Comment 64 for bug 80921

Enabling sub-pixel hinted text turns out to be far tricker than one naively expects. This is due to the number of intermediate layers through which PDF is rendered, all supporting just a single alpha channel. At the moment, the only way I can think of supporting sub-pixel hinted geometry (why just limit it to text ;-) is through the use of auxiliary alpha maps, i.e. we need to preserve per-component alpha through the entire render pipeline in order to composite correctly onto the destination framebuffer. Tricky, but not impossible.