How to listen for internal render changes/requests

[ntadej]

Opening a discussion for now as it's more of a help request (and others may benefit). In Qt we need to listen for triggers to re-render the map. It seems in the past year or so scheduling got more advanced and probably I need to listen to some event. These are events that come from the style (such as opacity animation) and not events that come from user actions (such as panning or zooming).

[ntadej]

The issue was that the following mbgl::RendererObserver method needs to be reimplemented now:

    void onDidFinishRenderingFrame(RenderMode mode,
                                   bool repaintNeeded,
                                   bool placementChanged,
                                   const mbgl::gfx::RenderingStats& stats) final {
        void (mbgl::RendererObserver::*f)(RenderMode, bool, bool, const mbgl::gfx::RenderingStats&) =
            &mbgl::RendererObserver::onDidFinishRenderingFrame;
        delegate.invoke(f, mode, repaintNeeded, placementChanged, stats);
    }

FYI @adrian-cojocaru, we may want to make this more robust (potentially even remove variations of this method).