OpenGL – How to create Order Independent transparency?

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I am using something similar to that answer linked by @RetoKoradi comment but I got double layered transparent models with textures (glass with both inner and outer surface) with fully solid machinery and stuff around.

For such scenes I am using also multi pass approach and the Z-sorting is done by sequence of setting front face.

  1. render all solid objects

  2. render all transparent objects

    This is the tricky part first I set

    glGetIntegerv(GL_DEPTH_FUNC,&depth_funct);
glDepthFunc(GL_ALWAYS);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
glEnable(GL_CULL_FACE);

    I got the geometry layers stored separately (inner outer) so The Z-sorting is done like this:

    • Render outer layer back faces with glFrontFace(GL_CW);
    • Render inner layer back faces with glFrontFace(GL_CW);
    • Render inner layer front faces with glFrontFace(GL_CCW);
    • Render outer layer front faces with glFrontFace(GL_CCW);

    And lastly restore

    glDisable(GL_BLEND);
glDepthFunc(depth_funct);

  3. render all solid objects again

It is far from perfect but enough for my purposes it looks like this:

example

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