a-b-street/abstreet · error · anyhow::Error

error getting context for WebGL 1.0

Error message

error getting context for WebGL 1.0: {:?}

What it means

webgl1_glow_context requests a "webgl" (WebGL 1.0) context from the canvas. If the get_context call itself errors (a JS-level failure, not a null return), the JsValue is wrapped in this anyhow error. It is the GL1 counterpart of error 216 and occurs during setup's fallback path.

Solutions

  1. Enable WebGL/hardware acceleration in the browser; verify about:gpu or browser diagnostics.
  2. Ensure no prior 2d/experimental context was requested on the same canvas.
  3. If neither WebGL 1 nor 2 works, the environment cannot run the renderer — switch browsers or run natively (non-wasm).
  4. In setup, surface both errors to the user with guidance to enable GPU acceleration.

Example fix

// before
let maybe_context: Option<_> = canvas
    .get_context("webgl")
    .map_err(|err| anyhow!("error getting context for WebGL 1.0: {:?}", err))?;
// after: caller-side clear diagnostics
let ctx = webgl1_glow_context(canvas)
    .map_err(|e| anyhow!("GPU rendering unavailable (enable WebGL/hardware acceleration): {}", e))?;
Defensive patterns

Strategy: try-catch

Validate before calling

// Detect any WebGL support before setup
if (!document.createElement('canvas').getContext('webgl')) {
  renderNoWebGLMessage(); // block app start early with guidance
}

Try / catch

// Catch and show actionable user guidance
let ctx = webgl1_glow_context(canvas).map_err(|e| {
    anyhow!("Enable GPU/WebGL in your browser settings. details: {}", e)
})?;

Prevention

When it happens

Trigger: setup() falls back to webgl1_glow_context (after WebGL 2 is unavailable) and canvas.get_context("webgl") rejects — tainted canvas, WebGL blocked entirely, or binding-level JS exception.

Common situations: Environments with all WebGL disabled (privacy hardening, headless servers, blocked GPU acceleration); canvas previously acquired with a different context type; browsers whose getContext throws under strict security policies.

Understand the failure class

Background: "unsupported platform" / "not supported on this platform" errors: what they mean and how to fix them — this error's family across 47 libraries.

Related errors

AI-assisted analysis of a-b-street/abstreet@0964f29315 (2026-09-13). Data as JSON: /api/errors/9061e1b71c916b6c. Report an issue: GitHub.

Appendix: source

Thrown at widgetry/src/backend_glow_wasm.rs:97

        })
        .unwrap();

    fn webgl2_glow_context(canvas: &web_sys::HtmlCanvasElement) -> Result<glow::Context> {
        let maybe_context: Option<_> = canvas
            .get_context("webgl2")
            .map_err(|err| anyhow!("error getting context for WebGL 2.0: {:?}", err))?;
        let js_webgl2_context =
            maybe_context.ok_or(anyhow!("Browser doesn't support WebGL 2.0"))?;
        let webgl2_context = js_webgl2_context
            .dyn_into::<web_sys::WebGl2RenderingContext>()
            .map_err(|err| anyhow!("unable to cast to WebGl2RenderingContext. error: {:?}", err))?;
        Ok(glow::Context::from_webgl2_context(webgl2_context))
    }

    fn webgl1_glow_context(canvas: &web_sys::HtmlCanvasElement) -> Result<glow::Context> {
        let maybe_context: Option<_> = canvas
            .get_context("webgl")
            .map_err(|err| anyhow!("error getting context for WebGL 1.0: {:?}", err))?;
        let js_webgl1_context =
            maybe_context.ok_or(anyhow!("Browser doesn't support WebGL 1.0"))?;
        let webgl1_context = js_webgl1_context
            .dyn_into::<web_sys::WebGlRenderingContext>()
            .map_err(|err| anyhow!("unable to cast to WebGlRenderingContext. error: {:?}", err))?;
        Ok(glow::Context::from_webgl1_context(webgl1_context))
    }

    (
        PrerenderInnards::new(gl, is_gl2, program, Some(WindowAdapter(winit_window))),
        event_loop,
    )
}

fn webgl2_program(gl: glow::Context) -> Result<(glow::Context, glow::Program)> {
    let program = unsafe {
        build_program(
            &gl,

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