CODEWITHSUNDEEP
javascriptwebgl
user4959035
user4959035

Reputation:

How to obtain a WebGLProgram object from the already created WebGL context?

I wonder, how can I obtain any WebGL program instance (WebGLProgram) from any desired WebGL context?

To fetch the WebGL context is NOT a problem. You are searching the DOM of the current page for the canvas element using document.getElementsByTagName() or document.getElementById(), if you know the exact canvas id:

let canvas = document.getElementById( "canvasId" );
let context = canvas.getContext( "webgl" );

Here we fetch the current context as I suppose, but if I want to get some shader parameters or get certain value from already running vertex/fragment shader - I need to have a WebGL program, which is associated with the current WebGL rendering context.

But I can't find any method in WebGL API like context.getAttachedProgram() or context.getActiveProgram().

So what is the way get the active WebGL program which is used for the rendering process? Maybe, there is some special WebGL parameter?

Upvotes: 3

Views: 3766

Answers (2)

user128511
user128511

Reputation:

There is no way to get all the programs or any other resources from a WebGL context. If the context is already existing the best you can do is look at the current resources with things like gl.getParameter(gl.CURRENT_PROGRAM) etc..

What you can do instead is wrap the WebGL context

var allPrograms = [];

someContext.createProgram = (function(oldFunc) {
   return function() {
     // call the real createProgram
     var prg = oldFunc.apply(this, arguments);

     // if a program was created save it
     if (prg) {
       allPrograms.push(prg);
     }

     return prg;
   };
}(someContext.createProgram));

Of course you'd need to wrap gl.deleteProgram as well to remove things from the array of all programs.

someContext.deleteProgram = (function(oldFunc) {
   return function(prg) {
     // call the real deleteProgram
     oldFunc.apply(this, arguments);

     // remove the program from allPrograms
     var ndx = allPrograms.indexOf(prg);
     if (ndx >= 0) {
        allPrograms.splice(ndx, 1);
     }
   };
}(someContext.deleteProgram));

These are the techniques used by things like the WebGL Inspector and the WebGL Shader Editor Extension.

If you want to wrap all contexts you can use a similar technique to wrap getContext.

HTMLCanvasElement.prototype.getContext = (function(oldFunc) {
   return function(type) {
      var ctx = oldFunc.apply(this, arguments);
      if (ctx && (type === "webgl" || type === "experimental-webgl")) {
        ctx = wrapTheContext(ctx);
      }
      return ctx;
   };
}(HTMLCanvasElement.prototype.getContext));

Upvotes: 6

WacławJasper
WacławJasper

Reputation: 3364

gl.getParameter(gl.CURRENT_PROGRAM). Check out https://www.khronos.org/files/webgl/webgl-reference-card-1_0.pdf pg 2 to the right.

Upvotes: 6

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