As reported by Ken Russell, TDL samples render a red background. The root cause of this issue is an incorrect color mask for a texture blit. Instead of all channels being blitted, ANGLE tries to blit only the colors present specified by glColorMask Blitting shouldn't be affected by the color mask.
Created attachment 416727 [details] Patch
Note that there are important steps to take when updating ANGLE. See https://trac.webkit.org/wiki/UpdatingANGLE
Comment on attachment 416727 [details] Patch Fantastic find and fix Kyle! Verified locally that this fixes the WebGL Aquarium with the Metal backend. r+
Comment on attachment 416727 [details] Patch Passed EWS; let me CQ this before the tree closure.
Committed r271080: <https://trac.webkit.org/changeset/271080> All reviewed patches have been landed. Closing bug and clearing flags on attachment 416727 [details].
<rdar://problem/72638743>