macOS: Fix v-sync to monitor refresh rate no longer working under Mojave.

Mojave broke the technique GLFW used to use for v-sync. Changed to use
CVDisplayLink, fix comes from: https://github.com/glfw/glfw/pull/1417

docs/changelog.rst

@@ -56,6 +56,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 - macOS: When closing a top-level window only switch focus to the previous kitty
   window if it is on the same workspace (:iss:`1379`)
 
+- macOS: Fix v-sync to monitor refresh rate no longer working under Mojave. See
+  :opt:`sync_to_monitor`
+
 0.13.3 [2019-01-19]
 ------------------------------
 

glfw/nsgl_context.h

@@ -27,6 +27,8 @@
 #define _GLFW_PLATFORM_CONTEXT_STATE            _GLFWcontextNSGL nsgl
 #define _GLFW_PLATFORM_LIBRARY_CONTEXT_STATE    _GLFWlibraryNSGL nsgl
 
+#import <CoreVideo/CoreVideo.h>
+#include <stdatomic.h>
 
 // NSGL-specific per-context data
 //
@@ -34,6 +36,10 @@ typedef struct _GLFWcontextNSGL
 {
     id           pixelFormat;
     id           object;
+    CVDisplayLinkRef  displayLink;
+    atomic_int        swapInterval;
+    int               swapIntervalsPassed;
+    id                swapIntervalCond;
 
 } _GLFWcontextNSGL;
 
@@ -53,4 +59,3 @@ GLFWbool _glfwCreateContextNSGL(_GLFWwindow* window,
                                 const _GLFWctxconfig* ctxconfig,
                                 const _GLFWfbconfig* fbconfig);
 void _glfwDestroyContextNSGL(_GLFWwindow* window);
-

glfw/nsgl_context.m

@@ -32,6 +32,27 @@
  #define NSOpenGLContextParameterSurfaceOpacity NSOpenGLCPSurfaceOpacity
 #endif
 
+static CVReturn displayLinkCallback(CVDisplayLinkRef displayLink,
+                                    const CVTimeStamp* now,
+                                    const CVTimeStamp* outputTime,
+                                    CVOptionFlags flagsIn,
+                                    CVOptionFlags* flagsOut,
+                                    void* userInfo)
+{
+   _GLFWwindow* window = (_GLFWwindow *) userInfo;
+
+   const int setting = atomic_load(&window->context.nsgl.swapInterval);
+   if (setting > 0)
+   {
+       [window->context.nsgl.swapIntervalCond lock];
+       window->context.nsgl.swapIntervalsPassed++;
+       [window->context.nsgl.swapIntervalCond signal];
+       [window->context.nsgl.swapIntervalCond unlock];
+   }
+
+   return kCVReturnSuccess;
+}
+
 static void makeContextCurrentNSGL(_GLFWwindow* window)
 {
     if (window)
@@ -44,6 +65,18 @@ static void makeContextCurrentNSGL(_GLFWwindow* window)
 
 static void swapBuffersNSGL(_GLFWwindow* window)
 {
+
+    const int setting = atomic_load(&window->context.nsgl.swapInterval);
+    if (setting > 0)
+    {
+        [window->context.nsgl.swapIntervalCond lock];
+        do
+        {
+            [window->context.nsgl.swapIntervalCond wait];
+        } while (window->context.nsgl.swapIntervalsPassed % setting != 0);
+        window->context.nsgl.swapIntervalsPassed = 0;
+        [window->context.nsgl.swapIntervalCond unlock];
+    }
     // ARP appears to be unnecessary, but this is future-proof
     [window->context.nsgl.object flushBuffer];
 }
@@ -52,9 +85,11 @@ static void swapIntervalNSGL(int interval)
 {
     _GLFWwindow* window = _glfwPlatformGetTls(&_glfw.contextSlot);
 
-    GLint sync = interval;
+    atomic_store(&window->context.nsgl.swapInterval, interval);
-    [window->context.nsgl.object setValues:&sync
+    [window->context.nsgl.swapIntervalCond lock];
-                              forParameter:NSOpenGLContextParameterSwapInterval];
+    window->context.nsgl.swapIntervalsPassed = 0;
+
+    [window->context.nsgl.swapIntervalCond unlock];
 }
 
 static int extensionSupportedNSGL(const char* extension)
@@ -316,6 +351,18 @@ GLFWbool _glfwCreateContextNSGL(_GLFWwindow* window,
     window->context.getProcAddress = getProcAddressNSGL;
     window->context.destroy = destroyContextNSGL;
 
+    CVDisplayLinkCreateWithActiveCGDisplays(&window->context.nsgl.displayLink);
+    CVDisplayLinkSetOutputCallback(window->context.nsgl.displayLink,
+                                   &displayLinkCallback,
+                                   window);
+    CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext(
+            window->context.nsgl.displayLink,
+            (CGLContextObj)window->context.nsgl.object,
+            (CGLPixelFormatObj)window->context.nsgl.pixelFormat);
+    CVDisplayLinkStart(window->context.nsgl.displayLink);
+
+    window->context.nsgl.swapIntervalCond = [NSCondition new];
+
     return GLFW_TRUE;
 }