
-            btn->frame++;
-        } else {
-            btn->frame = 0;
-            btn->state = BTN_STATE_IDLE;
-        }
-    }
-    for (size_t i = 0; i < btn->n_obj; ++i) {
-        AnimationEntry anim_frame = btn->animations[i][btn->frame];
-        int x = btn->sprites[i].x + anim_frame.x_offset;
-        int y = btn->sprites[i].y + anim_frame.y_offset;
-        int base_tile = btn->sprites[i].base_tile + anim_frame.tile_offset;
-
-        // Clear the previous x/y coordinate and base tiles.
-        btn->sprites[i].obj_attr_0 &= ~0xFF;
-        btn->sprites[i].obj_attr_1 &= ~0x1FF;
-        btn->sprites[i].obj_attr_2 &= ~0x3FF;
-
-        // Update x/y/tile and hidden state from the animations.
-        btn->sprites[i].obj_attr_0 |= OBJ_Y_COORD(y);
-        btn->sprites[i].obj_attr_1 |= OBJ_X_COORD(x);
-        btn->sprites[i].obj_attr_2 |= base_tile;
-        if (anim_frame.hidden) {
-            btn->sprites[i].obj_attr_0 |= OBJ_HIDDEN;
-        } else {
-            btn->sprites[i].obj_attr_0 &= ~OBJ_HIDDEN;
-        }
-
-        // Update OBJ attributes.
-        OBJ_ATTR_0(btn->sprites[i].id) = btn->sprites[i].obj_attr_0;
-        OBJ_ATTR_1(btn->sprites[i].id) = btn->sprites[i].obj_attr_1;
-        OBJ_ATTR_2(btn->sprites[i].id) = btn->sprites[i].obj_attr_2;
-    }
-}
+// TODO: Cleanup OBJ/OAM memory copying and access.
 
 int main(void) {
-
-    // Add colors to the sprite color palette. Tiles with color number 0 are
-    // treated as transparent.
-    for (size_t i = 0; i < 16; ++i) {
-        PAL_BUFFER_SPRITES[i] = COLOR_WHITE;
-    }
-
-    // Initialize all attributes by disabling rendering. If we don't do this,
-    // glitches may appear.
-    for (size_t i = 0; i < 128; ++i) {
-        OBJ_ATTR_0(i) = (1 << 9);
-    }
-
-    sprite_tile_counter = 0;
-    sprite_memory = &TILE_MEM[4][sprite_tile_counter];
-
     // Load background palette.
     memcpy(&PAL_BUFFER_BG[0], &bg_palette, 512);
     memcpy(&TILE_MEM[0][0], bg_data, 3168);
@@ -687,445 +27,10 @@ int main(void) {
     // sequential.
     DISP_CTRL = DISP_ENABLE_SPRITES | DISP_MODE_0 | DISP_BG_0;
 
-    // Initialize the A/B button sprites.
-    int buttons_x = SCREEN_WIDTH / 2;
-    int buttons_y = SCREEN_HEIGHT / 2;
-
-    MultiSprite buttons[] = {
-        // DOWN.
-        {
-            .frame = 0,
-            .n_obj = 3,
-            .n_frames = 8,
-            .state = BTN_STATE_RELEASED,
-            .animations = &btn_animation,
-            .sprites = &(ObjState[]){
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 16,
-                    .y = buttons_y + 29,
-                    .data = &gba_btn_updown_data,
-                    .n_tiles = 4,
-                    .frames = 1,
-                    .obj_attr_0 = 0,
-                    .obj_attr_1 = OBJ_V_FLIP | OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 16,
-                    .y = buttons_y + 29 + 11,
-                    .data = &gba_btn_down_shadow_data,
-                    .n_tiles = 2,
-                    .frames = 1,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_SMALL,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 16 - 8,
-                    .y = buttons_y + 29 + 17,
-                    .data = &gba_btn_fx_downup,
-                    .n_tiles = 4,
-                    .frames = 4,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-            },
-        },
-        // UP.
-        {
-            .frame = 0,
-            .n_obj = 3,
-            .n_frames = 8,
-            .state = BTN_STATE_RELEASED,
-            .animations = &btn_animation,
-            .sprites = &(ObjState[]){
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 16,
-                    .y = buttons_y + 32 - 18,
-                    .data = &gba_btn_updown_data,
-                    .n_tiles = 4,
-                    .frames = 1,
-                    .obj_attr_0 = 0,
-                    .obj_attr_1 = OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 16,
-                    .y = buttons_y + 32 - 18 + 7,
-                    .data = &gba_btn_up_shadow_data,
-                    .n_tiles = 2,
-                    .frames = 1,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_SMALL,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 16 - 8,
-                    .y = buttons_y + 32 - 18 - 7,
-                    .data = &gba_btn_fx_downup,
-                    .n_tiles = 4,
-                    .frames = 4,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_V_FLIP | OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-            },
-        },
-        // LEFT
-        {
-            .frame = 0,
-            .n_obj = 3,
-            .n_frames = 8,
-            .state = BTN_STATE_RELEASED,
-            .animations = &btn_animation,
-            .sprites = &(ObjState[]){
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 16 - 10,
-                    .y = buttons_y + 32 - 10,
-                    .data = &gba_btn_leftright_data,
-                    .n_tiles = 4,
-                    .frames = 1,
-                    .obj_attr_0 = 0,
-                    .obj_attr_1 = OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 16 - 10,
-                    .y = buttons_y + 32 - 10 + 6,
-                    .data = &gba_btn_leftright_shadow_data,
-                    .n_tiles = 2,
-                    .frames = 1,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_SMALL,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 16 - 10 - 6,
-                    .y = buttons_y + 32 - 10 - 8,
-                    .data = &gba_btn_fx_leftright,
-                    .n_tiles = 4,
-                    .frames = 4,
-                    .obj_attr_0 = OBJ_SHAPE_TALL,
-                    .obj_attr_1 = OBJ_H_FLIP | OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-            },
-        },
-        // RIGHT.
-        {
-            .frame = 0,
-            .n_obj = 3,
-            .n_frames = 8,
-            .state = BTN_STATE_RELEASED,
-            .animations = &btn_animation,
-            .sprites = &(ObjState[]){
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 16 + 11,
-                    .y = buttons_y + 32 - 10,
-                    .data = &gba_btn_leftright_data,
-                    .n_tiles = 4,
-                    .frames = 1,
-                    .obj_attr_0 = 0,
-                    .obj_attr_1 = OBJ_H_FLIP | OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 16 + 11,
-                    .y = buttons_y + 32 - 10 + 6,
-                    .data = &gba_btn_leftright_shadow_data,
-                    .n_tiles = 2,
-                    .frames = 1,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_H_FLIP | OBJ_SIZE_SMALL,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 16 + 11 + 14,
-                    .y = buttons_y + 32 - 10 - 8,
-                    .data = &gba_btn_fx_leftright,
-                    .n_tiles = 4,
-                    .frames = 4,
-                    .obj_attr_0 = OBJ_SHAPE_TALL,
-                    .obj_attr_1 = OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-            },
-        },
-        // L.
-        {
-            .frame = 0,
-            .n_obj = 3,
-            .n_frames = 8,
-            .state = BTN_STATE_RELEASED,
-            .animations = &btn_animation,
-            .sprites = &(ObjState[]){
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 28,
-                    .y = buttons_y - 32 - 20,
-                    .data = &gba_btn_l_data,
-                    .n_tiles = 2,
-                    .frames = 1,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_SMALL,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 28,
-                    .y = buttons_y - 32 - 20 + 2,
-                    .data = &gba_btn_lr_shadow_data,
-                    .n_tiles = 2,
-                    .frames = 1,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_SMALL,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x - 64 - 28 - 12,
-                    .y = buttons_y - 32 - 20 - 12,
-                    .data = &gba_btn_fx_lr,
-                    .n_tiles = 4,
-                    .frames = 4,
-                    .obj_attr_0 = OBJ_SHAPE_SQUARE,
-                    .obj_attr_1 = OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-            },
-        },
-        // R.
-        {
-            .frame = 0,
-            .n_obj = 3,
-            .n_frames = 8,
-            .state = BTN_STATE_RELEASED,
-            .animations = &btn_animation,
-            .sprites = &(ObjState[]){
-                {
-                    .id = 0,
-                    .x = buttons_x + 32 + 20 + 24,
-                    .y = buttons_y - 32 - 20,
-                    .data = &gba_btn_r_data,
-                    .n_tiles = 2,
-                    .frames = 1,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_SMALL,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x + 32 + 20 + 24,
-                    .y = buttons_y - 32 - 20 + 2,
-                    .data = &gba_btn_lr_shadow_data,
-                    .n_tiles = 2,
-                    .frames = 1,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_SMALL,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x + 32 + 20 + 12 + 24,
-                    .y = buttons_y - 32 - 20 - 12,
-                    .data = &gba_btn_fx_lr,
-                    .n_tiles = 4,
-                    .frames = 4,
-                    .obj_attr_0 = OBJ_SHAPE_SQUARE,
-                    .obj_attr_1 = OBJ_H_FLIP | OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-            },
-        },
-        // A.
-        {
-            .frame = 0,
-            .n_obj = 3,
-            .n_frames = 8,
-            .state = BTN_STATE_RELEASED,
-            .animations = &btn_animation_ab,
-            .sprites = &(ObjState[]){
-                {
-                    .id = 0,
-                    .x = buttons_x + 32 + 20 + 20,
-                    .y = buttons_y + 32 - 16,
-                    .data = &gba_btn_a_data,
-                    .n_tiles = 4,
-                    .frames = 1,
-                    .obj_attr_0 = OBJ_SHAPE_SQUARE,
-                    .obj_attr_1 = OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x + 32 + 20 + 20,
-                    .y = buttons_y + 32 - 16 + 8,
-                    .data = &gba_btn_ab_shadow_data,
-                    .n_tiles = 2,
-                    .frames = 1,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_SMALL,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x + 32 + 19 - 7 + 20,
-                    .y = buttons_y + 32 - 23,
-                    .data = &gba_btn_fx_ab,
-                    .n_tiles = 16,
-                    .frames = 3,
-                    .obj_attr_0 = OBJ_SHAPE_SQUARE,
-                    .obj_attr_1 = OBJ_SIZE_BIG,
-                    .obj_attr_2 = 0
-                },
-            },
-        },
-        // B.
-        {
-            .frame = 0,
-            .n_obj = 3,
-            .n_frames = 8,
-            .state = BTN_STATE_RELEASED,
-            .animations = &btn_animation_ab,
-            .sprites = &(ObjState[]){
-                {
-                    .id = 0,
-                    .x = buttons_x + 32 + 20,
-                    .y = buttons_y + 32,
-                    .data = &gba_btn_b_data,
-                    .n_tiles = 4,
-                    .frames = 1,
-                    .obj_attr_0 = OBJ_SHAPE_SQUARE,
-                    .obj_attr_1 = OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x + 32 + 20,
-                    .y = buttons_y + 32 + 8,
-                    .data = &gba_btn_ab_shadow_data,
-                    .n_tiles = 2,
-                    .frames = 1,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_SMALL,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x + 32 - 8 + 20,
-                    .y = buttons_y + 33 + 8 - 16,
-                    .data = &gba_btn_fx_ab,
-                    .n_tiles = 16,
-                    .frames = 3,
-                    .obj_attr_0 = OBJ_SHAPE_SQUARE,
-                    .obj_attr_1 = OBJ_SIZE_BIG,
-                    .obj_attr_2 = 0
-                },
-            },
-        },
-        // START.
-        {
-            .frame = 0,
-            .n_obj = 3,
-            .n_frames = 8,
-            .state = BTN_STATE_RELEASED,
-            .animations = &btn_animation_startselect,
-            .sprites = &(ObjState[]){
-                {
-                    .id = 0,
-                    .x = buttons_x - 10 - 14,
-                    .y = buttons_y + 40 + 10,
-                    .data = &gba_btn_startselect_data,
-                    .n_tiles = 2,
-                    .frames = 2,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_SMALL,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x - 18 - 14,
-                    .y = buttons_y + 46 + 10,
-                    .data = &gba_btn_start_text,
-                    .n_tiles = 4,
-                    .frames = 1,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x - 19 - 14,
-                    .y = buttons_y + 37 + 10,
-                    .data = &gba_btn_fx_startselect,
-                    .n_tiles = 4,
-                    .frames = 4,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-            },
-        },
-        // SELECT.
-        {
-            .frame = 0,
-            .n_obj = 3,
-            .n_frames = 8,
-            .state = BTN_STATE_RELEASED,
-            .animations = &btn_animation_startselect,
-            .sprites = &(ObjState[]){
-                {
-                    .id = 0,
-                    .x = buttons_x - 10 + 26 - 14,
-                    .y = buttons_y + 40 + 10,
-                    .data = &gba_btn_startselect_data,
-                    .n_tiles = 2,
-                    .frames = 2,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_SMALL,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x - 18 + 26 - 14,
-                    .y = buttons_y + 46 + 10,
-                    .data = &gba_btn_select_text,
-                    .n_tiles = 4,
-                    .frames = 1,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-                {
-                    .id = 0,
-                    .x = buttons_x - 19 + 26 - 14,
-                    .y = buttons_y + 37 + 10,
-                    .data = &gba_btn_fx_startselect,
-                    .n_tiles = 4,
-                    .frames = 4,
-                    .obj_attr_0 = OBJ_SHAPE_WIDE,
-                    .obj_attr_1 = OBJ_SIZE_MID,
-                    .obj_attr_2 = 0
-                },
-            },
-        },
-    };
-    for (size_t i = 0; i < sizeof(buttons) / sizeof(MultiSprite); ++i) {
-        init_button_sprite(&buttons[i]);
-    }
+    // Initialize sprite button overlay.
+    init_sprite_pal(0, COLOR_WHITE);
+    init_sprites(0);
+    init_button_sprites();
 
     int frame_counter = 0;
     int x = 0;
@@ -1134,77 +39,6 @@ int main(void) {
         wait_vsync();
         poll_keys();
 
-        if (key_pressed(KEY_DOWN)) {
-            buttons[0].state = BTN_STATE_PRESSED;
-        } else if (key_hold(KEY_DOWN)) {
-            buttons[0].state = BTN_STATE_HOLD;
-        } else {
-            buttons[0].state = BTN_STATE_RELEASED;
-        }
-        if (key_pressed(KEY_UP)) {
-            buttons[1].state = BTN_STATE_PRESSED;
-        } else if (key_hold(KEY_UP)) {
-            buttons[1].state = BTN_STATE_HOLD;
-        } else {
-            buttons[1].state = BTN_STATE_RELEASED;
-        }
-        if (key_pressed(KEY_LEFT)) {
-            buttons[2].state = BTN_STATE_PRESSED;
-        } else if (key_hold(KEY_LEFT)) {
-            buttons[2].state = BTN_STATE_HOLD;
-        } else {
-            buttons[2].state = BTN_STATE_RELEASED;
-        }
-        if (key_pressed(KEY_RIGHT)) {
-            buttons[3].state = BTN_STATE_PRESSED;
-        } else if (key_hold(KEY_RIGHT)) {
-            buttons[3].state = BTN_STATE_HOLD;
-        } else {
-            buttons[3].state = BTN_STATE_RELEASED;
-        }
-        if (key_pressed(KEY_L)) {
-            buttons[4].state = BTN_STATE_PRESSED;
-        } else if (key_hold(KEY_L)) {
-            buttons[4].state = BTN_STATE_HOLD;
-        } else {
-            buttons[4].state = BTN_STATE_RELEASED;
-        }
-        if (key_pressed(KEY_R)) {
-            buttons[5].state = BTN_STATE_PRESSED;
-        } else if (key_hold(KEY_R)) {
-            buttons[5].state = BTN_STATE_HOLD;
-        } else {
-            buttons[5].state = BTN_STATE_RELEASED;
-        }
-        if (key_pressed(KEY_A)) {
-            buttons[6].state = BTN_STATE_PRESSED;
-        } else if (key_hold(KEY_A)) {
-            buttons[6].state = BTN_STATE_HOLD;
-        } else {
-            buttons[6].state = BTN_STATE_RELEASED;
-        }
-        if (key_pressed(KEY_B)) {
-            buttons[7].state = BTN_STATE_PRESSED;
-        } else if (key_hold(KEY_B)) {
-            buttons[7].state = BTN_STATE_HOLD;
-        } else {
-            buttons[7].state = BTN_STATE_RELEASED;
-        }
-        if (key_pressed(KEY_START)) {
-            buttons[8].state = BTN_STATE_PRESSED;
-        } else if (key_hold(KEY_START)) {
-            buttons[8].state = BTN_STATE_HOLD;
-        } else {
-            buttons[8].state = BTN_STATE_RELEASED;
-        }
-        if (key_pressed(KEY_SELECT)) {
-            buttons[9].state = BTN_STATE_PRESSED;
-        } else if (key_hold(KEY_SELECT)) {
-            buttons[9].state = BTN_STATE_HOLD;
-        } else {
-            buttons[9].state = BTN_STATE_RELEASED;
-        }
-
         if (key_hold(KEY_DOWN)) {
             y += 3;
         }
@@ -1222,9 +56,7 @@ int main(void) {
         BG_H_SCROLL_0 = x;
         BG_V_SCROLL_0 = y;
 
-        for (size_t i = 0; i < sizeof(buttons) / sizeof(MultiSprite); ++i) {
-            button_tick(&buttons[i]);
-        }
+        update_button_sprites();
     };
 
     return 0;
diff --git a/src/sprites.h b/src/sprites.h
new file mode 100644
index 0000000..e7439f1
--- /dev/null
+++ b/src/sprites.h
@@ -0,0 +1,98 @@
+#ifndef GBAEXP_SPRITES_H
+#define GBAEXP_SPRITES_H
+
+#include "common.h"
+
+u32
+unpack_1bb(u8 hex) {
+    const u32 conversion_u32[16] = {
+        0x00000000, 0x00000001, 0x00000010, 0x00000011,
+        0x00000100, 0x00000101, 0x00000110, 0x00000111,
+        0x00001000, 0x00001001, 0x00001010, 0x00001011,
+        0x00001100, 0x00001101, 0x00001110, 0x00001111,
+    };
+    u8 low = hex & 0xF;
+    u8 high = (hex >> 4) & 0xF;
+    return (conversion_u32[high] << 16) | conversion_u32[low];
+}
+
+typedef struct Sprite {
+    // A unique sprite identifier.
+    size_t id;
+    // The number of tiles for a single sprite frame.
+    size_t n_tiles;
+    // The starting tile of this sprite.
+    size_t tile_start;
+    // The associated palette bank for this sprite.
+    size_t pal_bank;
+} Sprite;
+
+
+#define NUM_SPRITES 128
+Sprite sprites[NUM_SPRITES];
+
+// Keeping track of unique sprites and current sprite memory pointer using
+// global singletons.
+size_t sprite_counter = 0;
+size_t sprite_tile_counter = 0;
+u32 *sprite_memory = NULL;
+
+// Loads the sprite data into video memory and initialize the Sprite structure.
+size_t
+load_sprite_data(u32 *sprite_data, size_t n_tiles, size_t n_frames) {
+    memcpy(sprite_memory, sprite_data, 8 * n_tiles * n_frames * sizeof(u32));
+    sprite_memory += 8 * n_tiles * n_frames;
+    Sprite sprite = {
+        .id = sprite_counter,
+        .n_tiles = n_tiles,
+        .tile_start = sprite_tile_counter,
+    };
+    sprite_tile_counter += n_tiles * n_frames;
+    sprites[sprite_counter] = sprite;
+    return sprite_counter++;
+}
+
+size_t
+load_packed_sprite_data(u32 *sprite_data, size_t n_tiles, size_t n_frames) {
+    size_t counter = 0;
+    for (size_t i = 0; i < 8 * n_tiles * n_frames / 4; ++i) {
+        u32 hex = sprite_data[i];
+        sprite_memory[counter++] = unpack_1bb((hex >> 24) & 0xFF);
+        sprite_memory[counter++] = unpack_1bb((hex >> 16) & 0xFF);
+        sprite_memory[counter++] = unpack_1bb((hex >> 8) & 0xFF);
+        sprite_memory[counter++] = unpack_1bb((hex) & 0xFF);
+    }
+    sprite_memory += 8 * n_tiles * n_frames;
+    Sprite sprite = {
+        .id = sprite_counter,
+        .n_tiles = n_tiles,
+        .tile_start = sprite_tile_counter,
+    };
+    sprite_tile_counter += n_tiles * n_frames;
+    sprites[sprite_counter] = sprite;
+    return sprite_counter++;
+}
+
+void
+init_sprites(size_t starting_tile) {
+    // Initialize all attributes by disabling rendering. If we don't do this,
+    // glitches may appear.
+    for (size_t i = 0; i < 128; ++i) {
+        OBJ_ATTR_0(i) = (1 << 9);
+    }
+
+    sprite_counter = 0;
+    // Prepare global sprite_memory address.
+    sprite_memory = &TILE_MEM[4][starting_tile];
+}
+
+void
+init_sprite_pal(size_t starting_index, Color col) {
+    // Add colors to the sprite color palette. Tiles with color number 0 are
+    // treated as transparent.
+    for (size_t i = 0; i < 16; ++i) {
+        PAL_BUFFER_SPRITES[i + starting_index] = col;
+    }
+
+}
+#endif // GBAEXP_SPRITES_H