v134 · graphics

OffscreenCanvas getContextAttributes

Add the getContextAttributes interface from CanvasRenderingContext2D to OffscreenCanvasRenderingContext2D.

concepts

  1. OffscreenCanvas getContextAttributes

    OffscreenCanvas exposes getContextAttributes() — useful for verifying alpha/colorSpace/willReadFrequently on a worker-thread context.

  2. Worker round-trip

    The motivating bug: request settings, transfer the canvas to a worker, ask the worker what attributes the engine actually granted. Side-by-side requested-vs-actual scoreboard.

  3. Attribute Lab

    Toggle every context attribute (alpha, colorSpace, desynchronized, willReadFrequently). Live table compares requested vs granted, with a sample render of the resulting bitmap.

  4. Image Pipeline

    Four-stage OffscreenCanvas pipeline (source → filter → composite → output). Each stage calls getContextAttributes() to verify alpha, colorSpace, and willReadFrequently were granted as requested — mismatches are flagged before the pipeline runs.

why it shipped

There is a lot of duplicated spec text for CanvasRenderingContext2D and OffscreenCanvasRenderingContext2D, especially related to how CanvasRenderingContext2DSettings is handled.

references