Bug 1288626 will add the shape-outside support to the style system without considering animation. Let's complete the animation support here.

Per spec shape-outside [1] and clip-path [2] spec, both properties are animatable on <basic-shape> values, and we already support animation for clip-path on Gecko. To make shape-outisde animatable on Gecko, I think we'll need to make [3] eStyleAnimType_Custom, and refactor functions deal with StyleShapeSource in layout/style/StyleAnimationValue.cpp to support both clip-path and shape-outside. Boris Chiou (:boris) should know more animation part than I do. [1] https://drafts.csswg.org/css-shapes/#propdef-shape-outside [2] https://drafts.fxtf.org/css-masking-1/#the-clip-path [3] http://searchfox.org/mozilla-central/rev/3291398f10dcbe192fb52e74974b172616c018aa/layout/style/nsCSSPropList.h#3745

Comment on attachment 8910138 [details] Bug 1289049 Part 4 - Make <basic-shape> animatable for shape-outside for gecko style system. https://reviewboard.mozilla.org/r/181630/#review186966

Comment on attachment 8910137 [details] Bug 1289049 Part 3 - Add CSS_PROPERTY_STORES_CALC flag to "shape-outside" property. https://reviewboard.mozilla.org/r/181628/#review186968

Comment on attachment 8910135 [details] Bug 1289049 Part 1 - Use shape source instead of clip path in naming. https://reviewboard.mozilla.org/r/181624/#review186988

Comment on attachment 8910136 [details] Bug 1289049 Part 2 - Extract a helper function ExtractComputedValueFromShapeSource(). https://reviewboard.mozilla.org/r/181626/#review186994

Pushed by tlin@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/1d5f95ad941e Part 1 - Use shape source instead of clip path in naming. r=boris https://hg.mozilla.org/integration/autoland/rev/132a940e3e5f Part 2 - Extract a helper function ExtractComputedValueFromShapeSource(). r=boris https://hg.mozilla.org/integration/autoland/rev/92bb93a96a44 Part 3 - Add CSS_PROPERTY_STORES_CALC flag to "shape-outside" property. r=boris https://hg.mozilla.org/integration/autoland/rev/f599f522b02e Part 4 - Make <basic-shape> animatable for shape-outside for gecko style system. r=boris

https://hg.mozilla.org/mozilla-central/rev/1d5f95ad941e https://hg.mozilla.org/mozilla-central/rev/132a940e3e5f https://hg.mozilla.org/mozilla-central/rev/92bb93a96a44 https://hg.mozilla.org/mozilla-central/rev/f599f522b02e

I've documented this by adding a note to the shape-outside browser compat table and experimental features page: https://developer.mozilla.org/en-US/docs/Web/CSS/shape-outside#Browser_compatibility https://developer.mozilla.org/en-US/Firefox/Experimental_features#CSS I've not mentioned it yet in the rel notes because it is still preffed off by default.