Vblank now returns a white screen if LCD is off, instead of keeping the buffer unmodified.

Core/display.c

@@ -3,6 +3,7 @@
 #include <sys/time.h>
 #include <stdlib.h>
 #include <assert.h>
+#include <string.h>
 #include "gb.h"
 #include "display.h"
 
@@ -197,6 +198,11 @@ void display_vblank(GB_gameboy_t *gb)
     frames++;
      */
 
+    if (!(gb->io_registers[GB_IO_LCDC] & 0x80)) {
+        /* LCD is off, memset screen to white */
+        memset(gb->screen, 0xFF, 160 * 144 * 4);
+    }
+
     gb->vblank_callback(gb);
     if (!gb->turbo) {
         struct timeval now;