workarounds: Add force frame sync option

The force frame sync option causes glFinish() to be called after
rendering but before commiting the new buffer. This can be used
to workaround driver bugs, especially where dma-fences are not
available for frame synchronization. This is the case with multi-
threaded llvmpipe rendering, using drm or wayland backends.

metadata/workarounds.xml

@@ -68,5 +68,10 @@
 			<_long>Enable certain damage optimizations which are based on a surfaces' opaque regions. In some cases, this optimization might give unexpected results (i.e background app stops updating) even though this is fine according to Wayland's protocol.</_long>
 			<default>false</default>
 		</option>
+		<option name="force_frame_sync" type="bool">
+			<_short>Force frame synchronization.</_short>
+			<_long>This option can be used to workaround driver bugs that cause rendering artifacts, though can cause more resource usage. Leave disabled if unsure.</_long>
+			<default>false</default>
+		</option>
 	</plugin>
 </wayfire>

src/output/render-manager.cpp

@@ -28,6 +28,7 @@ namespace wf
  */
 struct swapchain_damage_manager_t
 {
+    wf::option_wrapper_t<bool> force_frame_sync{"workarounds/force_frame_sync"};
     signal::connection_t<scene::root_node_update_signal> root_update;
     std::vector<scene::render_instance_uptr> render_instances;
 
@@ -341,6 +342,14 @@ struct swapchain_damage_manager_t
 
     void swap_buffers(std::unique_ptr<frame_object_t> next_frame, const wf::region_t& swap_damage)
     {
+        /* If force frame sync option is set, call glFinish to block until
+         * the GPU finishes rendering. This can work around some driver
+         * bugs, but may cause more resource usage. */
+        if (force_frame_sync)
+        {
+            GL_CALL(glFinish());
+        }
+
         frame_damage.clear();
 
         if (!wlr_render_pass_submit(next_frame->render_pass))