rasterStep

Runs step on the pixels of region under ctm, cut to the current clip. Some effects work on what was drawn, not on shapes: an SVG filter blurs or moves the pixels of an element (Filter Effects 1, 15), and a non-isolated transparency group takes the backdrop's part out of its own pixels before it composites (ISO 32000-1, 11.4.8). The step reads the backdrop, has content painted into rasters of the box through this canvas, works on them in plain Kotlin, and draws the result back, all through KiteRasterScope.

Returns true when the step ran, and also when nothing of region can show, which runs no step. Returns false when this canvas has no pixels to give or the step declined; the caller then draws its content without the step. A canvas that draws no pixels, such as one that collects text, keeps this default, which returns false, so it still sees the content.

Every paint the step makes through KiteRasterScope.render comes back through this canvas, so a wrapper that delegates with by sees those paints without overriding this.