[whatwg] Adding features needed for WebGL to ImageBitmap

[Gregg Tavares]

In order for ImageBitmap to be useful for WebGL we need more options

Specifically

premultipliedAlpha: true/false (default true)
Nearly all GL games use non-premultipiled alpha textures. So all those
games people want to port to WebGL will require non-premultipied textures.
Often in games the alpha might not even be used for alpha but rather for
glow maps or specular maps or the other kinds of data.

flipY: true/false (default false)
Nearly all 3D modeling apps expect the bottom left pixel to be the first
pixel in a texture so many 3D engines flip the textures on load. WebGL
provides this option but it takes time and memory to flip a large image
therefore it would be nice if that flip happened before the callback from
ImageBitmap

colorspaceConversion: true/false (default true)
Some browsers apply color space conversion to match monitor settings.
That's fine for images with color but WebGL apps often load heightmaps,
normalmaps, lightmaps, global illumination maps and many other kinds of
data through images. If the browser applies a colorspace conversion the
data is not longer suitable for it's intended purpose therefore many WebGL
apps turn off color conversions. As it is now, when an image is uploaded to
WebGL, if colorspace conversion is
off<http://www.khronos.org/registry/webgl/specs/latest/#PIXEL_STORAGE_PARAMETERS>,
WebGL has to synchronously re-decode the image. It would be nice if
ImageBitmap could handle this case so it can decode the image without
applying any colorspace manipulations.

If it was up to me I'd make createImageBitmap take on object with
properties so that new options can be added later as in

    createImageBitmap(src, callback, {
       premultipliedAlpha: false,
       colorspaceConversion: false,
       x: 123,
    });

But I'm not familiar if there is a common way to make APIs take a options
like this except for the XHR way which is to create a request, set
properties on the request, and finally execute the request.

thoughts?