[HTML] 2D canvas floating point support

[ccameron-chromium]

I'm requesting a TAG review of 2D canvas floating point!

The output bitmap of a CanvasRenderingContext2D (or offscreen) defaults to being 8-bit on all browses (although it is not specified this way). This change makes that behavior explicitly specified, and add the option, via CanvasRenderingContext2DSettings, to specify that it can be 16-bit floating point.

• Explainer¹: canvas_float.md
• Specification: PR in development
• WPT Tests: In development
• User research: N/A
• Security and Privacy self-review²:
• GitHub repo:
• Primary contacts:
  • @ccameron-chromium, Chromium, co-author of specification
  • ColorWeb-CG
• Organization/project driving the specification: ColorWeb-CG
• Multi-stakeholder support³:
  • Chromium comments: None (author)
  • Mozilla comments: Canvas Floating Point Color Types mozilla/standards-positions#708
  • WebKit comments: Canvas Floating Point Color Types WebKit/standards-positions#91
• Status/issue trackers for implementations⁴:
  • Chromium: crbug.com/40277213

Further details:

• I have reviewed the TAG's Web Platform Design Principles
• Relevant time constraints or deadlines:
• The group where the work on this specification is currently being done: ColorWeb-CG
• Major unresolved issues with or opposition to this specification:
• This work is being funded by:

You should also know that...

A superset of this functionality was reviewed by TAG as part of the proposal for Adding support for High Dynamic Range (HDR) imagery to HTML Canvas. That proposal is being split into several independent components to be added individually.

[ccameron-chromium]

The comments for the larger TAG review that are relevant for this the ones relating to toDataURL and toBlob, which have been clarified (both in terms of immediate behavior and future extensions in HDR work) in the smaller explainer.