`react-doctor/webgl-no-sync-readback-in-animation-loop`

Synchronous GPU readback inside animation loop

Category: Performance
Severity: warn
Source: oxlint-plugin-react-doctor
Framework: global
Enabled when: always
Tags: webgl
Default: Enabled

Validate the diagnostic

Confirm the reported code matches this rule before you edit it.

Confirm the reported code matches react-doctor/webgl-no-sync-readback-in-animation-loop. Compare it with the Before example and verify the same API, framework, and execution context. Treat it as a false positive only when one of those conditions differs.

Compare the code

The corrected pattern shows a focused way to address the diagnostic.

Reported pattern

const gl = canvas.getContext("webgl2");
const pixel = new Uint8Array(4);
const animate = () => {
  gl.readPixels(0, 0, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixel);
  requestAnimationFrame(animate);
};

Corrected pattern

const gl = canvas.getContext("webgl2");
const pixel = new Uint8Array(4);
const animate = () => {
  requestAnimationFrame(animate);
};
const samplePixel = () => {
  gl.readPixels(0, 0, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixel);
};
canvas.addEventListener("click", samplePixel);

How to fix

Use the corrected pattern as a reference. Preserve behavior that the rule does not require you to change.

Copyable fix prompt

Copy this self-contained prompt into your coding agent after you confirm the diagnostic.

Fix every confirmed react-doctor/webgl-no-sync-readback-in-animation-loop diagnostic in the current repository. Required change: - Move GPU readback to a discrete or asynchronous path and reuse the latest completed result during frames.

Reference transformation:Before:

const gl = canvas.getContext("webgl2");
const pixel = new Uint8Array(4);
const animate = () => {
  gl.readPixels(0, 0, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixel);
  requestAnimationFrame(animate);
};

After:

const gl = canvas.getContext("webgl2");
const pixel = new Uint8Array(4);
const animate = () => {
  requestAnimationFrame(animate);
};
const samplePixel = () => {
  gl.readPixels(0, 0, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixel);
};
canvas.addEventListener("click", samplePixel);

Constraints: - Confirm the reported code matches the Before pattern. - Make the smallest change that fixes the root cause. - Preserve behavior and interfaces unrelated to this diagnostic. - Reuse existing project components, utilities, and conventions. - Do not introduce render-phase side effects, render-phase state updates, or Hooks rule violations. - Preserve resource ownership and cleanup. Do not move work into a hotter render or frame path. - Adapt identifiers and framework details instead of copying blindly. - Do not disable the rule or suppress matching code. Verification: - Run focused tests for the changed behavior. - Run React Doctor and confirm this diagnostic no longer appears. - Report the files changed and any checks you could not run.

More Performance rules from the rules reference:

react-doctor/zustand-no-fresh-selector-result: Zustand selector returns a fresh value
react-doctor/advanced-event-handler-refs: Store the handler in a ref and have the listener read `handlerRef.current()` — the subscription stays put while the latest handler is always called
react-doctor/async-await-in-loop: Collect the items and use `await Promise.all(items.map(...))` to run independent operations concurrently
react-doctor/async-defer-await: Move the `await` after the synchronous early-return guard so the skip path stays fast
react-doctor/async-parallel: Use `const [a, b] = await Promise.all([fetchA(), fetchB()])` to run independent operations concurrently

react-doctor/webgl-no-sync-readback-in-animation-loop