readPixels writes only the pixels it was asked to read
Every destination byte for a pixel outside the framebuffer keeps the value the page wrote there, and the pixels inside read back the cleared colour. N/A on Brave (severity: warn).
What a detector infers
readPixels writes into an array the page supplies, and the WebGL specification is precise about the edges: when the requested rectangle extends beyond the framebuffer, the destination bytes for the pixels outside it are left untouched. The probe fills a destination array with a sentinel value, then asks for a 16×16 block starting at (-4, -4) from an 8×8 framebuffer, so most of the requested area lies outside it.
A faithful implementation writes the 64 real pixels — each exactly the colour the framebuffer was cleared to — and leaves every sentinel byte beyond them alone. A noise pass that walks the whole destination array, the simplest way to perturb readPixels, overwrites bytes the browser never wrote. Measured on every stock browser tested: no sentinel byte changed. Only that side is measured: none of the spoofs tested here hooks readPixels, so no failing arm exists yet.
It is scored at warn anyway, because the expected answer is fixed by the specification rather than estimated from a population, and no ordinary configuration is known to change it. Brave perturbs WebGL readback as a stock privacy feature and is N/A.
How to resolve it
Leave readPixels to the implementation. Anything that post-processes the whole output array writes bytes the specification says stay untouched.
Nearby checks in Render & GPU
- A Direct3D renderer only appears under a Windows claim
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… - WebGL state reads back what the page just set
webgl-state-reads-backSome WebGL parameters are not capabilities but state the page itself controls. - 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… - WebGL renderer (software vs hardware)
webgl-not-softwareThe audit reads UNMASKED_RENDERER through the WEBGL_debug_renderer_info extension and matches it against SwiftShader, llvmpipe and Software.
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-readpixels-sentinel belongs to.