From 8b37b4292a17c67a4711b90aa0e83d63acf26af6 Mon Sep 17 00:00:00 2001
From: GriffinR <griffin.g.richards@gmail.com>
Date: Tue, 9 May 2023 22:04:26 -0400
Subject: [PATCH] Document DrawFootprint

---
 include/gba/defines.h | 17 +++++++++++++----
 src/pokedex.c         | 40 +++++++++++++++++++++++++++-------------
 2 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/include/gba/defines.h b/include/gba/defines.h
index 82caf56e6..f2ea0899d 100644
--- a/include/gba/defines.h
+++ b/include/gba/defines.h
@@ -64,14 +64,23 @@
 
 #define ROM_HEADER_SIZE   0xC0
 
+// Dimensions of a tile in pixels
+#define TILE_WIDTH  8
+#define TILE_HEIGHT 8
+
+// Dimensions of the GBA screen in pixels
 #define DISPLAY_WIDTH  240
 #define DISPLAY_HEIGHT 160
 
-#define DISPLAY_TILE_WIDTH  (DISPLAY_WIDTH / 8)
-#define DISPLAY_TILE_HEIGHT (DISPLAY_HEIGHT / 8)
+// Dimensions of the GBA screen in tiles
+#define DISPLAY_TILE_WIDTH  (DISPLAY_WIDTH / TILE_WIDTH)
+#define DISPLAY_TILE_HEIGHT (DISPLAY_HEIGHT / TILE_HEIGHT)
 
-#define TILE_SIZE_4BPP 32
-#define TILE_SIZE_8BPP 64
+// Size of different tile formats in bytes
+#define TILE_SIZE(bpp)((bpp) * TILE_WIDTH * TILE_HEIGHT / 8)
+#define TILE_SIZE_1BPP TILE_SIZE(1) // 8
+#define TILE_SIZE_4BPP TILE_SIZE(4) // 32
+#define TILE_SIZE_8BPP TILE_SIZE(8) // 64
 
 #define TILE_OFFSET_4BPP(n) ((n) * TILE_SIZE_4BPP)
 #define TILE_OFFSET_8BPP(n) ((n) * TILE_SIZE_8BPP)
diff --git a/src/pokedex.c b/src/pokedex.c
index 88558d6f2..af96b8877 100644
--- a/src/pokedex.c
+++ b/src/pokedex.c
@@ -93,6 +93,13 @@ enum
     NAME_YZ,
 };
 
+enum {
+    WIN_INFO,
+    WIN_FOOTPRINT,
+    WIN_CRY_WAVE,
+    WIN_VU_METER,
+};
+
 // For scrolling search parameter
 #define MAX_SEARCH_PARAM_ON_SCREEN   6
 #define MAX_SEARCH_PARAM_CURSOR_POS  (MAX_SEARCH_PARAM_ON_SCREEN - 1)
@@ -888,11 +895,6 @@ static const struct BgTemplate sInfoScreen_BgTemplate[] =
     }
 };
 
-#define WIN_INFO 0
-#define WIN_FOOTPRINT 1
-#define WIN_CRY_WAVE 2
-#define WIN_VU_METER 3
-
 static const struct WindowTemplate sInfoScreen_WindowTemplates[] =
 {
     [WIN_INFO] =
@@ -4570,26 +4572,38 @@ static void PrintDecimalNum(u8 windowId, u16 num, u8 left, u8 top)
     PrintInfoSubMenuText(windowId, str, left, top);
 }
 
+// The footprints are drawn on WIN_FOOTPRINT, which uses BG palette 15 (loaded with graphics/text_window/message_box.gbapal)
+// The footprint pixels are stored as 1BPP, and set to the below color index in this palette when converted to 4BPP.
+#define FOOTPRINT_COLOR_IDX  2
+
+#define NUM_FOOTPRINT_TILES  4
+
 static void DrawFootprint(u8 windowId, u16 dexNum)
 {
-    u8 footprint[32 * 4];
+    u8 footprint4bpp[TILE_SIZE_4BPP * NUM_FOOTPRINT_TILES];
     const u8 * footprintGfx = gMonFootprintTable[NationalPokedexNumToSpecies(dexNum)];
     u16 tileIdx = 0;
     u16 i, j;
 
-    for (i = 0; i < 32; i++)
+    for (i = 0; i < TILE_SIZE_1BPP * NUM_FOOTPRINT_TILES; i++)
     {
-        u8 tile = footprintGfx[i];
+        u8 footprint1bpp = footprintGfx[i];
+
+        // Convert the 8 pixels in the above 1BPP byte to 4BPP.
+        // Each iteration creates one 4BPP byte (2 pixels),
+        // so we need 4 iterations to do all 8 pixels.
         for (j = 0; j < 4; j++)
         {
-            u8 value = ((tile >> (2 * j)) & 1 ? 2 : 0);
-            if (tile & (2 << (2 * j)))
-                value |= 0x20;
-            footprint[tileIdx] = value;
+            u8 tile = 0;
+            if (footprint1bpp & (1 << (2 * j)))
+                tile |= FOOTPRINT_COLOR_IDX; // Set pixel
+            if (footprint1bpp & (2 << (2 * j)))
+                tile |= FOOTPRINT_COLOR_IDX << 4; // Set pixel
+            footprint4bpp[tileIdx] = tile;
             tileIdx++;
         }
     }
-    CopyToWindowPixelBuffer(windowId, footprint, sizeof(footprint), 0);
+    CopyToWindowPixelBuffer(windowId, footprint4bpp, sizeof(footprint4bpp), 0);
 }
 
 // Unused Ruby/Sapphire function.