CameraView: sync pbo with glFence instead of calling glFinish (#23409)

* CameraView: sync pbo with glFence instead of calling glFinish (#23293)

* Sync pbo with fence

* use std::unique_ptr

* cameraview.cc: call glFlush after creating fence

Co-authored-by: Dean Lee <deanlee3@gmail.com>
old-commit-hash: d77782ea93

selfdrive/ui/qt/widgets/cameraview.cc

@@ -202,9 +202,15 @@ void CameraViewWidget::paintGL() {
   glClearColor(bg.redF(), bg.greenF(), bg.blueF(), bg.alphaF());
   glClear(GL_STENCIL_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
 
+  std::lock_guard lk(lock);
+
   if (latest_texture_id == -1) return;
 
   glViewport(0, 0, width(), height());
+  // sync with the PBO
+  if (wait_fence) {
+    wait_fence->wait();
+  }
 
   glBindVertexArray(frame_vao);
   glActiveTexture(GL_TEXTURE0);
@@ -289,6 +295,8 @@ void CameraViewWidget::vipcThread() {
     }
 
     if (VisionBuf *buf = vipc_client->recv(nullptr, 1000)) {
+      {
+        std::lock_guard lk(lock);
         if (!Hardware::EON()) {
           void *texture_buffer = gl_buffer->map(QOpenGLBuffer::WriteOnly);
           
@@ -305,10 +313,15 @@ void CameraViewWidget::vipcThread() {
           glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, buf->width, buf->height, GL_RGB, GL_UNSIGNED_BYTE, 0);
           glBindTexture(GL_TEXTURE_2D, 0);
           assert(glGetError() == GL_NO_ERROR);
-        // use glFinish to ensure that the texture has been uploaded.
-        glFinish();
+
+          wait_fence.reset(new WaitFence());
+
+          // Ensure the fence is in the GPU command queue, or waiting on it might block
+          // https://www.khronos.org/opengl/wiki/Sync_Object#Flushing_and_contexts
+          glFlush();
         }
         latest_texture_id = buf->idx;
+      }
       // Schedule update. update() will be invoked on the gui thread.
       QMetaObject::invokeMethod(this, "update");
 

selfdrive/ui/qt/widgets/cameraview.h

@@ -36,11 +36,20 @@ protected:
   virtual void updateFrameMat(int w, int h);
   void vipcThread();
 
+  struct WaitFence {
+    WaitFence() { sync = glFenceSync(GL_SYNC_GPU_COMMANDS_COMPLETE, 0); }
+    ~WaitFence() { glDeleteSync(sync); }
+    void wait() { glWaitSync(sync, 0, GL_TIMEOUT_IGNORED); }
+    GLsync sync = 0;
+  };
+
   bool zoomed_view;
-  std::atomic<int> latest_texture_id = -1;
+  std::mutex lock;
+  int latest_texture_id = -1;
   GLuint frame_vao, frame_vbo, frame_ibo;
   mat4 frame_mat;
   std::unique_ptr<EGLImageTexture> texture[UI_BUF_COUNT];
+  std::unique_ptr<WaitFence> wait_fence;
   std::unique_ptr<QOpenGLShaderProgram> program;
   QColor bg = QColor("#000000");
 
@@ -50,7 +59,6 @@ protected:
   std::atomic<VisionStreamType> stream_type;
   QThread *vipc_thread = nullptr;
 
-
 protected slots:
   void vipcConnected(VisionIpcClient *vipc_client);
 };