GPU Display: Add vsync support for GLUT frontend

Author: davidrohr

GPU/GPUTracking/display/frontend/GPUDisplayFrontend.cxx

@@ -226,6 +226,11 @@ void GPUDisplayFrontend::applyInitialWindowState()
   }
 }
 
+bool GPUDisplayFrontend::vsyncEnabled() const
+{
+  return mDisplay->cfgR().drawQualityVSync;
+}
+
 int32_t& GPUDisplayFrontend::drawTextFontSize()
 {
   return mDisplay->drawTextFontSize();

GPU/GPUTracking/display/frontend/GPUDisplayFrontend.h

@@ -155,6 +155,7 @@ class GPUDisplayFrontend : public GPUDisplayFrontendInterface
   int32_t InitDisplay(bool initFailure = false);   // Callback to initialize the GL Display (to be called in StartDisplay)
   void ExitDisplay();                              // Callback to clean up the GL Display
   int32_t& drawTextFontSize();
+  bool vsyncEnabled() const;                            // VSync setting (drawQualityVSync)
   void setWindowState(bool fullScreen, bool maximized); // Sync the settings if the window manager changed the window state
   void focusLost();                                     // Release all keys and mouse buttons when the window loses focus, since the release events go to another window
   void applyInitialWindowState();                       // Switch to fullscreen / maximize at startup according to the settings

GPU/GPUTracking/display/frontend/GPUDisplayFrontendGlut.cxx

@@ -21,6 +21,10 @@
 #include <cstring>
 #include <GL/freeglut.h>
 #include <unistd.h>
+#ifdef GPUCA_BUILD_EVENT_DISPLAY_X11
+#include <GL/glx.h>
+#include <GL/glxext.h>
+#endif
 
 #include <pthread.h>
 using namespace o2::gpu;
@@ -264,6 +268,7 @@ int32_t GPUDisplayFrontendGlut::FrontendMain()
   glutPassiveMotionFunc(mouseMoveFunc);
   glutMouseWheelFunc(mMouseWheelFunc);
   applyInitialWindowState();
+  SetVSync(vsyncEnabled());
 
   {
     std::lock_guard lock(mExitStateMutex);
@@ -308,4 +313,12 @@ void GPUDisplayFrontendGlut::SwitchFullscreen(bool set)
 }
 
 void GPUDisplayFrontendGlut::ToggleMaximized(bool set) {}
-void GPUDisplayFrontendGlut::SetVSync(bool enable) {}
+void GPUDisplayFrontendGlut::SetVSync(bool enable) // GLUT has no swap interval API, set it via GLX directly (no-op if freeglut does not use GLX)
+{
+#ifdef GPUCA_BUILD_EVENT_DISPLAY_X11
+  auto swapInterval = (PFNGLXSWAPINTERVALEXTPROC)glXGetProcAddressARB((const GLubyte*)"glXSwapIntervalEXT");
+  if (swapInterval && glXGetCurrentDisplay()) {
+    swapInterval(glXGetCurrentDisplay(), glXGetCurrentDrawable(), enable);
+  }
+#endif
+}