This stack overflow comment explains the problem well: http://stackoverflow.com/questions/19319963/how-to-avoid-seams-between-filled-areas-in-canvas This is a big problem for Shumway since all Flash shapes have disjoint fill areas and are subject to seaming. The problem gets worse when shapes are scaled down, seaming artifacts cause them to appear translucent. I'm speculating that drawing with anti-aliasing disabled can avoid seaming (I have no expertise in this area.)

Till says this is a hard problem with no workaround for Shumway, short of writing our own rasterizer. Not visible on most content, but some looks really bad for some scaled content. This is not a Shumway ship blocker. Examples of bad seams: http://people.mozilla.org/~jmuizelaar/p/part1.html http://codeazur.com.br/shumway/gl_tiger/ http://people.mozilla.org/~jmuizelaar/p/flower/full-bench-canvas.html https://dl.dropboxusercontent.com/u/55355076/full-scene-rasterizer-canvas/bird.html Expected results: http://people.mozilla.org/~jmuizelaar/p/flower/full-bench.html https://dl.dropboxusercontent.com/u/55355076/full-scene-rasterizer-js/bird.html