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Re: [Public WebGL] Weird alpha issue.



> But the problem isn't alpha issues with images. It is issues with alpha
> in compositing with the HTML page which would probably also happen with
> vertex colors having alpha < 1.0.

I agree - this has nothing to do with alpha issues in textures or 2D
canvasses.  It's all to do with destination-alpha rendering contexts and
fragment shaders that write alpha<1.0...for whatever reason...not
necessarily from texture.

There are actually multiple problems that this test is currently
highlighting:

1) When you ask for a rendering context WITHOUT destination alpha - do you
actually get what you're asking for? (Not currently in Minefield - and the
last time I could test it, not in Chrome when it's using ANGLE under
Windows.  Chrome does seem to get this right for OpenGL rendering
contexts.)

2) Does the compositor correctly composite destination-alpha rendering
contexts into the HTML page?  (Currently, Minefield and Chrome disagree on
how this is done for partially transparent pixels - I don't know which of
them is correct - I suspect that whether a destination-alpha buffer
constitutes a pre-multiplied-alpha canvas is the bone of contention here).

3) When you write an alpha==0.0 pixel from your shader, will the pixel be
unconditionally culled (as both Chrome and Minefield do right now) - or
will the pixel's Z value be written to the depth buffer and a zero written
into the destination alpha plane (as the OpenGL ES 2.0 spec implies -
since it doesn't support glAlphaFunc)?

  -- Steve



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