Example: data:text/html,<!doctype html> <div style="-moz-transform: perspective(200px)"> <div style="-moz-transform: translatez(-100px); width:100px;height:100px;background:blue"> <script> var rect = document.querySelector("div>div").getBoundingClientRect(); alert(rect.top+','+rect.right+','+rect.bottom+','+rect.left) </script> This should alert "8,108,108,8", because in transform-style: flat mode, transforms don't accumulate. Chrome 18 dev and IE10 Developer Preview both alert this (or something slightly off in IE's case). Nightlies alert something way off, the same as transform-style: preserve-3d. Bug 724025 and bug 718809 are related. The patch for those does not fix this. I'll attach a patch in a moment.
Created attachment 595470 [details] [diff] [review] Patch v1 I'll request review when tests have passed.
Autoland Patchset: Patches: 595470 Branch: mozilla-central => try Destination: http://hg.mozilla.org/try/rev/8f473a21d905 Try run started, revision 8f473a21d905. To cancel or monitor the job, see: https://tbpl.mozilla.org/?tree=Try&rev=8f473a21d905
Comment on attachment 595470 [details] [diff] [review] Patch v1 Review of attachment 595470 [details] [diff] [review]: ----------------------------------------------------------------- Preemptive r+ from me
You need to check Preserves3D() on the child instead here. Preserves3DChildren() means that the parent intends to preserve-3d on it's children (has the transform-style: preserve-3d attribute), but this isn't necessarily applied. overflow:hidden clipping on the child can prevent this from happening, see the implementation of nsIFrame::Preserves3D().
Actually, ignore me, only clipping on the parent affects this. This should be fine.
Try run for 8f473a21d905 is complete. Detailed breakdown of the results available here: https://tbpl.mozilla.org/?tree=Try&rev=8f473a21d905 Results (out of 212 total builds): success: 176 warnings: 22 failure: 14 Builds (or logs if builds failed) available at: http://email@example.com