- From: Simon Fraser via GitHub <sysbot+gh@w3.org>
- Date: Thu, 12 Jan 2017 17:12:04 +0000
- To: public-css-archive@w3.org
smfr has just created a new issue for https://github.com/w3c/csswg-drafts: == Reduce matrix decomposition when rotation axis has zero coord == http://www.w3.org/mid/CAGTfzwTS9r+z1LRu=3t25NW0A6yk0b+agaH6__8ZkcSD3-LR9A@mail.gmail.com Hi list, When interpolating between rotations with different axis alignment, we always fall back on matrix decomposition. However, if one of the angles is 0, then the resulting behavior is that the rotation axis snaps immediately to the other axis. So for example, if I transition transform: rotate3d(1, 0, 0, 0deg); to transform: rotate3d(0, 0, 1, 810deg); Then by the specification I should see a single 90deg rotation about the z axis. If I cancel and restart the transition, then the intermediate results (matrix) should force decomposition again and everything should be fairly consistent. Two things: (1) Firefox implements this behavior, but Chrome and Safari don't (try e.g. http://jsfiddle.net/2vLyydzv/3/). Chrome executes a 810deg rotation but messes up if you cancel/uncancel. Safari does something truly bizarre. (2) this is not compatible with the rotate property from css-transforms-2, as the rotate property can't have an intermediate result of a matrix and will instead take a rotation. That's fine for forward transforms but if I interpolate rotate: 0deg 1 0 0 to rotate: 810deg 0 0 1 then I'll have 45deg 0 0 1 at 50%. If I cancel, then rotate: 45deg 0 0 1 to rotate: 0deg 1 0 0 will be 22.5deg 0 0 1 at 50%. If I restart the transition, then rotate: 22.5deg 0 0 1 to rotate: 810deg 0 0 1 will do angle interpolation rather than matrix rotation, and start spinning wildly. Given the lack of conforming behavior in css-transforms-1, and (I believe) a desire for standardized behavior between css-transforms-1 and css-transforms-2, I'd like to propose that we special-case rotation to/from 0deg to always snap to the axis of the non-zero rotation and do numeric interpolation. This would reduce the cases in which we need to do matrix decomposition, not produce wildly variant behavior, better match author intention, and also make the rotate property capable of matching transform in behavior. Cheers, -Shane Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/897 using your GitHub account
Received on Thursday, 12 January 2017 17:12:10 UTC