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Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →To save a WebGL render from an application you control, export its canvas with toBlob() or toDataURL() while the desired frame is still available. The default WebGL drawing buffer may be cleared after the browser composites it, so capture timing matters. If you need a later read, you can create the context with preserveDrawingBuffer: true, but that may reduce performance. If you cannot change the app, use a browser-level screenshot workflow instead.
Choose the capture method that matches your goal
| What you need | Use | Main trade-off |
|---|---|---|
| Only the rendered WebGL image, with access to the app code | Export the WebGL canvas with toBlob() or toDataURL() when the frame is readable. |
The default drawing-buffer contents may not remain available after compositing. |
| A canvas export later than the render call | Create the context with preserveDrawingBuffer: true, or design capture around a synchronous read or framebuffer. |
Preservation can cause significant performance loss on some platforms, and the context option must be set at creation. |
| The visible browser tab, including the page as rendered by the browser | Use a browser screenshot or an extension capture API. | This captures the visible view, rather than exporting only the canvas pixels. |
| A DOM-based image of a page section | Use a library such as html2canvas and export its resulting canvas. | It reconstructs an image from DOM and style information; it is not a native browser screenshot and may not reproduce WebGL output accurately. |
Export the WebGL canvas from your application
A WebGL canvas is an HTML canvas, so the standard canvas export methods can save its rendered content when the drawing-buffer pixels are available. The Khronos specification describes toDataURL() and readPixels() as ways to read drawing-buffer content. See the WebGL Specification for the buffer and alpha behavior.
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Export a PNG with toBlob()
Call the export at the point in your render flow when the intended frame is still readable. For example, call it after drawing the frame, not in an unrelated later task:
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const canvas = document.querySelector("canvas");
function saveCurrentFrame() {
canvas.toBlob((blob) => {
if (!blob) {
console.error("Canvas export failed");
return;
}
const link = document.createElement("a");
link.href = URL.createObjectURL(blob);
link.download = "webgl-shot.png";
link.click();
URL.revokeObjectURL(link.href);
}, "image/png");
}
// Call saveCurrentFrame() immediately after rendering the frame to capture.toBlob() is asynchronous, so a fragile drawing-buffer timing window can matter: starting the call at the correct point is safer than waiting and then initiating the export. If you require more control over pixel reads, the WebGL specification also describes readPixels(); account for the buffer dimensions, pixel format, and the coordinate orientation expected by your output code.
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Export as a data URL
For a small image or a workflow that needs an inline string, use toDataURL() while the desired frame is available:
const canvas = document.querySelector("canvas");
const dataUrl = canvas.toDataURL("image/png");
const link = document.createElement("a");
link.href = dataUrl;
link.download = "webgl-shot.png";
link.click();For larger images, a Blob avoids building a large base64 string in memory. Both methods depend on the canvas contents being readable when the export occurs.
Handle drawing-buffer clearing and capture timing
WebGL does not guarantee that the default drawing buffer retains its contents after the browser has composited the frame. With preserveDrawingBuffer false, later use of the context as an image source can have undefined behavior. A blank or stale export is often a timing problem, not evidence that the WebGL scene failed to render.
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Capture during the render flow
First try initiating the canvas export immediately after the code draws the frame you want. This avoids relying on the buffer remaining intact through a later browser task or compositing cycle. If the application uses a render loop, trigger capture from that loop at the correct point rather than from an unrelated timeout.
Preserve the drawing buffer only when needed
If capture must happen after the render call, request preservation when creating the context:
const canvas = document.querySelector("canvas");
const gl = canvas.getContext("webgl", {
preserveDrawingBuffer: true
});
if (!gl) {
throw new Error("WebGL is not available");
}This setting preserves the buffer until the application clears or overwrites it. It cannot be switched on after the context has already been created; Chrome’s developer guidance notes that context attributes cannot be changed after the first getContext() call. The Khronos specification warns that preservation can cause significant performance loss on some platforms, so prefer capture-time coordination or another readback design when practical.
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Capture a browser-rendered view when you cannot change the app
If you do not control the WebGL code, you generally cannot choose when it reads or exports its drawing buffer. A browser-level screenshot captures the rendered visible tab instead. The html2canvas FAQ points to chrome.tabs.captureVisibleTab() for Chrome, Edge, and Opera extension workflows, and suggests Puppeteer or Playwright for server-side screenshots driven by a real browser. Check the current documentation for the browser and tool you use; their APIs and options can vary.
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When a DOM reconstruction library is appropriate
html2canvas can create a canvas from page content and then export it. Its examples document export with toDataURL(), along with crop and scale options: html2canvas examples. This can suit a DOM-based page section, but it is not equivalent to capturing the browser’s actual rendered tab. The project’s documentation says its image is built from available DOM information and may not match the page’s real representation: html2canvas documentation.
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WebGL’s output is a browser-rendered canvas, so do not assume a DOM reconstruction will faithfully reproduce it. Cross-origin content and differences in browser rendering can also affect results. Use a browser screenshot for the visible rendered view or export the canvas directly when you own the app and need its pixels.
Account for alpha and output appearance
WebGL canvas export involves the context’s premultipliedAlpha behavior. The WebGL specification explains that toDataURL() may need to undo premultiplied color values when the requested image format does not specify premultiplied alpha, and that this operation is lossy. If exported edges or transparency look different from the browser view, check how the context and target image format handle alpha rather than assuming the screenshot is a raw copy of display pixels.
Troubleshoot blank, stale, or inaccurate captures
- The image is blank or shows an old frame: move the export closer to the draw call and verify it runs before the buffer is cleared or overwritten. If a later read is essential, create the context with
preserveDrawingBuffer: truebefore the firstgetContext()call. - Enabling preservation has no effect: context attributes are set when the context is first created. Recreate the canvas/context with the option from the start; it cannot be retrofitted onto an existing context.
- The captured page differs from the actual browser view: check whether you used a DOM reconstruction tool. html2canvas rebuilds output from DOM information rather than taking a native screenshot, and its result may not be pixel-accurate.
- Transparency or edge colors look different: inspect the WebGL context’s alpha behavior and the output format. Premultiplied-alpha conversion can be lossy.
- Content is missing in a DOM-based capture: investigate cross-origin resources and browser rendering differences, and prefer a browser-level screenshot when faithful visible output matters.
Or skip the browser setup
ScreenshotNeo takes a URL and returns an image or PDF, so it is useful when you need a browser-rendered page capture without managing a browser workflow. Its one-call request is:
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Frequently Asked Questions
Can I turn on preserveDrawingBuffer after creating a WebGL context?
No. Set it in the initial getContext() call; context attributes cannot be changed after context creation.
Does html2canvas take a real screenshot of a WebGL page?
No. It reconstructs an image from DOM and style information, which may not match the browser-rendered WebGL output.
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