Optionalsource_canvas: CanvasImageSourcea canvas source. defaults to getBGCanvas from the image module if none is provided
Optionalfps: numbernumber of times the popup canvas will be updated in a second
a popup window object with the ability to control the canvas through the DebugWindowCanvasControls interface
preview the offscreen canvas obtainable via getBGCanvas, on a separate popup debug window
alternatively, you can provide your own canvas source to preview on a separate popup debug window