GPUCanvasConfiguration constructor
format should be GPU.getPreferredCanvasFormat's answer, usage a
bitwise or of GpuTextureUsage values — COPY_DST and not
RENDER_ATTACHMENT where presenting is a copy — and alphaMode is
"opaque" or "premultiplied".
Implementation
external factory GPUCanvasConfiguration({
GPUDevice device,
String format,
int usage,
String alphaMode,
});