Decompile unref_sub_800D42C and add very likely explanation

1 files changed, 144 insertions, 0 deletions

diff --git a/src/decompress.c b/src/decompress.c
index d6c52439f..9f8916d52 100644
--- a/src/decompress.c
+++ b/src/decompress.c
@@ -111,3 +111,147 @@ void Unused_LZDecompressWramIndirect(const void **src, void *dest)
 {
     LZ77UnCompWram(*src, dest);
 }
+
+void unref_sub_800D42C(int object_size, int object_count, unsigned char *src_tiles, unsigned char *dest_tiles)
+{
+	/*
+	  This function appears to emulate behaviour found in the GB(C) versions regarding how the Pokemon images
+	  are stitched together to be displayed on the battle screen.
+	  Given "compacted" tiles, an object count and a bounding box/object size, place the tiles in such a way
+	  that the result will have each object centered in a 8x8 tile canvas.
+	*/
+	int i, j, k, l;
+	unsigned char *src = src_tiles, *dest = dest_tiles;
+	unsigned char bottom_off;
+
+	if (object_size & 1)
+	{
+		// Object size is odd
+		bottom_off = (object_size >> 1) + 4;
+		for (l = 0; l < object_count; l++)
+		{
+			// Clear all unused rows of tiles plus the half-tile required due to centering
+			for (j = 0; j < 8-object_size; j++)
+			{
+				for (k = 0; k < 8; k++)
+				{
+					for (i = 0; i < 16; i++)
+					{
+						if (j % 2 == 0)
+						{
+							// Clear top half of top tile and bottom half of bottom tile when on even j
+							((dest+i) + (k << 5))[((j >> 1) << 8)] = 0;
+							((bottom_off << 8) + (dest+i) + (k << 5) + 16)[((j >> 1) << 8)] = 0;
+						}
+						else
+						{
+							// Clear bottom half of top tile and top half of tile following bottom tile when on odd j
+							((dest+i) + (k << 5) + 16)[((j >> 1) << 8)] = 0;
+							((bottom_off << 8) + (dest+i) + (k << 5) + 256)[((j >> 1) << 8)] = 0;
+						}
+					}
+				}
+			}
+
+			// Clear the columns to the left and right that wont be used completely
+			// Unlike the previous loops, this will clear the later used space as well
+			for (j = 0; j < 2; j++)
+			{
+				for (i = 0; i < 8; i++)
+				{
+					for (k = 0; k < 32; k++)
+					{
+						// Left side
+						((dest+k) + (i << 8))[(j << 5)] = 0;
+						// Right side
+						((dest+k) + (i << 8))[(j << 5)+192] = 0;
+					}
+				}
+			}
+
+			// Skip the top row and first tile on the second row for objects of size 5
+			if (object_size == 5) dest += 0x120;
+
+			// Copy tile data
+			for (j = 0; j < object_size; j++)
+			{
+				for (k = 0; k < object_size; k++)
+				{
+					for (i = 0; i < 4; i++)
+					{
+						// Offset the tile by +4px in both x and y directions
+						(dest + (i << 2))[18] = (src + (i << 2))[0];
+						(dest + (i << 2))[19] = (src + (i << 2))[1];
+						(dest + (i << 2))[48] = (src + (i << 2))[2];
+						(dest + (i << 2))[49] = (src + (i << 2))[3];
+
+						(dest + (i << 2))[258] = (src + (i << 2))[16];
+						(dest + (i << 2))[259] = (src + (i << 2))[17];
+						(dest + (i << 2))[288] = (src + (i << 2))[18];
+						(dest + (i << 2))[289] = (src + (i << 2))[19];
+					}
+					src += 32;
+					dest += 32;
+				}
+
+				// At the end of a row, skip enough tiles to get to the beginning of the next row
+				if (object_size == 7) dest += 0x20;
+				else if (object_size == 5) dest += 0x60;
+			}
+
+			// Skip remaining unused space to go to the beginning of the next object
+			if (object_size == 7) dest += 0x100;
+			else if (object_size == 5) dest += 0x1e0;
+		}
+	}
+	else
+	{
+		// Object size is even
+		for (i = 0; i < object_count; i++)
+		{
+			// For objects of size 6, the first and last row and column will be cleared
+			// While the remaining space will be filled with actual data
+			if (object_size == 6)
+			{
+				for (k = 0; k < 256; k++) {
+					*dest = 0;
+					dest++;
+				}
+			}
+
+			for (j = 0; j < object_size; j++)
+			{
+				if (object_size == 6)
+				{
+					for (k = 0; k < 32; k++) {
+						*dest = 0;
+						dest++;
+					}
+				}
+
+				// Copy tile data
+				for (k = 0; k < 32 * object_size; k++) {
+					*dest = *src;
+					src++;
+					dest++;
+				}
+
+				if (object_size == 6)
+				{
+					for (k = 0; k < 32; k++) {
+						*dest = 0;
+						dest++;
+					}
+				}
+			}
+
+			if (object_size == 6)
+			{
+				for (k = 0; k < 256; k++) {
+					*dest = 0;
+					dest++;
+				}
+			}
+		}
+	}
+}