Pokemon - Flickering SGB colors

[dobyrch]

Version: 9630583
OS: Arch Linux x86_64

In every SGB enhanced Pokemon game, the colors briefly flicker when starting a battle or switching Pokemon. The issue is caused by the ATTR_BLK command that sets the palette for the new Pokemon—it sets the palette outside of the block to 0, so the other Pokemon uses the wrong palette for a few frames until the next ATTR_BLK sets the correct palette.

Although it seems to be a mistake in the games' code, this capture of Pokemon Gold doesn't exhibit the issue.

I've been using the patch below to work around the bug, but I haven't tested it enough with other games to be certain that it doesn't break something else. This simply ignores any attempt to apply pallete 0 outside of the box specified by ATTR_BLK.

diff --git a/src/gb/renderers/software.c b/src/gb/renderers/software.c
index 25ca1f95..06cdbb0d 100644
--- a/src/gb/renderers/software.c
+++ b/src/gb/renderers/software.c
@@ -124,7 +124,7 @@ static void _parseAttrBlock(struct GBVideoSoftwareRenderer* renderer, int start)
                                        _setAttribute(renderer->d.sgbAttributes, x, y, pIn);
                                }
                        } else if (y < y0 || y > y1 || x < x0 || x > x1) {
-                               if (block[0] & 4) {
+                               if (block[0] & 4 && pOut) {
                                        _setAttribute(renderer->d.sgbAttributes, x, y, pOut);
                                }
                        } else {