Monitor: factor out _glfwPlatformGetGammaRampSize

Factor out a helper function to retrieve current gamma ramp size out of
_glfwPlatformGetGammaRamp implementations on Cocoa and X11, and add a
trivial implementation for Windows.  No functional change.

src/cocoa_monitor.m

@@ -467,9 +467,14 @@ void _glfwPlatformGetVideoMode(_GLFWmonitor* monitor, GLFWvidmode *mode)
     CVDisplayLinkRelease(link);
 }
 
+int _glfwPlatformGetGammaRampSize(_GLFWmonitor* monitor)
+{
+    return CGDisplayGammaTableCapacity(monitor->ns.displayID);
+}
+
 void _glfwPlatformGetGammaRamp(_GLFWmonitor* monitor, GLFWgammaramp* ramp)
 {
-    uint32_t i, size = CGDisplayGammaTableCapacity(monitor->ns.displayID);
+    uint32_t i, size = _glfwPlatformGetGammaRampSize(monitor);
     CGGammaValue* values = calloc(size * 3, sizeof(CGGammaValue));
 
     CGGetDisplayTransferByTable(monitor->ns.displayID,

src/internal.h

@@ -611,6 +611,7 @@ void _glfwPlatformGetMonitorContentScale(_GLFWmonitor* monitor,
                                          float* xscale, float* yscale);
 GLFWvidmode* _glfwPlatformGetVideoModes(_GLFWmonitor* monitor, int* count);
 void _glfwPlatformGetVideoMode(_GLFWmonitor* monitor, GLFWvidmode* mode);
+int  _glfwPlatformGetGammaRampSize(_GLFWmonitor* monitor);
 void _glfwPlatformGetGammaRamp(_GLFWmonitor* monitor, GLFWgammaramp* ramp);
 void _glfwPlatformSetGammaRamp(_GLFWmonitor* monitor, const GLFWgammaramp* ramp);
 

src/null_monitor.c

@@ -58,6 +58,11 @@ void _glfwPlatformGetVideoMode(_GLFWmonitor* monitor, GLFWvidmode* mode)
 {
 }
 
+int _glfwPlatformGetGammaRampSize(_GLFWmonitor* monitor)
+{
+    return 0;
+}
+
 void _glfwPlatformGetGammaRamp(_GLFWmonitor* monitor, GLFWgammaramp* ramp)
 {
 }

src/win32_monitor.c

@@ -455,6 +455,11 @@ void _glfwPlatformGetVideoMode(_GLFWmonitor* monitor, GLFWvidmode* mode)
                   &mode->blueBits);
 }
 
+int _glfwPlatformGetGammaRampSize(_GLFWmonitor* monitor)
+{
+    return 256;
+}
+
 void _glfwPlatformGetGammaRamp(_GLFWmonitor* monitor, GLFWgammaramp* ramp)
 {
     HDC dc;

src/wl_monitor.c

@@ -180,6 +180,11 @@ void _glfwPlatformGetVideoMode(_GLFWmonitor* monitor, GLFWvidmode* mode)
     *mode = monitor->modes[monitor->wl.currentMode];
 }
 
+int _glfwPlatformGetGammaRampSize(_GLFWmonitor* monitor)
+{
+    return 0;
+}
+
 void _glfwPlatformGetGammaRamp(_GLFWmonitor* monitor, GLFWgammaramp* ramp)
 {
     _glfwInputError(GLFW_PLATFORM_ERROR,

src/x11_monitor.c

@@ -422,17 +422,28 @@ void _glfwPlatformGetVideoMode(_GLFWmonitor* monitor, GLFWvidmode* mode)
     }
 }
 
+int _glfwPlatformGetGammaRampSize(_GLFWmonitor* monitor)
+{
+    int size = 0;
+
+    if (_glfw.x11.randr.available && !_glfw.x11.randr.gammaBroken)
+        size = XRRGetCrtcGammaSize(_glfw.x11.display, monitor->x11.crtc);
+    else if (_glfw.x11.vidmode.available)
+        XF86VidModeGetGammaRampSize(_glfw.x11.display, _glfw.x11.screen, &size);
+
+    return size;
+}
+
 void _glfwPlatformGetGammaRamp(_GLFWmonitor* monitor, GLFWgammaramp* ramp)
 {
+    int size = _glfwPlatformGetGammaRampSize(monitor);
+
+    _glfwAllocGammaArrays(ramp, size);
+
     if (_glfw.x11.randr.available && !_glfw.x11.randr.gammaBroken)
     {
-        const size_t size = XRRGetCrtcGammaSize(_glfw.x11.display,
-                                                monitor->x11.crtc);
         XRRCrtcGamma* gamma = XRRGetCrtcGamma(_glfw.x11.display,
                                               monitor->x11.crtc);
-
-        _glfwAllocGammaArrays(ramp, size);
-
         memcpy(ramp->red,   gamma->red,   size * sizeof(unsigned short));
         memcpy(ramp->green, gamma->green, size * sizeof(unsigned short));
         memcpy(ramp->blue,  gamma->blue,  size * sizeof(unsigned short));
@@ -441,11 +452,6 @@ void _glfwPlatformGetGammaRamp(_GLFWmonitor* monitor, GLFWgammaramp* ramp)
     }
     else if (_glfw.x11.vidmode.available)
     {
-        int size;
-        XF86VidModeGetGammaRampSize(_glfw.x11.display, _glfw.x11.screen, &size);
-
-        _glfwAllocGammaArrays(ramp, size);
-
         XF86VidModeGetGammaRamp(_glfw.x11.display,
                                 _glfw.x11.screen,
                                 ramp->size, ramp->red, ramp->green, ramp->blue);