SDL layer: don't call SDL_SetGammaRamp() if there would be no change.

This is in the similar vein as the set-palette deferring and it's this
that fixes the low FPS in the radioactively contaminated area in AMC TC:
Megabase (since setgamma() is called from setbrightness()).

Again, update issues might be expected, but changing focus between EDuke32
and the desktop and back seems to restore the gamma settings properly on
Kubuntu. Looks like X (or whatever above handles this stuff) maintains it
on a per-application basis.

git-svn-id: https://svn.eduke32.com/eduke32@2222 1a8010ca-5511-0410-912e-c29ae57300e0

polymer/eduke32/build/src/sdlayer.c

@@ -11,7 +11,7 @@
 #include "compat.h"
 #include "sdlayer.h"
 #include "cache1d.h"
-#include "pragmas.h"
+//#include "pragmas.h"
 #include "a.h"
 #include "build.h"
 #include "osd.h"
@@ -77,6 +77,9 @@ char nogl=0;
 #endif
 int32_t vsync=0;
 
+// last gamma, contrast, brightness
+static float lastvidgcb[3];
+
 //#define KEY_PRINT_DEBUG
 
 #if (SDL_MAJOR_VERSION == 1 && SDL_MINOR_VERSION < 3)
@@ -998,6 +1001,9 @@ int32_t setvideomode(int32_t x, int32_t y, int32_t c, int32_t fs)
     if (bpp > 8 && sdl_surface) polymost_glreset();
 #endif
 
+    // clear last gamma/contrast/brightness so that it will be set anew
+    lastvidgcb[0] = lastvidgcb[1] = lastvidgcb[2] = 0.0f;
+
     // restore gamma before we change video modes if it was changed
     if (sdl_surface && gammabrightness)
     {
@@ -1524,6 +1530,9 @@ int32_t setgamma(void)
 
     if (novideo) return 0;
 
+    if (lastvidgcb[0]==gamma && lastvidgcb[1]==contrast && lastvidgcb[2]==bright)
+        return 0;
+
     // This formula is taken from Doomsday
 
     for (i = 0; i < 256; i++)
@@ -1534,7 +1543,17 @@ int32_t setgamma(void)
 
         gammaTable[i] = gammaTable[i + 256] = gammaTable[i + 512] = (uint16_t)max(0.f,(double)min(0xffff,val*256));
     }
-    return SDL_SetGammaRamp(&gammaTable[0],&gammaTable[256],&gammaTable[512]);
+
+    i = SDL_SetGammaRamp(&gammaTable[0],&gammaTable[256],&gammaTable[512]);
+
+    if (i != -1)
+    {
+        lastvidgcb[0] = gamma;
+        lastvidgcb[1] = contrast;
+        lastvidgcb[2] = bright;
+    }
+
+    return i;
 }
 
 #ifndef __APPLE__