rasterStep
open override fun rasterStep(region: KiteRectangle, ctm: KiteMatrix, step: KiteRasterStep): Boolean(source)
The raster step (#209, #308): its box is region under ctm, which maps to this canvas's pixels, cut to the clip. A render paints into a bitmap of the box. Only a canvas over a known target bitmap reads a backdrop, and only outside every layer. Past STEP_MAX_PIXELS the step works at a lower resolution, and then reads no backdrop.