MGA: Implement gamma correction for 24+ bpp modes

src/include/86box/vid_svga.h

@@ -268,6 +268,9 @@ typedef struct svga_t {
     /* Pointer to monitor */
     monitor_t *monitor;
 
+    /* Enable LUT mapping of >= 24 bpp modes. */
+    int lut_map;
+
     void *  dev8514;
     void *  xga;
 } svga_t;

src/include/86box/video.h

@@ -32,6 +32,9 @@ using atomic_int  = std::atomic_int;
 
 #define makecol(r, g, b)   ((b) | ((g) << 8) | ((r) << 16))
 #define makecol32(r, g, b) ((b) | ((g) << 8) | ((r) << 16))
+#define getcolr(color) (((color) >> 16) & 0xFF)
+#define getcolg(color) (((color) >> 8) & 0xFF)
+#define getcolb(color) ((color) & 0xFF)
 
 enum {
     VID_NONE = 0,