Although I have no fundamental objection to the idea of rotation-independent shadow settings, my instinct is that this would be problematic to implement. Box shadows as spec'ed are simple paint operations, not 3D lighting effects. As Tab noted, rotations are applied after the painted layer has been generated. Although the browser could keep track of the net rotation that will be applied to an element, and then apply the reverse effect to the shadow, this would have performance impacts beyond the extra calculations. Animated transformations are optimized because the painted content does not change. For most cases (a 2D rotated shape with a solid border & background), you can get the desired effect with a drop-shadow filter on an un-transformed wrapper element. A drop-shadow might not have the best rendering performance currently, but it could be improved in future if implementations use GPU blur effects. If a future CSS spec introduces proper 3D lighting and shadow effects, that would also probably be applied via `filter`. Box-shadows, in contrast, do not affect containing boxes & stacking contexts, so would be more difficult to transfer to GPU effects. ~ABR
Received on Friday, 19 February 2016 15:43:16 UTC