Fix glfwSetGamma generating ramps of invalid sizes

This makes glfwSetGamma generate a gamma ramp of the same size as the
monitor's current ramp, which will avoid failure on non-256 entry
monitors on X11 and avoid ramp interpolation on macOS.

Closes #1387.
Fixes #1388.

README.md

@@ -197,6 +197,8 @@ information on what to include when reporting a bug.
 - Bugfix: Invalid library paths were used in test and example CMake files (#930)
 - Bugfix: The scancode for synthetic key release events was always zero
 - Bugfix: The generated Doxyfile did not handle paths with spaces (#1081)
+- Bugfix: The gamma ramp generated by `glfwSetGamma` did not use the monitor
+          ramp size (#1387,#1388)
 - [Win32] Added system error strings to relevant GLFW error descriptions (#733)
 - [Win32] Moved to `WM_INPUT` for disabled cursor mode motion input (#125)
 - [Win32] Removed XInput circular deadzone from joystick axis data (#1045)

include/GLFW/glfw3.h

@@ -2156,9 +2156,9 @@ GLFWAPI const GLFWvidmode* glfwGetVideoMode(GLFWmonitor* monitor);
 
 /*! @brief Generates a gamma ramp and sets it for the specified monitor.
  *
- *  This function generates a 256-element gamma ramp from the specified exponent
- *  and then calls @ref glfwSetGammaRamp with it.  The value must be a finite
- *  number greater than zero.
+ *  This function generates an appropriately sized gamma ramp from the specified
+ *  exponent and then calls @ref glfwSetGammaRamp with it.  The value must be
+ *  a finite number greater than zero.
  *
  *  The software controlled gamma ramp is applied _in addition_ to the hardware
  *  gamma correction, which today is usually an approximation of sRGB gamma.
@@ -2237,8 +2237,8 @@ GLFWAPI const GLFWgammaramp* glfwGetGammaRamp(GLFWmonitor* monitor);
  *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED and @ref
  *  GLFW_PLATFORM_ERROR.
  *
- *  @remark Gamma ramp sizes other than 256 are not supported by all platforms
- *  or graphics hardware.
+ *  @remark The size of the specified gamma ramp should match the size of the
+ *  current ramp for that monitor.
  *
  *  @remark @win32 The gamma ramp size must be 256.
  *

src/monitor.c

@@ -427,9 +427,10 @@ GLFWAPI const GLFWvidmode* glfwGetVideoMode(GLFWmonitor* handle)
 
 GLFWAPI void glfwSetGamma(GLFWmonitor* handle, float gamma)
 {
-    int i;
-    unsigned short values[256];
+    unsigned int i;
+    unsigned short* values;
     GLFWgammaramp ramp;
+    const GLFWgammaramp* original;
     assert(handle != NULL);
     assert(gamma > 0.f);
     assert(gamma <= FLT_MAX);
@@ -442,12 +443,18 @@ GLFWAPI void glfwSetGamma(GLFWmonitor* handle, float gamma)
         return;
     }
 
-    for (i = 0;  i < 256;  i++)
+    original = glfwGetGammaRamp(handle);
+    if (!original)
+        return;
+
+    values = calloc(original->size, sizeof(unsigned short));
+
+    for (i = 0;  i < original->size;  i++)
     {
         float value;
 
         // Calculate intensity
-        value = i / 255.f;
+        value = i / (float) (original->size - 1);
         // Apply gamma curve
         value = powf(value, 1.f / gamma) * 65535.f + 0.5f;
         // Clamp to value range
@@ -459,9 +466,10 @@ GLFWAPI void glfwSetGamma(GLFWmonitor* handle, float gamma)
     ramp.red = values;
     ramp.green = values;
     ramp.blue = values;
-    ramp.size = 256;
+    ramp.size = original->size;
 
     glfwSetGammaRamp(handle, &ramp);
+    free(values);
 }
 
 GLFWAPI const GLFWgammaramp* glfwGetGammaRamp(GLFWmonitor* handle)