WebGL - wait for texture to load

Question

How do I test if the WebGLTexture object is 'complete' ?

Currently I get this message: [WebGLRenderingContext]RENDER WARNING: texture bound to texture unit 0 is not renderable. It maybe non-power-of-2 and have incompatible texture filtering or is not 'texture complete'

I get this warning because the render-loop is trying to use the texture before its image has finished loading, so how to fix that?

Answer 1

The easiest way to fix that is to make a 1x1 texture at creation time.

var tex = gl.createTexture();
gl.bindTexture(gl.TEXTURE_2D, tex);
gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 1, 1, 0, gl.RGBA, gl.UNSIGNED_BYTE,
              new Uint8Array([255, 0, 0, 255])); // red

Then when the image loads you can replace the 1x1 pixel texture with the image. No flags needed and your scene will render with the color of your choice until the image has loaded.

var img = new Image();
img.src = "http://someplace/someimage.jpg";
img.onload = function() {
   gl.bindTexture(gl.TEXTURE_2D, tex);
   gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, img);

   // then either generate mips if the image uses power-of-2 dimensions or 
   // set the filtering correctly for non-power-of-2 images.
   setupTextureFilteringAndMips(img.width, img.height);
}

Just for the sake of saving people the trouble of running into the next problem they are most likely going to run into, WebGL requires mips or it requires filtering that doesn't require mips. On top of that it requires textures with dimensions that are a power of 2 (ie, 1, 2, 4, 8, ..., 256, 512, etc) to use mips. So, when loading an image you'll most likely want to setup the filtering to handle this correctly.

function isPowerOf2(value) {
  return (value & (value - 1)) == 0;
};

function setupTextureFilteringAndMips(width, height) {
  if (isPowerOf2(width) && isPowerOf2(height) {
    // the dimensions are power of 2 so generate mips and turn on 
    // tri-linear filtering.
    gl.generateMipmap(gl.TEXTURE_2D);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR_MIPMAP_LINEAR);
  } else {
    // at least one of the dimensions is not a power of 2 so set the filtering
    // so WebGL will render it.
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
  }
}

Answer 2

To fix that issue, use some boolean value to tell if the image has loaded.

var loaded = false,
    texture,
    img = new Image();

img.onload = function() {
    texture = gl.createTexture();
    // . . . 
    loaded = true;
};
img.src = "path/myimage.jpg";

// render-loop
function render() {
    if(loaded) {
        // use texture
    }
    else {
        // not loaded yet
    }
}