GBA Video: Implement green swap (fixes #1609)

CHANGES

@@ -42,6 +42,7 @@ Emulation fixes:
  - GBA Video: Fix Hblank timing
  - GBA Video: Invalidate map cache when modifying BGCNT (fixes mgba.io/i/1846)
  - GBA Video: Don't draw sprites using unmapped VRAM in GL renderer (fixes mgba.io/i/1865)
+ - GBA Video: Implement green swap (fixes mgba.io/i/1609)
  - SM83: Emulate HALT bug
 Other fixes:
  - 3DS: Redo video sync to be more precise

include/mgba/core/interface.h

@@ -36,6 +36,23 @@ typedef uint32_t color_t;
 #define M_RGB8_TO_BGR5(X) ((((X) & 0xF8) >> 3) | (((X) & 0xF800) >> 6) | (((X) & 0xF80000) >> 9))
 #define M_RGB8_TO_RGB5(X) ((((X) & 0xF8) << 7) | (((X) & 0xF800) >> 6) | (((X) & 0xF80000) >> 19))
 
+#ifndef COLOR_16_BIT
+#define M_COLOR_RED   0x000000FF
+#define M_COLOR_GREEN 0x0000FF00
+#define M_COLOR_BLUE  0x00FF0000
+#define M_COLOR_ALPHA 0xFF000000
+#elif defined(COLOR_5_6_5)
+#define M_COLOR_RED   0x001F
+#define M_COLOR_GREEN 0x07E0
+#define M_COLOR_BLUE  0xF800
+#define M_COLOR_ALPHA 0x0000
+#else
+#define M_COLOR_RED   0x001F
+#define M_COLOR_GREEN 0x03E0
+#define M_COLOR_BLUE  0x7C00
+#define M_COLOR_ALPHA 0x1000
+#endif
+
 #ifndef PYCPARSE
 static inline color_t mColorFrom555(uint16_t value) {
 #ifdef COLOR_16_BIT

include/mgba/internal/gba/renderers/video-software.h

@@ -114,6 +114,7 @@ struct GBAVideoSoftwareRenderer {
 	uint16_t bldy;
 
 	GBAMosaicControl mosaic;
+	bool greenswap;
 
 	struct WindowN {
 		struct GBAVideoWindowRegion h;

src/gba/io.c

@@ -341,7 +341,7 @@ void GBAIOInit(struct GBA* gba) {
 }
 
 void GBAIOWrite(struct GBA* gba, uint32_t address, uint16_t value) {
-	if (address < REG_SOUND1CNT_LO && (address > REG_VCOUNT || address == REG_DISPCNT)) {
+	if (address < REG_SOUND1CNT_LO && (address > REG_VCOUNT || address < REG_DISPSTAT)) {
 		value = gba->video.renderer->writeVideoRegister(gba->video.renderer, address, value);
 	} else {
 		switch (address) {

src/gba/renderers/video-software.c

@@ -122,6 +122,7 @@ static void GBAVideoSoftwareRendererReset(struct GBAVideoRenderer* renderer) {
 	softwareRenderer->oamMax = 0;
 
 	softwareRenderer->mosaic = 0;
+	softwareRenderer->greenswap = false;
 	softwareRenderer->nextY = 0;
 
 	softwareRenderer->objOffsetX = 0;
@@ -179,6 +180,9 @@ static uint16_t GBAVideoSoftwareRendererWriteVideoRegister(struct GBAVideoRender
 		softwareRenderer->dispcnt = value;
 		GBAVideoSoftwareRendererUpdateDISPCNT(softwareRenderer);
 		break;
+	case REG_GREENSWP:
+		softwareRenderer->greenswap = value & 1;
+		break;
 	case REG_BG0CNT:
 		value &= 0xDFFF;
 		GBAVideoSoftwareRendererWriteBGCNT(softwareRenderer, &softwareRenderer->bg[0], value);
@@ -389,9 +393,6 @@ static uint16_t GBAVideoSoftwareRendererWriteVideoRegister(struct GBAVideoRender
 	case REG_MOSAIC:
 		softwareRenderer->mosaic = value;
 		break;
-	case REG_GREENSWP:
-		mLOG(GBA_VIDEO, STUB, "Stub video register write: 0x%03X", address);
-		break;
 	default:
 		mLOG(GBA_VIDEO, GAME_ERROR, "Invalid video register: 0x%03X", address);
 	}
@@ -675,16 +676,30 @@ static void GBAVideoSoftwareRendererDrawScanline(struct GBAVideoRenderer* render
 		}
 	}
 
+	if (softwareRenderer->greenswap) {
+		for (x = 0; x < GBA_VIDEO_HORIZONTAL_PIXELS; x += 4) {
+			row[x] = softwareRenderer->row[x] & (M_COLOR_RED | M_COLOR_BLUE);
+			row[x] |= softwareRenderer->row[x + 1] & M_COLOR_GREEN;
+			row[x + 1] = softwareRenderer->row[x + 1] & (M_COLOR_RED | M_COLOR_BLUE);
+			row[x + 1] |= softwareRenderer->row[x] & M_COLOR_GREEN;
+			row[x + 2] = softwareRenderer->row[x + 2] & (M_COLOR_RED | M_COLOR_BLUE);
+			row[x + 2] |= softwareRenderer->row[x + 3] & M_COLOR_GREEN;
+			row[x + 3] = softwareRenderer->row[x + 3] & (M_COLOR_RED | M_COLOR_BLUE);
+			row[x + 3] |= softwareRenderer->row[x + 2] & M_COLOR_GREEN;
+
+		}
+	} else {
 #ifdef COLOR_16_BIT
-	for (x = 0; x < GBA_VIDEO_HORIZONTAL_PIXELS; x += 4) {
+		for (x = 0; x < GBA_VIDEO_HORIZONTAL_PIXELS; x += 4) {
-		row[x] = softwareRenderer->row[x];
+			row[x] = softwareRenderer->row[x];
-		row[x + 1] = softwareRenderer->row[x + 1];
+			row[x + 1] = softwareRenderer->row[x + 1];
-		row[x + 2] = softwareRenderer->row[x + 2];
+			row[x + 2] = softwareRenderer->row[x + 2];
-		row[x + 3] = softwareRenderer->row[x + 3];
+			row[x + 3] = softwareRenderer->row[x + 3];
-	}
+		}
 #else
-	memcpy(row, softwareRenderer->row, GBA_VIDEO_HORIZONTAL_PIXELS * sizeof(*row));
+		memcpy(row, softwareRenderer->row, GBA_VIDEO_HORIZONTAL_PIXELS * sizeof(*row));
 #endif
+	}
 }
 
 static void GBAVideoSoftwareRendererFinishFrame(struct GBAVideoRenderer* renderer) {