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#include "shorthand.h"
#include "bd-font.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_CONTROL *((vu32*)(MEM_IO + 0x0000))
#define DISP_STATUS *((vu32*)(MEM_IO + 0x0004))
#define DISP_VCOUNT *((vu32*)(MEM_IO + 0x0006))
// Display modes.
#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
// Layers.
#define DISP_BG0 0x0100
#define DISP_BG1 0x0200
#define DISP_BG2 0x0400
#define DISP_BG3 0x0800
#define DISP_OBJ 0x1000
static inline void
set_display_mode(u16 value) {
*((vu32*)(MEM_IO + 0x0000)) = value;
}
// 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;
// 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 ((vu16*) MEM_VRAM)
//
// Colors.
//
static inline Color
rgb15(u32 red, u32 green, u32 blue ) {
return (blue << 10) | (green << 5) | red;
}
// Using bd-font, an 8x8 bitmap font.
static inline 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 inline 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 inline void
draw_line(int x0, int y0, int x1, int y1, Color clr) {
// Keep track of the coordinate for writing to the memory buffer.
int x = x0;
int y = y0;
// Normalize the drawing direction to always draw from (x0, y0)->(x1, y1)
int x_step = 1;
int y_step = 1;
int dx = x1 - x0;
int dy = y1 - y0;
if (x0 > x1) {
x_step = -1;
dx = x0 - x1;
}
if (y0 > y1) {
y_step = -1;
dy = y0 - y1;
}
// Precalculate line deltas.
int ddx = dx + dx;
int ddy = dy + dy;
// These variables are dependant on the slope. We can avoid considering
// separate cases for positive and negative slopes by using pointers to
// update the step in x or y.
int diff;
int diff_inc_a;
int diff_inc_b;
int n_steps;
int *a;
int *b;
int a_step;
int b_step;
if (dx >= dy) {
diff = ddy - dx;
diff_inc_a = ddy;
diff_inc_b = ddx;
n_steps = dx;
a = &x;
b = &y;
a_step = x_step;
b_step = y_step;
} else {
diff = ddx - dy;
diff_inc_a = ddx;
diff_inc_b = ddy;
n_steps = dy;
a = &y;
b = &x;
a_step = y_step;
b_step = x_step;
}
// Draw the line with Bresenham's algorithm.
for (size_t i = 0; i <= n_steps; ++i) {
FRAMEBUFFER[y][x] = clr;
*a += a_step;
diff += diff_inc_a;
if (diff > 0) {
*b += b_step;
diff -= diff_inc_b;
}
}
}
static inline void
wait_vsync() {
while(DISP_VCOUNT >= 160);
while(DISP_VCOUNT < 160);
}
//
// Main functions.
//
int main(void) {
set_display_mode(DISP_MODE_3 | DISP_BG2);
put_text(0, 0, rgb15(18, 0, 0), "\n\n\n\n");
draw_line(0, 0, 3, 8,rgb15(0, 30, 0));
draw_line(8, 0, 16, 8,rgb15(0, 0, 30));
draw_line(0, 0, 8, 3,rgb15(0, 0, 30));
draw_line(8, 0, 16, 8,rgb15(0, 0, 30));
// Testing a "rectangle"
draw_line(0, 0, 0, 7,rgb15(0, 0, 30));
draw_line(0, 0, 7, 0,rgb15(0, 30, 30));
draw_line(0, 7, 7, 7,rgb15(30, 0, 0));
draw_line(7, 0, 7, 7,rgb15(0, 30, 0));
draw_line(8, 7, 15, 0,rgb15(0, 0, 30));
char scanline_counter[16];
while(true) {
wait_vsync();
};
return 0;
}
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