rasterStep
open override fun rasterStep(region: KiteRectangle, ctm: KiteMatrix, step: KiteRasterStep): Boolean(source)
The raster step (#209, #308): its box is region under ctm in device pixels, cut to the canvas that paints go to now. A render paints into an offscreen canvas of the box, as a group's layer does, and the backdrop comes from the canvas under the step, a layer or the page, through getImageData.