When figure in a context with a scaling transformation matrix has a solid shadow, that shadow is rendered blurry in proportion to the magnitude of the scale. I believe what's happening here is that cairo is mask and stretching the edge. This can be observed by looking at fast/canvas/canvas-scale-fillPath-shadow.html. The solid shadow has a blurry edge.
Created attachment 145270 [details] Current result Martin, can you explain a bit more what you think goes wrong? Looking at the source of the test, line 56 has: ctx.shadowBlur = 10; So I believe, the two rightmost red rectangles are actually supposed to have blurry edges. I tested this with Debug GTKLauncher on r119211. So I can't see anything wrong here, we may close this issue.
Looks okay to me now too. Perhaps this was a bug in Cairo or was fixed by some other change!