Take into account the original gamma before applying gamma.

src/cocoa_gamma.m

@@ -48,12 +48,21 @@ void _glfwPlatformGetGammaRamp(GLFWgammaramp* ramp)
     CGGammaValue red[GLFW_GAMMA_RAMP_SIZE];
     CGGammaValue green[GLFW_GAMMA_RAMP_SIZE];
     CGGammaValue blue[GLFW_GAMMA_RAMP_SIZE];
-    CGGetDisplayTransferByTable(0, GLFW_GAMMA_RAMP_SIZE, red, green, blue, &sampleCount);
+    
+    // For now, don't support anything that is not GLFW_GAMMA_RAMP_SIZE
+    // i.e. 256. I don't think anyone would want to change the gamma on
+    // Mac anyway...
+    if (_glfwLibrary.originalRampSize != GLFW_GAMMA_RAMP_SIZE)
+        return;
+    
+    CGGetDisplayTransferByTable(CGMainDisplayID(), GLFW_GAMMA_RAMP_SIZE, red, green, blue,
+                                &sampleCount);
+
     for (i = 0; i < GLFW_GAMMA_RAMP_SIZE; i++)
     {
-        _glfwLibrary.currentRamp.red[i] = red[i] * 65535;
-        _glfwLibrary.currentRamp.green[i] = green[i] * 65535;
-        _glfwLibrary.currentRamp.blue[i] = blue[i] * 65535;
+        ramp->red[i] = red[i] * 65535;
+        ramp->green[i] = green[i] * 65535;
+        ramp->blue[i] = blue[i] * 65535;
     }
 }
 
@@ -65,15 +74,25 @@ void _glfwPlatformGetGammaRamp(GLFWgammaramp* ramp)
 void _glfwPlatformSetGammaRamp(const GLFWgammaramp* ramp)
 {
     int i;
+    int size = GLFW_GAMMA_RAMP_SIZE;
     CGGammaValue red[GLFW_GAMMA_RAMP_SIZE];
     CGGammaValue green[GLFW_GAMMA_RAMP_SIZE];
     CGGammaValue blue[GLFW_GAMMA_RAMP_SIZE];
-    for (i = 0; i < GLFW_GAMMA_RAMP_SIZE; i++)
+    
+    // For now, don't support anything that is not GLFW_GAMMA_RAMP_SIZE
+    // i.e. 256. I don't think anyone would want to change the gamma on
+    // Mac anyway...
+    if (_glfwLibrary.originalRampSize != GLFW_GAMMA_RAMP_SIZE)
+        return;
+    
+    // Convert to float & take the difference of the original gamma and
+    // the linear function.
+    for (i = 0; i < size; i++)
     {
-        red[i] = ((float)_glfwLibrary.currentRamp.red[i]) / 65535.0f;
-        blue[i] = ((float)_glfwLibrary.currentRamp.green[i]) / 65535.0f;
-        green[i] = ((float)_glfwLibrary.currentRamp.blue[i]) / 65535.0f;
+        red[i] = ramp->red[i] / 65535.f;
+        green[i] = ramp->green[i] / 65535.f;
+        blue[i] = ramp->blue[i] / 65535.f;
     }
-    CGSetDisplayTransferByTable(0, GLFW_GAMMA_RAMP_SIZE, red, green, blue);
+    CGSetDisplayTransferByTable(CGMainDisplayID(), GLFW_GAMMA_RAMP_SIZE, red, green, blue);
 }
 

src/cocoa_init.m

@@ -225,6 +225,10 @@ int _glfwPlatformInit(void)
     _glfwLibrary.NS.desktopMode =
 	    (NSDictionary*) CGDisplayCurrentMode(CGMainDisplayID());
 
+    // Save the original gamma ramp
+    _glfwLibrary.originalRampSize = CGDisplayGammaTableCapacity(CGMainDisplayID());
+    _glfwPlatformGetGammaRamp(&_glfwLibrary.originalRamp);
+    
     return GL_TRUE;
 }
 
@@ -235,7 +239,10 @@ int _glfwPlatformInit(void)
 int _glfwPlatformTerminate(void)
 {
     // TODO: Probably other cleanup
-
+    
+    // Restore the original gamma ramp
+    _glfwPlatformSetGammaRamp(&_glfwLibrary.originalRamp);
+    
     [NSApp setDelegate:nil];
     [_glfwLibrary.NS.delegate release];
     _glfwLibrary.NS.delegate = nil;

src/gamma.c

@@ -62,20 +62,34 @@ GLFWAPI void glfwSetGamma(float gamma)
     for (i = 0;  i < size;  i++)
     {
         float value = (float) i / ((float) (size - 1));
-
+        int diffRed, diffGreen, diffBlue, newRed, newGreen, newBlue, pow1;
+        
+        // Reference our gamma 1.0f
+        pow1 = value * 65535.f + 0.5;
+        
         // Apply gamma
         value = (float) pow(value, 1.f / gamma) * 65535.f + 0.5f;
-
+        
         // Clamp values
         if (value < 0.f)
             value = 0.f;
         else if (value > 65535.f)
             value = 65535.f;
-
-        // Set the gamma ramp values
-        ramp.red[i]   = (unsigned short) value;
-        ramp.green[i] = (unsigned short) value;
-        ramp.blue[i]  = (unsigned short) value;
+        
+        // Use original gamma as reference
+        diffRed   = _glfwLibrary.originalRamp.red[i] - pow1;
+        diffGreen = _glfwLibrary.originalRamp.green[i] - pow1;
+        diffBlue  = _glfwLibrary.originalRamp.blue[i] - pow1;
+        
+        // Calculate new values
+        newRed    = diffRed + (unsigned short) value;
+        newGreen  = diffGreen + (unsigned short) value;
+        newBlue   = diffBlue + (unsigned short) value;
+        
+        // Set the gamma ramp values (whilst clamping)
+        ramp.red[i]   = newRed > 65535 ? 65535 : newRed < 0 ? 0 : newRed;
+        ramp.green[i] = newGreen > 65535 ? 65535 : newGreen < 0 ? 0 : newGreen;
+        ramp.blue[i]  = newBlue > 65535 ? 65535 : newBlue < 0 ? 0 : newBlue;
     }
 
     glfwSetGammaRamp(&ramp);