rasterStep
open override fun rasterStep(region: KiteRectangle, ctm: KiteMatrix, step: KiteRasterStep): Boolean(source)
The raster step (#209, #308): its box is region under the canvas's matrix, cut to the device clip and rounded out to whole pixels. A render paints into a raster surface of the box. Skia reads back only the canvas under every layer, so inside a group's or a soft mask's layer the step gets no backdrop. Past MAX_STEP_PIXELS it works at a lower resolution, and then reads no backdrop either.