GB, GBA: Fix broken opposing button filter (fixes #1191)

CHANGES

@@ -109,6 +109,7 @@ Bugfixes:
  - GBA Video: Fix caching with background toggling (fixes mgba.io/i/1118)
  - Wii: Fix drawing caching regression (fixes mgba.io/i/1185)
  - Switch: Fix incorrect mapping for fast forward cap
+ - GB, GBA: Fix broken opposing button filter (fixes mgba.io/i/1191)
 Misc:
  - mGUI: Add SGB border configuration option
  - mGUI: Add support for different settings types

include/mgba/internal/gb/gb.h

@@ -117,6 +117,8 @@ struct GB {
 	bool earlyExit;
 	struct mTimingEvent eiPending;
 	unsigned doubleSpeed;
+
+	bool allowOpposingDirections;
 };
 
 struct GBCartridge {

src/gb/core.c

@@ -210,8 +210,12 @@ static void _GBCoreLoadConfig(struct mCore* core, const struct mCoreConfig* conf
 	mCoreConfigCopyValue(&core->config, config, "gb.model");
 	mCoreConfigCopyValue(&core->config, config, "sgb.model");
 	mCoreConfigCopyValue(&core->config, config, "cgb.model");
+	mCoreConfigCopyValue(&core->config, config, "allowOpposingDirections");
+
+	int fakeBool = 0;
+	mCoreConfigGetIntValue(config, "allowOpposingDirections", &fakeBool);
+	gb->allowOpposingDirections = fakeBool;
 
-	int fakeBool;
 	if (mCoreConfigGetIntValue(config, "sgb.borders", &fakeBool)) {
 		gb->video.sgbBorders = fakeBool;
 		gb->video.renderer->enableSGBBorder(gb->video.renderer, fakeBool);

src/gb/io.c

@@ -105,6 +105,7 @@ static const uint8_t _registerMask[] = {
 };
 
 static uint8_t _readKeys(struct GB* gb);
+static uint8_t _readKeysFiltered(struct GB* gb);
 
 static void _writeSGBBits(struct GB* gb, int bits) {
 	if (!bits) {
@@ -557,10 +558,26 @@ static uint8_t _readKeys(struct GB* gb) {
 	return gb->memory.io[REG_JOYP];
 }
 
+static uint8_t _readKeysFiltered(struct GB* gb) {
+	uint8_t keys = _readKeys(gb);
+	if (!gb->allowOpposingDirections && (keys & 0x30) == 0x20) {
+		unsigned rl = keys & 0x03;
+		unsigned ud = keys & 0x0C;
+		keys &= 0xF0;
+		if (rl != 0x03) {
+			keys |= rl;
+		}
+		if (ud != 0x0C) {
+			keys |= ud;
+		}
+	}
+	return keys;
+}
+
 uint8_t GBIORead(struct GB* gb, unsigned address) {
 	switch (address) {
 	case REG_JOYP:
-		return _readKeys(gb);
+		return _readKeysFiltered(gb);
 	case REG_IE:
 		return gb->memory.ie;
 	case REG_WAVE_0:

src/gba/core.c

@@ -239,6 +239,11 @@ static void _GBACoreLoadConfig(struct mCore* core, const struct mCoreConfig* con
 		}
 	}
 
+	int fakeBool = 0;
+	mCoreConfigGetIntValue(config, "allowOpposingDirections", &fakeBool);
+	gba->allowOpposingDirections = fakeBool;
+
+	mCoreConfigCopyValue(&core->config, config, "allowOpposingDirections");
 	mCoreConfigCopyValue(&core->config, config, "gba.bios");
 
 #ifndef DISABLE_THREADING