Disable writing in depth buffer from glsl

Question

All geometry is storing in one VBO (Transparent + Not transparent). I can not sort geometry. How I can disable writing in depth buffer from glsl without loss the data colors?

Answer 1

If I understand right, you want to disable depth writes because you draw both opaque and transparent objects. Apart from the fact that it doesn't work that way from within GLSL, it would not produce what you want, if it did.

If you just disabled depth writes ad hoc, the opaque objects coming after a transparent object would overwrite it, regardless of the z order.

What you really want to do is this:

1. Enable depth writes and depth test
2. Draw all opaque geometry. If you can, in a roughly sorted (roughly is good enough!) order, closest objects first.
3. Disable depth writes, keep depth test enabled
4. Enable blending
5. Draw transparent objects, sorted in the opposite direction, that is farthest away first. This occludes transparent objects with opaque geometry and makes blending work correctly.

If, for some reason, you can't sort the opaque geometry (though there is really no reason why you can't do that?), never mind -- it will be slightly slower because it does not cull fragments, but it will produce the same image.

If, for some reason, you can't sort the transparent geometry, you will have to expect incorrect results where several transparent objects overlap. This may or may not be noticeable (especially if the order is "random", i.e. changes frame by frame, it will be very noticeable -- otherwise you might in fact get away with it although it's incorrect).

Note that as datenwolf has pointed out already, the fact that several objects are in one VBO does not mean you can't draw a subset of them, or several subsets in any order you want. After all, a VBO only holds some vertices, it is up to you which groups of them you draw in which order.

Answer 2

You can't.

I can not sort geometry.

Why? You think because it's all in one VBO? Then I've got good news: It's perfectly possible to draw from just a subset of a buffer object.