Start decoupling of rendering from update passes

1 files changed, 78 insertions, 0 deletions

diff --git a/src/renderer_m0.c b/src/renderer_m0.c
index 8bd4263..00874ea 100644
--- a/src/renderer_m0.c
+++ b/src/renderer_m0.c
@@ -615,6 +615,84 @@ draw_icn(size_t x, size_t y, u8 *sprite, u8 clr, u8 flip_x, u8 flip_y) {
     dirty_tiles[tile_y] |= dirty;
 }
 
+IWRAM_CODE
+void
+draw_tile(size_t x, size_t y, Tile *tile, u8 clr) {
+    BOUNDCHECK_SCREEN(x, y);
+    size_t tile_x0 = x / 8;
+    size_t tile_x1 = (x + 7) / 8;
+    size_t tile_y = y / 8;
+    size_t start_col = x % 8;
+    size_t start_row = y % 8;
+    size_t shift_left = start_col * 4;
+    size_t shift_right = (8 - start_col) * 4;
+    u32 dirty = (1 << tile_x0) | (1 << tile_x1);
+    u32 *dst = &backbuf[start_row + (tile_x0 + tile_y * 32) * 8];
+    // 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;
+    u32 row_mask_left = 0xFFFFFFFF << shift_left;
+    u32 row_mask_right = 0xFFFFFFFF >> shift_right;
+
+    // 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++, dst++) {
+            BOUNDCHECK_SCREEN(x, y + i);
+            dst[0] = (dst[0] & ~row_mask_left) | row[i] * clr;
+        }
+        dirty_tiles[tile_y] |= 1 << tile_x0;
+    } else if (start_row == 0) {
+        for (size_t i = 0; i < 8; i++, dst++) {
+            BOUNDCHECK_SCREEN(x, y + i);
+            dst[0] = (dst[0] & ~row_mask_left) | (row[i] * clr << shift_left);
+            dst[8] = (dst[8] & ~row_mask_right) | (row[i] * clr >> shift_right);
+        }
+        dirty_tiles[tile_y] |= 1 << tile_x0;
+        dirty_tiles[tile_y] |= 1 << (tile_x0 + 1);
+    } else if (start_col == 0) {
+        for (size_t i = 0; i < (8 - start_row); i++, dst++) {
+            BOUNDCHECK_SCREEN(x, y + i);
+            dst[0] = (dst[0] & ~row_mask_left) | row[i] * clr;
+        }
+        dst += 8 * 31;
+        for (size_t i = (8 - start_row); i < 8; i++, dst++) {
+            BOUNDCHECK_SCREEN(x, y + i);
+            dst[0] = (dst[0] & ~row_mask_left) | row[i] * clr;
+        }
+        dirty_tiles[tile_y] |= 1 << tile_x0;
+        dirty_tiles[tile_y + 1] |= 1 << tile_x0;
+    } else {
+        for (size_t i = 0; i < (8 - start_row); i++, dst++) {
+            BOUNDCHECK_SCREEN(x, y + i);
+            dst[0] = (dst[0] & ~row_mask_left) | (row[i] * clr << shift_left);
+            dst[8] = (dst[8] & ~row_mask_right) | (row[i] * clr >> shift_right);
+        }
+        dst += 8 * 31;
+        for (size_t i = (8 - start_row); i < 8; i++, dst++) {
+            BOUNDCHECK_SCREEN(x, y + i);
+            dst[0] = (dst[0] & ~row_mask_left) | (row[i] * clr << shift_left);
+            dst[8] = (dst[8] & ~row_mask_right) | (row[i] * clr >> shift_right);
+        }
+        dirty_tiles[tile_y] |= 1 << tile_x0;
+        dirty_tiles[tile_y] |= 1 << (tile_x0 + 1);
+        dirty_tiles[tile_y + 1] |= 1 << tile_x0;
+        dirty_tiles[tile_y + 1] |= 1 << (tile_x0 + 1);
+    }
+}
+
 //
 // Flipping buffers/copying memory.
 //