Add tile drawing function for the framebuffer

2 files changed, 79 insertions, 13 deletions

diff --git a/src/main.c b/src/main.c
index 6226bcd..913043a 100644
--- a/src/main.c
+++ b/src/main.c
@@ -13,7 +13,6 @@ WITH REGARD TO THIS SOFTWARE.
 
 #include "filesystem.c"
 #include "renderer.c"
-// #include "text.h"
 
 //
 // Config parameters.
@@ -65,16 +64,11 @@ int main(void) {
     irq_init();
     irs_set(IRQ_VBLANK, irs_stub);
 
-    draw_pixel(10, 0, 1);
-    draw_pixel(10, 1, 2);
-    draw_pixel(10, 2, 3);
-    draw_pixel(10, 3, 4);
-    draw_pixel( 0, 0, 1);
-    draw_pixel( 0, 1, 2);
-    draw_pixel( 0, 2, 3);
-    draw_pixel( 0, 3, 4);
-    txt_position(8, 8);
-    txt_printf("Hello world!");
+    Tile *tile = FONT_DATA;
+    tile += 'A';
+    draw_tile(0, 0, tile, true);
+    draw_tile(0, 4, tile, true);
+    draw_tile(4, 0, tile, true);
 
     // Main loop.
     PROF_INIT();
diff --git a/src/renderer.c b/src/renderer.c
index bd2c023..500cc78 100644
--- a/src/renderer.c
+++ b/src/renderer.c
@@ -46,12 +46,12 @@
 static u32 dirty_tiles[21] = {0};
 
 // TODO: Allow disable bound checking at compile time.
-#define BOUNDCHECK_SCREEN() if (x >= SCREEN_WIDTH || y >= SCREEN_HEIGHT) return;
+#define BOUNDCHECK_SCREEN(X,Y) if ((X) >= SCREEN_WIDTH || (Y) >= SCREEN_HEIGHT) return;
 
 IWRAM_CODE
 void
 draw_pixel(u16 x, u16 y, u8 color) {
-    BOUNDCHECK_SCREEN();
+    BOUNDCHECK_SCREEN(x, y);
 
     // Find row position for the given x/y coordinates.
     size_t tile_x = x / 8;
@@ -70,6 +70,78 @@ draw_pixel(u16 x, u16 y, u8 color) {
 
 IWRAM_CODE
 void
+draw_tile(u16 x, u16 y, Tile *tile, bool merge) {
+    BOUNDCHECK_SCREEN(x, y);
+
+    // Find row position for the given x/y coordinates.
+    size_t tile_x = x / 8;
+    size_t tile_y = y / 8;
+    size_t start_col = x % 8;
+    size_t start_row = y % 8;
+
+    // Get a pointer to the backbuffer and the tile row.
+    size_t pos = start_row + (tile_x + tile_y * 32) * 8;
+    u32 *backbuffer = &BACKBUF[pos];
+    u32 *row = tile;
+
+    // This will blend all colors weirdly if using tiles that contain colors
+    // higher than 1.
+    size_t shift_left = start_col * 4;
+    size_t shift_right = (8 - start_col) * 4;
+    u32 row_mask = merge ? 0 : 0xFFFFFFFF << shift_left;
+
+    // Draw the tiles. There are 4 possible cases:
+    //     1. The tile is exactly at the tile boundary.
+    //     2. The tile spans 2 tiles horizontally.
+    //     3. The tile spans 2 tiles vertically.
+    //     4. The tile spans 4 tiles.
+    if (start_col == 0 && start_row == 0) {
+        for (size_t i = 0; i < (8 - start_row); i++, backbuffer++) {
+            BOUNDCHECK_SCREEN(x, y + i);
+            backbuffer[0] = (backbuffer[0] & ~row_mask) | row[i];
+        }
+        dirty_tiles[tile_y] |= 1 << tile_x;
+    } else if (start_row == 0) {
+        for (size_t i = 0; i < 8; i++, backbuffer++) {
+            BOUNDCHECK_SCREEN(x, y + i);
+            backbuffer[0] = (backbuffer[0] & ~row_mask) | (row[i] << shift_left);
+            backbuffer[8] = (backbuffer[8] & row_mask) | (row[i] >> shift_right);
+        }
+        dirty_tiles[tile_y] |= 1 << tile_x;
+        dirty_tiles[tile_y] |= 1 << (tile_x + 1);
+    } else if (start_col == 0) {
+        for (size_t i = 0; i < (8 - start_row); i++, backbuffer++) {
+            BOUNDCHECK_SCREEN(x, y + i);
+            backbuffer[0] = (backbuffer[0] & ~row_mask) | row[i];
+        }
+        backbuffer += 8 * 31;
+        for (size_t i = (8 - start_row); i < 8; i++, backbuffer++) {
+            BOUNDCHECK_SCREEN(x, y + i);
+            backbuffer[0] = (backbuffer[0] & ~row_mask) | row[i];
+        }
+        dirty_tiles[tile_y] |= 1 << tile_x;
+        dirty_tiles[tile_y + 1] |= 1 << tile_x;
+    } else {
+        for (size_t i = 0; i < (8 - start_row); i++, backbuffer++) {
+            BOUNDCHECK_SCREEN(x, y + i);
+            backbuffer[0] = (backbuffer[0] & ~row_mask) | (row[i] << shift_left);
+            backbuffer[8] = (backbuffer[8] & row_mask) | (row[i] >> shift_right);
+        }
+        backbuffer += 8 * 31;
+        for (size_t i = (8 - start_row); i < 8; i++, backbuffer++) {
+            BOUNDCHECK_SCREEN(x, y + i);
+            backbuffer[0] = (backbuffer[0] & ~row_mask) | (row[i] << shift_left);
+            backbuffer[8] = (backbuffer[8] & row_mask) | (row[i] >> shift_right);
+        }
+        dirty_tiles[tile_y] |= 1 << tile_x;
+        dirty_tiles[tile_y] |= 1 << (tile_x + 1);
+        dirty_tiles[tile_y + 1] |= 1 << tile_x;
+        dirty_tiles[tile_y + 1] |= 1 << (tile_x + 1);
+    }
+}
+
+IWRAM_CODE
+void
 flip_buffer(void) {
     // Copy dirty tiles from the backbuffer to the frontbuffer.
     Tile *dst = FRONTBUF;