gpu: added x direction support to VramToVram copy

Author: JaCzekanski

src/device/gpu/gpu.cpp

@@ -523,8 +523,15 @@ void GPU::cmdVramToVram() {
     int w = MaskCopy::w(arguments[3] & 0xffff);
     int h = MaskCopy::h((arguments[3] & 0xffff0000) >> 16);
 
+    // Note: VramToVram copy is always Top-to-Bottom
+    // but it might be Left-to-Right or Right-to-Left depending whether srcX < dstX
+    // See gpu/vram-to-vram-overlap test
+    bool dir = srcX < dstX;
+
     for (int y = 0; y < h; y++) {
-        for (int x = 0; x < w; x++) {
+        for (int _x = 0; _x < w; _x++) {
+            int x = (!dir) ? _x : w - 1 - _x;
+
             uint16_t src = VRAM[(srcY + y) % VRAM_HEIGHT][(srcX + x) % VRAM_WIDTH];
             maskedWrite(dstX + x, dstY + y, src);
         }