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Debugging webgl

From: andrew cooke <andrew@...>

Date: Sun, 4 Mar 2012 19:14:18 -0300

Here are two ways to debug webgl, taken from
http://www.khronos.org/webgl/wiki/Debugging (but adding more detail).

First, which turned out not to be useful in my case, I tried adding
webgl-debug.js.  If you're using require.js (see my other examples here) then
you need to place webgl-debug.js in the "lib" directory and add a dependency

    function (a, u) {

      // code here


where the code will include something like:

      var gl = canvas.getContext('webgl');
      if (!gl) gl = canvas.getContext('experimental-webgl');
      if (debug) gl = WebGLDebugUtils.makeDebugContext(gl);

which wraps the context appropriately.  However, I had no errors (note that if
the wrapped context is undefined then you do get missing method errors).

Second, and more useful, I installed the WebGL inspector in chrome from

Once installed it seems that you need to load the web page and related scripts
via an http URL.  To do that, run

  python -m SimpleHTTPServer

in your development root and then change the file:// URLs to http://.

Loading the page, click the GL icon in the address bar to enable the extension
and then the green UI to display the interface.

Next, I needed to delay the draw method:

  setTimeout(draw, 5000);

so that I could reload the page and select *both* the red "Capture" and the
program in the "Programs" list before things ran.  After doing that, I saw
useful results.

And I now have two red triangles on a blue background.  The rest is details...


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