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I am in GLSL mode and I have a material with transparency, my problem is that transparency is not displayed as it is in the final render of BI. Instead of a smooth result in transparency I get patches that are more transparent than other areas and I dont know why. This problem happens in texture and material mode.

This is an image that displays the problem

and this is the blend file

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Answering here as well for completeness sake.

The issue with occlusion is fixed in blender, but the issue with sections having more or less transparency is not

The cause is that faces of transparent objects in blender are drawn randomly. Due to depth culling, if a front face is rendered first, then all faces behind it will get culled. So randomly, some parts of the mesh will get the face closer to the view rendered first and have the most transparency, while other parts will get more than one face rendered and be more opaque.

To solve this we would need to render faces sorted from back to front, but to keep viewport performance fast in blender, we skip this currently.

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It appears to me like an artefact of the way the viewport is drawn. As you move around you can see sections darken and lighten, these sections match up with faces in the mesh occluded by the front most faces.

There would appear to be some inconsistency when calculating the transparency as it passes through each face.

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  • $\begingroup$ yes exactly, also its as if some areas act as refractions to transparency, so they delay the way transparency pass through them like a glass. It looks to me as well as something wrong with how GLSL renders transparency but I dont know if my card (GT 755M 1GB) is to blame here, MacOS or Blender. If I start the BGE things get even worse. $\endgroup$ – Kilon Feb 6 '15 at 16:49
  • $\begingroup$ I'm on FreeBSD with a GT520, so OS isn't specific. It is blender using GLSL to draw transparency, I think it is a blender bug, not sure if it is a known limitation or easy to change. $\endgroup$ – sambler Feb 6 '15 at 17:34

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