Rendering.md

Rendering

This system needs a rework to get audio playback working

Video

Rendering uses SkiaSharp (for simplicity) and multiple render threads for speed. The RenderManager class handles the render initialisation.

The render phase is like this:

• Something tells the RenderManager that the render state is invalidated and to schedule a render on the app dispatcher
• All timeline tracks processed (bottom to top, as most editors do) to figure out if the track can be rendered (is it visible and a non-zero opacity and are there clips on the playhead that are visible)
• PrepareRenderFrame is called on the video tracks, which then calls PrepareRenderFrame on the clip being rendered. That method is used to generate rendering proxy data, such as the opacity of the clip at the current point in time
• A task is started, and that task calls the tracks' RenderFrame method, which calls the clips' RenderFrame method, which uses that proxy data (generated in the preparation phase) to actually draw pixels into the track's SKSurface
• Once all tracks have been rendered, the final frame is assembled from each track's SKSurface (on the rendering thread as well)
• The final frame is now completed, FrameRendered is fired in the render manager, and the view port hooks onto that event and draws the rendered frame

This is a simple but still performant rendering technique over say rendering all clips sequentially on the main thread (which is what I used to do). This may change in the future if I come up with a better system, but for now, it works pretty well

Audio

Audio playback is done via portaudio. Currently, it is sort of implemented but not active due to crackling issues