HTML5 game turns black? Check WebGL context recovery

In brief

• Confirm context loss before treating a black canvas as a graphics-recovery problem.
• Separate rebuilding the display from restarting the player's game session.
• Test the recovery path deliberately, including what happens when recovery does not complete.

This guide is for a game using a WebGL renderer. It is not a universal fix for every blank page, missing image or JavaScript error. If you bought a game source package, use these checks to give its developer a reproducible problem instead of only a screenshot.

First, record the actual failure

The webglcontextlost event signals that the browser detected a lost WebGL drawing buffer. Add diagnostic logging on the game's canvas before reproducing the problem, following MDN's event reference. Record the browser, device, build version and actions immediately before the failure.

If your logging captures no loss event, keep investigating loading errors, the console and the rendering code rather than declaring context loss proven. Compare the same build on a second device and preserve the original failure report. Avoid changing several renderer settings at once; that makes the result harder to interpret.

Make recovery explicit

For a restorable WebGL context, the loss handler must call event.preventDefault(). The Khronos extension specification source explains that restoration fails when the loss event has not been cancelled.

Recommended application flow: pause rendering, stop accepting actions that depend on the unavailable display, and show a clear recovery message outside the canvas. Keep the player's current state separate from graphics setup. Do not use a renderer restart as a reason to send another spin request; follow your project's documented session-recovery process.

If an engine manages your renderer, first inspect its recovery hooks and the version shipped with the source. Ask the developer to connect the application's pause and resume behaviour there, rather than adding a second competing recovery system.

Rebuild resources before resuming

Textures and buffers created before the loss are invalid after restoration. WebGL application state must be reinitialized and its resources recreated. MDN's restoration reference documents both requirements.

Treat rebuilding the scene as a distinct step. Check backgrounds, symbols, text and effects before enabling gameplay again. Include a bounded recovery policy with a useful retry or reload option if the scene cannot be rebuilt; do not leave the user looking at an endless spinner.

Test a controlled loss in a development build

The WEBGL_lose_context extension provides functions to simulate loss and restoration. Obtain the extension through WebGLRenderingContext.getExtension(). MDN documents the extension. Check that the returned extension object exists before using its methods.

Trigger a simulated loss, let the loss handler finish, then request restoration from a separate test action. After simulated restoration is requested, wait for webglcontextrestored before using the recovered context. The Khronos specification makes this asynchronous timing explicit.

Repeat during initial loading, an animation and an idle screen. For each test, record whether the scene returns correctly, controls resume once, and the round state remains consistent. These are suggested acceptance tests, not results measured on your game. Pair them with the mobile HTML5 performance checklist before release.