TextureMapper is used by GTK, WPE, WinCairo and PlayStation port. https://codepen.io/satoshi_hayashi/pen/poWwdmY It seems that there are two bugs, clip-path and -webkit-mask.
Created attachment 463444 [details] test case
Bug 241835 – TextureMapper: rendering issue of clip-path that is larger than the element Bug 219764 – [TextureMapper] Rotated mask layers don't clip descendent layers correctly
<rdar://problem/102301304>