WebGL state reads back what the page just set
STENCIL_WRITEMASK, STENCIL_VALUE_MASK and COLOR_CLEAR_VALUE read back 15, 51 and [0.25, 0.5, 0.75, 1] after the page sets them (severity: warn).
What a detector infers
Some WebGL parameters are not capabilities but state the page itself controls. After stencilMask(0x0f), STENCIL_WRITEMASK must read 15; after stencilFunc(ALWAYS, 0, 0x33), STENCIL_VALUE_MASK must read 51; after clearColor(0.25, 0.5, 0.75, 1), COLOR_CLEAR_VALUE must read exactly that back. The specification defines these as the values last set, so the right answer is known before asking, with no reference data at all.
A getParameter hook that answers from a captured table of another machine's parameters has no notion of state: it returns whatever the table holds — typically the defaults the capture was taken with, stencil masks of 4294967295 and a clear colour of 0, 0, 0, 0 — whatever the page has just done. Measured on every stock browser tested: 15, 51 and 0.25, 0.5, 0.75, 1. The failing side was a table-replay spoof written for this test rather than a captured tool.
No ordinary configuration is known to break it; it is state the page sets and reads back in the same breath.
How to resolve it
Leave getParameter to the implementation. A table can describe limits, but not state the page has just changed; any wrapper has to pass state queries through to the real context.
Nearby checks in Render & GPU
- Grey drawing reads back as grey
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d3d-renderer-only-on-windowsDirect3D is a Windows API. ANGLE, the layer Chromium renders WebGL through, only names it in the unmasked renderer string when it is running… - A Direct3D 11 renderer reports the caps ANGLE's D3D11 backend fixes
webgl-d3d11-fixed-capsWhen ANGLE runs WebGL on Direct3D 11 at feature level 11 — the renderer string reads Direct3D11 vs_5_0 ps_5_0 — it does not ask the driver… - Every extension WebGL hands out is one it advertises
webgl-gettable-is-advertisedIn Chrome, getSupportedExtensions() and getExtension() read the same set: an extension the context can hand out is one it lists, and one it… - readPixels writes only the pixels it was asked to read
webgl-readpixels-sentinelreadPixels writes into an array the page supplies, and the WebGL specification is precise about the edges: when the requested rectangle… - A worker OffscreenCanvas encodes the pixels it reads back
offscreen-canvas-exits-agreeA canvas has more than one way out. getImageData hands pixels straight to script; convertToBlob encodes the same pixels into a file, and… - WebGPU's preferred canvas format belongs to the claimed OS
webgpu-canvas-format-vs-osnavigator.gpu.getPreferredCanvasFormat() returns the texture format the platform's compositor wants to be handed, and Chrome on Windows and… - A WebGPU device accepts every limit and feature its adapter advertises
webgpu-device-honours-adapterA WebGPU adapter advertises limits and features, and the device it creates is validated against them by Dawn, Chrome's WebGPU…
Clearcote is a browser built for fingerprint coherence
It is a Chromium fork, maintained by the same people who wrote this reference. It ships as a compiled browser rather than as a stealth script injected into someone else's — which is a description of how it is built, and is not an argument about how it behaves on this check.
This audit takes no position on how Clearcote scores on Render & GPU checks, on this one, or anywhere else. It has no baseline corpus of other people's fingerprints to rank you against and no vendor scoreboard — nearly every check is self-referential, asking one browser the same question through two independent APIs and reporting whether both answers can be true at once. It runs identically on any browser, including ours. Run it on yours and read the result yourself.
See the other checks in Render & GPU — the family webgl-state-reads-back belongs to.