Render video effect one time for each frame in Grafika - CameraCaptureActivity

Question

I am referring to the demo app Grafika, in which the CameraCaptureActivity records a video while showing a live preview of the effects applied.

While recording in the CameraCaptureActivity, any effect that is applied to the frame that comes from the camera is done twice.
Once for the preview and once while saving the video to the file.

Since the same frame that is previewed is being saved to the file, it would save a lot of processing if this could be done just once.

The rendering of the frames happens directly on the two surfaces, one being the GLSurfaceView (for preview) and the other being MediaCodec (saving part).

Is there a way to render the OpenGL effect only once?

If I could copy the contents of one surface to the other it would be great.
Is there a way to do this?

Answer 1

Yes: you can render to an FBO, then blit the output twice, once for display and once for recording.

Grafika's "record GL app" activity demonstrates three different approaches to the problem (one of which only works on GLES 3.0+). The doFrame() method does the work; the draw-once-blit-twice approach is currently here.