From 82ca58da04c954868172f226d7d977d7186c3ab7 Mon Sep 17 00:00:00 2001
From: amarcu5 <adampetermarcus@gmail.com>
Date: Mon, 14 Jan 2019 02:11:28 +0000
Subject: [PATCH] NSGL: Implement swap interval with CVDisplayLink

This fixes OpenGL swap interval (vsync) on macOS 10.14 Mojave by using
CVDisplayLink to synchronise to the monitor refresh rate rather than
setting NSOpenGLContextParameterSwapInterval.

Solution based on advice provided by @rcgordon.

Closes #1417.
---
 src/nsgl_context.h | 12 ++++++++--
 src/nsgl_context.m | 56 +++++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 60 insertions(+), 8 deletions(-)
 mode change 100644 => 100755 src/nsgl_context.h
 mode change 100644 => 100755 src/nsgl_context.m

diff --git a/src/nsgl_context.h b/src/nsgl_context.h
old mode 100644
new mode 100755
index 18042dee..76dd3e88
--- a/src/nsgl_context.h
+++ b/src/nsgl_context.h
@@ -27,13 +27,21 @@
 #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
 //
 typedef struct _GLFWcontextNSGL
 {
-    id           pixelFormat;
-    id	         object;
+    id                pixelFormat;
+    id	              object;
+    CVDisplayLinkRef  displayLink;
+    atomic_int        swapInterval;
+    int               swapIntervalsPassed;
+    id                swapIntervalCond;
 
 } _GLFWcontextNSGL;
 
diff --git a/src/nsgl_context.m b/src/nsgl_context.m
old mode 100644
new mode 100755
index f3bf2425..d834259d
--- a/src/nsgl_context.m
+++ b/src/nsgl_context.m
@@ -31,6 +31,27 @@
  #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)
 {
     @autoreleasepool {
@@ -48,21 +69,33 @@ static void makeContextCurrentNSGL(_GLFWwindow* window)
 static void swapBuffersNSGL(_GLFWwindow* window)
 {
     @autoreleasepool {
+
+    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];
+
     } // autoreleasepool
 }
 
 static void swapIntervalNSGL(int interval)
 {
     @autoreleasepool {
-
     _GLFWwindow* window = _glfwPlatformGetTls(&_glfw.contextSlot);
-
-    GLint sync = interval;
-    [window->context.nsgl.object setValues:&sync
-                              forParameter:NSOpenGLContextParameterSwapInterval];
-
+    atomic_store(&window->context.nsgl.swapInterval, interval);
+    [window->context.nsgl.swapIntervalCond lock];
+    window->context.nsgl.swapIntervalsPassed = 0;
+    [window->context.nsgl.swapIntervalCond unlock];
     } // autoreleasepool
 }
 
@@ -330,6 +363,17 @@ 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;
 }