Search code examples
c#3dalphablendingslimdxalpha-transparency

Incorrect Geometry When Enabling Alpha Blending

I have a test application with enabled transparency achieved through alpha blending. The application is built in C# using SlimDX. However, on one of my objects that has alpha blending applied, I am getting a strange 'missing triangle' effect (see below).

enter image description here

The object is almost a cylinder.

I wondered if anyone more experienced in 3D computer graphics and/or the use of alpha blending might be able to point me in the right direction so I might understand this result - and hopefully remove it.

EDIT

I have tried to use an order independent blending shader and I get the same result. It would appear as though the pixels/fragments are being discarded due to failing the depth test. This does not make any sense to me.

Solution

  • You need to select a blending function that is order independent or try to sort you triangles along the view axis (which is impossible). See why here.

    EDIT:

    The problem is that the Z buffer prevents OpenGL from drawing pixels that are behind things that have already been drawn. Generally, that's pretty convenient, but when the thing in front is translucent, you need to see the things that are behind it.

    To get a correct looking geometry:

    • Put your depth buffer to read only mode.
    • Select an order independent blending function.