- From: Frédéric Wang via GitHub <sysbot+gh@w3.org>
- Date: Fri, 10 Apr 2020 06:37:10 +0000
- To: public-css-archive@w3.org
cc @emilio https://drafts.csswg.org/css-transforms-2/#processing-of-perspective-transformed-boxes normalizes homogeneous coordinates to (x′, y′, z′, 1) = (x/w, y/w, z/w, w/w) when w > 0. Why do we need a special case for w < 0? https://en.wikipedia.org/wiki/Homogeneous_coordinates says they represent exactly the same point, so not sure what is meant by "behind". Example 8 does not explain why it is "incorrect". For a trivial example, the image of (0, 0, 0, 1) by M and -M are respectively (tx, 0, 0, 1) and (-tx, 0, 0, -1) which are the same point in homogeneous coordinates, but the former is rendered and the latter hidden? Additionally, this is inconsistent with https://drafts.csswg.org/css-transforms-2/#decomposing-a-3d-matrix which starts by normalizing the transformation matrix, so M and -M are interpolated exactly the same way. Here is a basic example where the non-animated "Middle" text with negative w is not rendered by browsers but the animated "w < 0" text is rendered: https://people.igalia.com/fwang/negative-w.html -- GitHub Notification of comment by fred-wang Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/912#issuecomment-611901717 using your GitHub account
Received on Friday, 10 April 2020 06:37:14 UTC