Cocoa: Only create per-monitor display link once

The display link query is not specific to any particular display mode
and so only needs to be done once.

The next step is to replace the display link altogether by querying
IOKit directly, which is what the display link does.

src/cocoa_monitor.m

@@ -144,7 +144,7 @@ static GLFWbool modeIsGood(CGDisplayModeRef mode)
 // Convert Core Graphics display mode to GLFW video mode
 //
 static GLFWvidmode vidmodeFromCGDisplayMode(CGDisplayModeRef mode,
-                                            CVDisplayLinkRef link)
+                                            double fallbackRefreshRate)
 {
     GLFWvidmode result;
     result.width = (int) CGDisplayModeGetWidth(mode);
@@ -152,11 +152,7 @@ static GLFWvidmode vidmodeFromCGDisplayMode(CGDisplayModeRef mode,
     result.refreshRate = (int) round(CGDisplayModeGetRefreshRate(mode));
 
     if (result.refreshRate == 0)
-    {
+        result.refreshRate = (int) round(fallbackRefreshRate);
-        const CVTime time = CVDisplayLinkGetNominalOutputVideoRefreshPeriod(link);
-        if (!(time.flags & kCVTimeIsIndefinite))
-            result.refreshRate = (int) (time.timeScale / (double) time.timeValue);
-    }
 
 #if MAC_OS_X_VERSION_MAX_ALLOWED <= 101100
     CFStringRef format = CGDisplayModeCopyPixelEncoding(mode);
@@ -238,6 +234,29 @@ static GLFWbool refreshMonitorScreen(_GLFWmonitor* monitor)
     return GLFW_FALSE;
 }
 
+// Returns a fallback refresh rate for when Core Graphics says it is zero
+//
+static double getFallbackRefreshRate(_GLFWmonitor* monitor)
+{
+    CGDisplayModeRef mode = CGDisplayCopyDisplayMode(monitor->ns.displayID);
+    double refreshRate = CGDisplayModeGetRefreshRate(mode);
+    CGDisplayModeRelease(mode);
+
+    if (refreshRate == 0.0)
+    {
+        CVDisplayLinkRef link = NULL;
+        CVDisplayLinkCreateWithCGDisplay(monitor->ns.displayID, &link);
+
+        const CVTime time = CVDisplayLinkGetNominalOutputVideoRefreshPeriod(link);
+        if (!(time.flags & kCVTimeIsIndefinite))
+            refreshRate = (int) (time.timeScale / (double) time.timeValue);
+
+        CVDisplayLinkRelease(link);
+    }
+
+    return refreshRate;
+}
+
 
 //////////////////////////////////////////////////////////////////////////
 //////                       GLFW internal API                      //////
@@ -291,6 +310,7 @@ void _glfwPollMonitorsNS(void)
         _GLFWmonitor* monitor = _glfwAllocMonitor(name, size.width, size.height);
         monitor->ns.displayID  = displays[i];
         monitor->ns.unitNumber = unitNumber;
+        monitor->ns.fallbackRefreshRate = getFallbackRefreshRate(monitor);
 
         free(name);
 
@@ -318,9 +338,6 @@ void _glfwSetVideoModeNS(_GLFWmonitor* monitor, const GLFWvidmode* desired)
     if (_glfwCompareVideoModes(&current, best) == 0)
         return;
 
-    CVDisplayLinkRef link;
-    CVDisplayLinkCreateWithCGDisplay(monitor->ns.displayID, &link);
-
     CFArrayRef modes = CGDisplayCopyAllDisplayModes(monitor->ns.displayID, NULL);
     const CFIndex count = CFArrayGetCount(modes);
     CGDisplayModeRef native = NULL;
@@ -331,7 +348,8 @@ void _glfwSetVideoModeNS(_GLFWmonitor* monitor, const GLFWvidmode* desired)
         if (!modeIsGood(dm))
             continue;
 
-        const GLFWvidmode mode = vidmodeFromCGDisplayMode(dm, link);
+        const GLFWvidmode mode =
+            vidmodeFromCGDisplayMode(dm, monitor->ns.fallbackRefreshRate);
         if (_glfwCompareVideoModes(best, &mode) == 0)
         {
             native = dm;
@@ -350,7 +368,6 @@ void _glfwSetVideoModeNS(_GLFWmonitor* monitor, const GLFWvidmode* desired)
     }
 
     CFRelease(modes);
-    CVDisplayLinkRelease(link);
 }
 
 // Restore the previously saved (original) video mode
@@ -440,9 +457,6 @@ GLFWvidmode* _glfwPlatformGetVideoModes(_GLFWmonitor* monitor, int* count)
 
     *count = 0;
 
-    CVDisplayLinkRef link;
-    CVDisplayLinkCreateWithCGDisplay(monitor->ns.displayID, &link);
-
     CFArrayRef modes = CGDisplayCopyAllDisplayModes(monitor->ns.displayID, NULL);
     const CFIndex found = CFArrayGetCount(modes);
     GLFWvidmode* result = calloc(found, sizeof(GLFWvidmode));
@@ -453,7 +467,8 @@ GLFWvidmode* _glfwPlatformGetVideoModes(_GLFWmonitor* monitor, int* count)
         if (!modeIsGood(dm))
             continue;
 
-        const GLFWvidmode mode = vidmodeFromCGDisplayMode(dm, link);
+        const GLFWvidmode mode =
+            vidmodeFromCGDisplayMode(dm, monitor->ns.fallbackRefreshRate);
         CFIndex j;
 
         for (j = 0;  j < *count;  j++)
@@ -471,7 +486,6 @@ GLFWvidmode* _glfwPlatformGetVideoModes(_GLFWmonitor* monitor, int* count)
     }
 
     CFRelease(modes);
-    CVDisplayLinkRelease(link);
     return result;
 
     } // autoreleasepool
@@ -481,15 +495,10 @@ void _glfwPlatformGetVideoMode(_GLFWmonitor* monitor, GLFWvidmode *mode)
 {
     @autoreleasepool {
 
-    CVDisplayLinkRef link;
-    CVDisplayLinkCreateWithCGDisplay(monitor->ns.displayID, &link);
-
     CGDisplayModeRef native = CGDisplayCopyDisplayMode(monitor->ns.displayID);
-    *mode = vidmodeFromCGDisplayMode(native, link);
+    *mode = vidmodeFromCGDisplayMode(native, monitor->ns.fallbackRefreshRate);
     CGDisplayModeRelease(native);
 
-    CVDisplayLinkRelease(link);
-
     } // autoreleasepool
 }
 

src/cocoa_platform.h

@@ -170,6 +170,7 @@ typedef struct _GLFWmonitorNS
     CGDisplayModeRef    previousMode;
     uint32_t            unitNumber;
     id                  screen;
+    double              fallbackRefreshRate;
 
 } _GLFWmonitorNS;