preferences: add option to use glFinish

i hate opengl i hate opengl i hate opengl i hate opengl i hate opengl i hate opengl i hate opengl i hate opengl i hate opengl i hate opengl i hate opengl i hate opengl i hate opengl i hate opengl

app/config/config.cpp

@@ -104,6 +104,7 @@ void Config::SetDefaults()
   SetEntryInternal(QStringLiteral("UseLegacyColorInInputTab"), NodeValue::kBoolean, false);
   SetEntryInternal(QStringLiteral("ReassocLinToNonLin"), NodeValue::kBoolean, false);
   SetEntryInternal(QStringLiteral("PreviewNonFloatDontAskAgain"), NodeValue::kBoolean, false);
+  SetEntryInternal(QStringLiteral("UseGLFinish"), NodeValue::kBoolean, false);
 
   SetEntryInternal(QStringLiteral("TimelineThumbnailMode"), NodeValue::kInt, Timeline::kThumbnailInOut);
   SetEntryInternal(QStringLiteral("TimelineWaveformMode"), NodeValue::kInt, Timeline::kWaveformsEnabled);

app/dialog/preferences/tabs/preferencesbehaviortab.cpp

@@ -107,6 +107,11 @@ PreferencesBehaviorTab::PreferencesBehaviorTab()
           tr("Multiple clips can share the same nodes. Disable this to automatically share node "
              "dependencies among clips when copying or splitting them."),
           node_group);
+
+  QTreeWidgetItem* opengl_group = AddParent(tr("OpenGL"));
+  AddItem(tr("Use glFinish"),
+          QStringLiteral("UseGLFinish"),
+          opengl_group);
 }
 
 void PreferencesBehaviorTab::Accept(MultiUndoCommand *command)

app/render/opengl/openglrenderer.cpp

@@ -25,6 +25,8 @@
 #include <QDebug>
 #include <QOpenGLExtraFunctions>
 
+#include "config/config.h"
+
 namespace olive {
 
 const int OpenGLRenderer::kTextureCacheMaxSize = 5000;
@@ -364,7 +366,11 @@ void OpenGLRenderer::Flush()
 {
   GL_PREAMBLE;
 
-  functions_->glFlush();
+  if (OLIVE_CONFIG("UseGLFinish").toBool()) {
+    functions_->glFinish();
+  } else {
+    functions_->glFlush();
+  }
 }
 
 Color OpenGLRenderer::GetPixelFromTexture(Texture *texture, const QPointF &pt)