Workaround for broken VSync in Simulate on macOS.

OpenGL VSync became broken again in macOS 13 (https://github.com/glfw/glfw/issues/2249). This workaround is similar to https://github.com/glfw/glfw/pull/2277 but is implemented entirely outside of GLFW.

PiperOrigin-RevId: 516320722
Change-Id: Ib8a651a942f592c74e00ad3c7b22f2dfd156be5f

doc/changelog.rst

@@ -33,6 +33,9 @@ Python bindings
 Simulate
 ^^^^^^^^
 
+- Implemented a workaround for `broken VSync <https://github.com/glfw/glfw/issues/2249>`_ on macOS so that the frame
+  rate is correctly capped when the Vertical Sync toggle is enabled.
+
 .. image:: images/changelog/contactlabel.png
    :align: right
    :width: 400px
@@ -42,6 +45,7 @@ Simulate
 
 |br|
 
+
 Version 2.3.2 (February 7, 2023)
 --------------------------------
 

simulate/CMakeLists.txt

@@ -108,6 +108,10 @@ target_sources(
   PRIVATE glfw_adapter.cc glfw_dispatch.cc platform_ui_adapter.cc
 )
 target_compile_options(platform_ui_adapter PUBLIC ${MUJOCO_SIMULATE_COMPILE_OPTIONS})
+if(APPLE)
+  target_sources(platform_ui_adapter PUBLIC glfw_corevideo.h PRIVATE glfw_corevideo.mm)
+  target_link_libraries(platform_ui_adapter PUBLIC "-framework CoreVideo")
+endif()
 target_include_directories(
   platform_ui_adapter PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}
                              $<TARGET_PROPERTY:glfw,INTERFACE_INCLUDE_DIRECTORIES>

simulate/glfw_adapter.cc

@@ -22,6 +22,10 @@
 #include <mujoco/mujoco.h>
 #include "glfw_dispatch.h"
 
+#ifdef __APPLE__
+#include "glfw_corevideo.h"
+#endif
+
 namespace mujoco {
 namespace {
 int MaybeGlfwInit() {
@@ -88,6 +92,12 @@ GlfwAdapter::GlfwAdapter() {
       });
   Glfw().glfwSetWindowRefreshCallback(
       window_, +[](GLFWwindow* window) {
+#ifdef __APPLE__
+        auto& core_video = GlfwAdapterFromWindow(window).core_video_;
+        if (core_video.has_value()) {
+          core_video->UpdateDisplayLink();
+        }
+#endif
         GlfwAdapterFromWindow(window).OnWindowRefresh();
       });
   Glfw().glfwSetWindowSizeCallback(
@@ -142,7 +152,16 @@ void GlfwAdapter::SetClipboardString(const char* text) {
 }
 
 void GlfwAdapter::SetVSync(bool enabled){
+#ifdef __APPLE__
+  Glfw().glfwSwapInterval(0);
+  if (enabled && !core_video_.has_value()) {
+    core_video_.emplace(window_);
+  } else if (!enabled && core_video_.has_value()) {
+    core_video_.reset();
+  }
+#else
   Glfw().glfwSwapInterval(enabled);
+#endif
 }
 
 void GlfwAdapter::SetWindowTitle(const char* title) {
@@ -154,7 +173,16 @@ bool GlfwAdapter::ShouldCloseWindow() const {
 }
 
 void GlfwAdapter::SwapBuffers() {
+#ifdef __APPLE__
+  if (core_video_.has_value()) {
+    core_video_->EnqueueSwap();
+    core_video_->WaitForSwap();
+  } else {
+    Glfw().glfwSwapBuffers(window_);
+  }
+#else
   Glfw().glfwSwapBuffers(window_);
+#endif
 }
 
 void GlfwAdapter::ToggleFullscreen() {

simulate/glfw_adapter.h

@@ -21,6 +21,11 @@
 #include <mujoco/mujoco.h>
 #include "platform_ui_adapter.h"
 
+#ifdef __APPLE__
+#include <optional>
+#include "glfw_corevideo.h"
+#endif
+
 namespace mujoco {
 class GlfwAdapter : public PlatformUIAdapter {
  public:
@@ -61,6 +66,12 @@ class GlfwAdapter : public PlatformUIAdapter {
   // store last window information when going to full screen
   std::pair<int, int> window_pos_;
   std::pair<int, int> window_size_;
+
+#ifdef __APPLE__
+  // Workaround for perpertually broken OpenGL VSync on macOS,
+  // most recently https://github.com/glfw/glfw/issues/2249.
+  std::optional<GlfwCoreVideo> core_video_;
+#endif
 };
 }  // namespace mujoco
 

simulate/glfw_corevideo.h

@@ -0,0 +1,56 @@
+// Copyright 2023 DeepMind Technologies Limited
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef MUJOCO_SIMULATE_GLFW_COREVIDEO_H_
+#define MUJOCO_SIMULATE_GLFW_COREVIDEO_H_
+
+#ifndef __APPLE__
+#error "This header only works on macOS."
+#endif
+
+#include <condition_variable>
+#include <mutex>
+
+#include "glfw_dispatch.h"
+
+#ifdef __OBJC__
+#import <CoreVideo/CoreVideo.h>
+#else
+typedef void* CVDisplayLinkRef;
+#endif
+
+// Workaround for perpertually broken OpenGL VSync on macOS,
+// most recently https://github.com/glfw/glfw/issues/2249.
+namespace mujoco {
+class GlfwCoreVideo {
+ public:
+  GlfwCoreVideo(GLFWwindow* window);
+  ~GlfwCoreVideo();
+  void EnqueueSwap();
+  void WaitForSwap();
+  int DisplayLinkCallback();
+  void UpdateDisplayLink();
+
+ private:
+  GLFWwindow* window_;
+  CVDisplayLinkRef display_link_;
+
+  bool second_buffer_has_content_;
+  std::mutex mu_;
+  std::condition_variable cond_;
+};
+}  // namespace mujoco
+
+
+#endif  // MUJOCO_SIMULATE_GLFW_COREVIDEO_H_

simulate/glfw_corevideo.mm

@@ -0,0 +1,75 @@
+// Copyright 2023 DeepMind Technologies Limited
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "glfw_corevideo.h"
+
+#include <condition_variable>
+#include <mutex>
+
+#include "glfw_adapter.h"
+#include "glfw_dispatch.h"
+
+// Workaround for perpertually broken OpenGL VSync on macOS,
+// most recently https://github.com/glfw/glfw/issues/2249.
+namespace mujoco {
+namespace {
+static int DisplayLinkCallbackTrampoline(CVDisplayLinkRef display_link,
+                                         const CVTimeStamp* now,
+                                         const CVTimeStamp* output_time,
+                                         CVOptionFlags flags_in,
+                                         CVOptionFlags* flags_out,
+                                         void* user_context) {
+  return static_cast<GlfwCoreVideo*>(user_context)->DisplayLinkCallback();
+}
+}  // namespace
+
+GlfwCoreVideo::GlfwCoreVideo(GLFWwindow* window) : window_(window) {
+  CVDisplayLinkCreateWithActiveCGDisplays(&display_link_);
+  CVDisplayLinkSetOutputCallback(display_link_, &DisplayLinkCallbackTrampoline, this);
+  CVDisplayLinkStart(display_link_);
+}
+
+GlfwCoreVideo::~GlfwCoreVideo() {
+  CVDisplayLinkStop(display_link_);
+  CVDisplayLinkRelease(display_link_);
+}
+
+void GlfwCoreVideo::EnqueueSwap() {
+  std::unique_lock lock(mu_);
+  second_buffer_has_content_ = true;
+}
+
+void GlfwCoreVideo::WaitForSwap() {
+  if (second_buffer_has_content_) {
+    std::unique_lock lock(mu_);
+    cond_.wait(lock, [this]() { return !this->second_buffer_has_content_; });
+  }
+}
+
+int GlfwCoreVideo::DisplayLinkCallback() {
+  if (second_buffer_has_content_) {
+    std::unique_lock lock(mu_);
+    Glfw().glfwSwapBuffers(window_);
+    second_buffer_has_content_ = false;
+    cond_.notify_one();
+  }
+  return kCVReturnSuccess;
+}
+
+void GlfwCoreVideo::UpdateDisplayLink() {
+  NSOpenGLContext* nsgl = Glfw().glfwGetNSGLContext(window_);
+  CVDisplayLinkSetCurrentCGDisplayFromOpenGLContext(display_link_, [nsgl CGLContextObj],
+                                                    [nsgl.pixelFormat CGLPixelFormatObj]);
+}
+}  // namespace mujoco

simulate/glfw_dispatch.cc

@@ -114,6 +114,10 @@ const struct Glfw& Glfw(void* dlhandle) {
     mjGLFW_INITIALIZE_SYMBOL(glfwWindowShouldClose);
     // go/keep-sorted end
 
+#ifdef __APPLE__
+    mjGLFW_INITIALIZE_SYMBOL(glfwGetNSGLContext);
+#endif
+
 #undef mjGLFW_INITIALIZE_SYMBOL
 
     return glfw;

simulate/glfw_dispatch.h

@@ -17,6 +17,11 @@
 
 #include <GLFW/glfw3.h>
 
+#ifdef __APPLE__
+#define GLFW_EXPOSE_NATIVE_NSGL
+#include <GLFW/glfw3native.h>
+#endif
+
 namespace mujoco {
 // Dynamic dispatch table for GLFW functions required by Simulate.
 // This allows us to use GLFW without introducing a link-time dependency on the
@@ -58,6 +63,11 @@ struct Glfw {
   mjGLFW_DECLARE_SYMBOL(glfwWindowHint);
   mjGLFW_DECLARE_SYMBOL(glfwWindowShouldClose);
   // go/keep-sorted end
+
+#ifdef __APPLE__
+  mjGLFW_DECLARE_SYMBOL(glfwGetNSGLContext);
+#endif
+
 #undef mjGLFW_DECLARE_SYMBOL
 };
 

simulate/simulate.cc

@@ -1950,6 +1950,9 @@ void Simulate::renderloop() {
   uiModify(&this->ui0, &this->uistate, &this->platform_ui->mjr_context());
   uiModify(&this->ui1, &this->uistate, &this->platform_ui->mjr_context());
 
+  // set VSync to initial value
+  this->platform_ui->SetVSync(this->vsync);
+
   // run event loop
   while (!this->platform_ui->ShouldCloseWindow() && !this->exitrequest.load()) {
     {