1691815 - Incorrect premultiplied alpha WebGL UNPACK for SVG images

Status: NEW

(Core :: Graphics: CanvasWebGL, defect)

Description

[jessevdk]

Attachment: test.html

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36

Steps to reproduce:

1. Create a basic WebGL application that renders a semi-transparent SVG square
2. Run application in Firefox on macOS
3. Run application in Chrome and Safari on macOS

Actual results:

The image renders darker than expected in Firefox (looking correct in Chrome and Safari). It looks like alpha has been pre-multiplied even though UNPACK_PREMULTIPLY_ALPHA_WEBGL was not specified (or set to false explicitly). When UNPACK_PREMULTIPLY_ALPHA_WEBGL is set to true, the image gets even darker, looking like alpha premultiplication was in effect applied twice.

Expected results:

The image should have rendered respecting the UNPACK_PREMULTIPLY_ALPHA_WEBGL setting.

Comment 1

[BugBot [:suhaib / :marco]]

The Bugbug bot thinks this bug should belong to the 'Core::Canvas: WebGL' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.