From cef3385c2bee0b098a7795548345a9281ace008e Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Wed, 26 Jul 2023 08:39:37 -0700
Subject: Add support for paletted sprites.

---
 gfx-iso/src/isogfx.c | 65 +++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 46 insertions(+), 19 deletions(-)

(limited to 'gfx-iso/src/isogfx.c')

diff --git a/gfx-iso/src/isogfx.c b/gfx-iso/src/isogfx.c
index 9ba1bec..4568375 100644
--- a/gfx-iso/src/isogfx.c
+++ b/gfx-iso/src/isogfx.c
@@ -100,26 +100,49 @@ static inline const Ts_Tile* ts_tileset_get_next_tile(
 /// The pixels of the row follow a "sprite-major" order. It contains the
 /// 'sprite_width * sprite_height' pixels for the first column/sprite, then the
 /// second column/sprite, etc.
+///
+/// Pixels are 8-bit indices into the sprite sheet's colour palette.
 typedef struct Ss_Row {
   uint16_t num_cols;  /// Number of columns in this row.
-  Pixel    pixels[1]; /// Count: num_cols * sprite_width * sprite_height.
+  uint8_t  pixels[1]; /// Count: num_cols * sprite_width * sprite_height.
 } Ss_Row;
 
+typedef struct Ss_Palette {
+  uint16_t num_colours;
+  Pixel    colours[1]; /// Count: num_colors.
+} Ss_Palette;
+
 /// Sprite sheet top-level data definition.
 ///
 /// Sprite width and height are assumed constant throughout the sprite sheet.
 typedef struct Ss_SpriteSheet {
-  uint16_t sprite_width;  /// Sprite width in pixels.
-  uint16_t sprite_height; /// Sprite height in pixels.
-  uint16_t num_rows;
-  Ss_Row   rows[1]; /// Count: num_rows.
+  uint16_t   sprite_width;  /// Sprite width in pixels.
+  uint16_t   sprite_height; /// Sprite height in pixels.
+  uint16_t   num_rows;
+  Ss_Palette palette; /// Variable size.
+  Ss_Row     rows[1]; /// Count: num_rows. Variable offset.
 } Ss_SpriteSheet;
 
-const Ss_Row* get_sprite_sheet_row(const Ss_SpriteSheet* sheet, int row) {
+static inline const Ss_Row* get_sprite_sheet_row(
+    const Ss_SpriteSheet* sheet, int row) {
   assert(sheet);
   assert(row >= 0);
   assert(row < sheet->num_rows);
-  return &sheet->rows[row];
+  // Skip over the palette.
+  const Ss_Row* rows =
+      (const Ss_Row*)(&sheet->palette.colours[0] + sheet->palette.num_colours);
+  return &rows[row];
+}
+
+static inline const uint8_t* get_sprite_sheet_sprite(
+    const Ss_SpriteSheet* sheet, const Ss_Row* row, int col) {
+  assert(sheet);
+  assert(row);
+  assert(col >= 0);
+  assert(col < row->num_cols);
+  const int sprite_offset = col * sheet->sprite_width * sheet->sprite_height;
+  const uint8_t* sprite   = &row->pixels[sprite_offset];
+  return sprite;
 }
 
 // -----------------------------------------------------------------------------
@@ -732,11 +755,19 @@ static Pixel alpha_blend(Pixel src, Pixel dst) {
 ///
 /// The rectangle's pixels are assumed to be arranged in a linear, row-major
 /// fashion.
+///
+/// If indices are given, then the image is assumed to be colour-paletted, where
+/// 'pixels' is the palette and 'indices' the pixel indices. Otherwise, the
+/// image is assumed to be in plain RGBA format.
 static void draw_rect(
     IsoGfx* iso, ivec2 origin, int rect_width, int rect_height,
-    const Pixel* pixels) {
+    const Pixel* pixels, const uint8_t* indices) {
   assert(iso);
 
+#define rect_pixel(x, y)                           \
+  (indices ? pixels[indices[py * rect_width + px]] \
+           : pixels[py * rect_width + px])
+
   // Rect can exceed screen bounds, so we must clip it.
 #define max(a, b) (a > b ? a : b)
   const int py_offset = max(0, rect_height - origin.y);
@@ -748,7 +779,7 @@ static void draw_rect(
     const int sy = origin.y + py - py_offset;
     for (int px = 0; (px < rect_width) && (origin.x + px < iso->screen_width);
          ++px) {
-      const Pixel colour = pixels[py * rect_width + px];
+      const Pixel colour = rect_pixel(px, py);
       if (colour.a > 0) {
         const int   sx              = origin.x + px;
         const Pixel dst             = screen_xy(iso, sx, sy);
@@ -767,7 +798,7 @@ static void draw_tile(IsoGfx* iso, ivec2 origin, Tile tile) {
 
   const Pixel* pixels = tile_xy_const_ref(iso, tile_data, 0, 0);
 
-  draw_rect(iso, origin, tile_data->width, tile_data->height, pixels);
+  draw_rect(iso, origin, tile_data->width, tile_data->height, pixels, 0);
 }
 
 static void draw(IsoGfx* iso) {
@@ -807,15 +838,11 @@ static void draw_sprite(
   assert(sprite->animation < sheet->num_rows);
   assert(sprite->frame >= 0);
 
-  const SpriteSheetRow* ss_row = &sheet->rows[sprite->animation];
-  assert(sprite->frame < ss_row->num_cols);
-
-  const int sprite_offset =
-      sprite->frame * sheet->sprite_width * sheet->sprite_height;
-
-  const Pixel* frame = &ss_row->pixels[sprite_offset];
-
-  draw_rect(iso, origin, sheet->sprite_width, sheet->sprite_height, frame);
+  const SpriteSheetRow* row = get_sprite_sheet_row(sheet, sprite->animation);
+  const uint8_t* frame = get_sprite_sheet_sprite(sheet, row, sprite->frame);
+  draw_rect(
+      iso, origin, sheet->sprite_width, sheet->sprite_height,
+      sheet->palette.colours, frame);
 }
 
 static void draw_sprites(IsoGfx* iso) {
-- 
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