From 5ecd28cdc66b4c16bf228bf0717e65453bf6bf4e Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Sat, 5 Dec 2020 18:41:44 -0800
Subject: [PATCH] GBA Video: Fix palette when being initialized mid-frame

---
 include/mgba/internal/gba/renderers/gl.h |  2 +-
 src/gba/renderers/gl.c                   | 13 ++++++-------
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/include/mgba/internal/gba/renderers/gl.h b/include/mgba/internal/gba/renderers/gl.h
index 2e0cc646c..2908e48d9 100644
--- a/include/mgba/internal/gba/renderers/gl.h
+++ b/include/mgba/internal/gba/renderers/gl.h
@@ -152,7 +152,7 @@ struct GBAVideoGLRenderer {
 	GLuint paletteTex;
 	uint16_t shadowPalette[GBA_VIDEO_VERTICAL_PIXELS][512];
 	int nextPalette;
-	int lastPalette;
+	int paletteDirtyScanlines;
 	bool paletteDirty;
 
 	GLuint vramTex;
diff --git a/src/gba/renderers/gl.c b/src/gba/renderers/gl.c
index 68e87c801..3969b4b05 100644
--- a/src/gba/renderers/gl.c
+++ b/src/gba/renderers/gl.c
@@ -931,7 +931,7 @@ void GBAVideoGLRendererReset(struct GBAVideoRenderer* renderer) {
 	glRenderer->dispcnt = 0x0080;
 	glRenderer->mosaic = 0;
 	glRenderer->nextPalette = 0;
-	glRenderer->lastPalette = GBA_VIDEO_VERTICAL_PIXELS - 1;
+	glRenderer->paletteDirtyScanlines = GBA_VIDEO_VERTICAL_PIXELS;
 	memset(glRenderer->shadowRegs, 0, sizeof(glRenderer->shadowRegs));
 	glRenderer->regsDirty = 0xFFFFFFFFFFFEULL;
 
@@ -965,11 +965,7 @@ void GBAVideoGLRendererWritePalette(struct GBAVideoRenderer* renderer, uint32_t
 	int g = M_G5(value) << 1;
 	g |= g >> 5;
 	int b = M_B5(value);
-	if (glRenderer->nextPalette) {
-		glRenderer->lastPalette = glRenderer->nextPalette - 1;
-	} else {
-		glRenderer->lastPalette = GBA_VIDEO_VERTICAL_PIXELS - 1;
-	}
+	glRenderer->paletteDirtyScanlines = GBA_VIDEO_VERTICAL_PIXELS;
 	glRenderer->shadowPalette[glRenderer->nextPalette][address >> 1] = (r << 11) | (g << 5) | b;
 }
 
@@ -1376,7 +1372,10 @@ void GBAVideoGLRendererDrawScanline(struct GBAVideoRenderer* renderer, int y) {
 	}
 	if (glRenderer->paletteDirty) {
 		memcpy(glRenderer->shadowPalette[glRenderer->nextPalette], glRenderer->shadowPalette[oldPalette], sizeof(glRenderer->shadowPalette[0]));
-		if (glRenderer->nextPalette == glRenderer->lastPalette) {
+		if (glRenderer->paletteDirtyScanlines > 0) {
+			--glRenderer->paletteDirtyScanlines;
+		}
+		if (!glRenderer->paletteDirtyScanlines) {
 			glRenderer->paletteDirty = false;
 			glActiveTexture(GL_TEXTURE0);
 			glBindTexture(GL_TEXTURE_2D, glRenderer->paletteTex);