refresh SDL only when VRAM has changed, use default RGB masks on surf…

…ace creation

src/main.c

@@ -295,11 +295,7 @@ int main(int argc, char *argv[])
 		fprintf(stderr, "Error creating SDL texture: %s.\n", SDL_GetError());
 		exit(EXIT_FAILURE);
 	}
-    SDL_Surface *screen = SDL_CreateRGBSurface(0, 720, 348, 32,
-                                        0x00FF0000,
-                                        0x0000FF00,
-                                        0x000000FF,
-                                        0);
+    SDL_Surface *screen = SDL_CreateRGBSurface(0, 720, 348, 32, 0, 0, 0, 0);
 	if (!screen){
 		fprintf(stderr, "Error creating SDL surface: %s.\n", SDL_GetError());
 		exit(EXIT_FAILURE);
@@ -442,8 +438,11 @@ int main(int argc, char *argv[])
 		}
 		// Is it time to run the 60Hz periodic interrupt yet?
 		if (clock_cycles > CLOCKS_PER_60HZ) {
-			// Refresh the screen
-			refreshScreen(screen, renderer, texture);
+			// Refresh the screen if VRAM has been changed
+			if (state.vram_updated){
+				refreshScreen(screen, renderer, texture);
+				state.vram_updated = false;
+			}
 			if (state.timer_enabled){
 				m68k_set_irq(6);
 				state.timer_asserted = true;

src/memory.c

@@ -890,6 +890,7 @@ uint32_t m68k_read_memory_16(uint32_t address)/*{{{*/
 			case 0x020000:				// Video RAM
 				if (address > 0x427FFF) fprintf(stderr, "NOTE: RD16 from VideoRAM mirror, addr=0x%08X\n", address);
 				data = RD16(state.vram, address, 0x7FFF);
+				state.vram_updated = true;
 				break;
 			default:
 				data = IoRead(address, 16);

src/state.h

@@ -104,6 +104,9 @@ typedef struct {
 
 	/// VIDPAL mod (allows user writing to VRAM)
 	bool vidpal;
+
+	/// Update screen only when VRAM has been changed
+	bool vram_updated;
 } S_state;
 
 // Global emulator state. Yes, I know global variables are evil, please don't