Fixed zero refresh rate on some monitors.

src/cocoa_monitor.m

diff --git a/src/cocoa_monitor.m b/src/cocoa_monitor.m
index e7aec2b..8340280 100644
--- a/src/cocoa_monitor.m
+++ b/src/cocoa_monitor.m
@@ -31,6 +31,8 @@
 #include <limits.h>
 
 #include <IOKit/graphics/IOGraphicsLib.h>
+#include <IOKit/graphics/IOGraphicsLib.h>
+#include <CoreVideo/CVBase.h>
 
 
 // Get the name of the specified display
@@ -94,13 +96,21 @@
 
 // Convert Core Graphics display mode to GLFW video mode
 //
-static GLFWvidmode vidmodeFromCGDisplayMode(CGDisplayModeRef mode)
+static GLFWvidmode vidmodeFromCGDisplayMode(CGDisplayModeRef mode,
+                                            CVDisplayLinkRef link)
 {
     GLFWvidmode result;
     result.width = (int) CGDisplayModeGetWidth(mode);
     result.height = (int) CGDisplayModeGetHeight(mode);
     result.refreshRate = (int) CGDisplayModeGetRefreshRate(mode);
 
+    if (result.refreshRate == 0)
+    {
+        const CVTime time = CVDisplayLinkGetNominalOutputVideoRefreshPeriod(link);
+        if (!(time.flags & kCVTimeIsIndefinite))
+            result.refreshRate = (int) (time.timeScale / (double) time.timeValue);
+    }
+
     CFStringRef format = CGDisplayModeCopyPixelEncoding(mode);
 
     if (CFStringCompare(format, CFSTR(IO16BitDirectPixels), 0) == 0)
@@ -334,6 +344,9 @@
     CFArrayRef modes;
     CFIndex count, i;
     GLFWvidmode* result;
+    CVDisplayLinkRef link;
+
+    CVDisplayLinkCreateWithCGDisplay(monitor->ns.displayID, &link);
 
     modes = CGDisplayCopyAllDisplayModes(monitor->ns.displayID, NULL);
     count = CFArrayGetCount(modes);
@@ -348,21 +361,28 @@
         mode = (CGDisplayModeRef) CFArrayGetValueAtIndex(modes, i);
         if (modeIsGood(mode))
         {
-            result[*found] = vidmodeFromCGDisplayMode(mode);
+            result[*found] = vidmodeFromCGDisplayMode(mode, link);
             (*found)++;
         }
     }
 
     CFRelease(modes);
+
+    CVDisplayLinkRelease(link);
     return result;
 }
 
 void _glfwPlatformGetVideoMode(_GLFWmonitor* monitor, GLFWvidmode *mode)
 {
     CGDisplayModeRef displayMode;
+    CVDisplayLinkRef link;
+
+    CVDisplayLinkCreateWithCGDisplay(monitor->ns.displayID, &link);
 
     displayMode = CGDisplayCopyDisplayMode(monitor->ns.displayID);
-    *mode = vidmodeFromCGDisplayMode(displayMode);
+    *mode = vidmodeFromCGDisplayMode(displayMode, link);
     CGDisplayModeRelease(displayMode);
+
+    CVDisplayLinkRelease(link);
 }