CoreGraphics line rendering performance bug

In general CoreGraphics is brutally fast, but I've been noticing some situations where it isn't which I narrowed down to non-uniform scaling of the CTM.

This program demonstrates how non-uniform scaling the CTM can adversely affect line rendering performance. It draws a grid of lines with scaling in X and Y adjustable by sliders and a rotate slider to get feedback on how fast it can render.

There's no voodoo here, the bottleneck is CGContextDrawPath(), drawing the grid scaled 0.5/0.6, or 0.2/0.5 on my MBP can take half a second, whereas if it is scaled 0.5/0.5 rendering is a couple orders of magnitude faster.

CTMScaleBug.zip

10.5.3