beginFrame
Prepare a frame for rendering and manage frame pacing.
Manages frame pacing and returns whether the frame should be rendered:
true: frame should be rendered; must call render() and endFrame().
false: frame is behind; can skip the frame (don't call endFrame()), or proceed anyway.
When false is returned, the application can either skip rendering the frame entirely, or proceed at the cost of increased latency.
Return
true if frame should be rendered, false if behind schedule.
Parameters
swapChain
SwapChain to render into.
frameTimeNanos
VSYNC time in steady_clock nanoseconds, or 0 to use setVsyncTime().