Notes on Hollowing Out the Black Shadows Over Unexplored Areas in Strategy Games

Carving a cutout (a circle or ellipse) out of a large dark shadow: once a sub-shape cache has been built, bitmap channel subtraction is cheaper than drawing a Shape with blend mode ERASE — but building that cache is costly, and the cost scales with the area of the region. So the two approaches each fit different cases. For large-area cutouts like drawing the border of a sphere of influence, blend-mode draw is probably the better choice.