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I am facing a few problems with texturing this wine glas. What you see here is a render output from blender.I use ray transparency with a fresnel value of 5. I think, this is very close to what i would expect from a wine glas to look alike. Now i want to bake a texture for this glas. I know that i can not create an exact look alike. But i expect to be able to create something very transparent with some highlights on top of it.

In order to get the highlights i use a node based material

and my very first bake ends up like you can see in the picture on the right. This is how it looks in texture mode and that does not look too far away from the expected results. The fact that the glas looks tinted in blue is because due to its transparency we can see the blue sky behind the glas, but the rest of the scene is rendered in gray, so it just appears as if the glas where blue, but in reality it is almost transparent.
Now lets take a closer look at the texture itself. The texture is of size 512*512. It has been rendered with 2 additional levels of subdivision to get smoother results. I also have enabled oversampling. All faces on the object are also set to smooth. So i also expect to see a very smooth texture. But no, quite a few issues apparently spring up:

  1. what are these triangles at the top and bottom of the texture ? I do not expect to see this.
  2. There are a few black horizontal lines in the texture. I did not expect so many of them.
  3. The horizontal lines look somewhat blocky and rendered with less resolution.

Let us first take the whole sculptie to OpenSim (or a similar online world) and look, how it looks alike:

It is almost invisible except for some outlines at the top and at the bottom plus a few dark spots. That is not yet a good result. The major problem we face here is that the material lacks some physical properties like refraction. Hence the scene “behind” the glass should get a bit distorted due to the fact that light gets bended when passing through glass. But this effect is not implemented in the 3D environment. So the glass seems to disappear. Lets look at the bottom of the glas and zoom in a bit:

At the top center we see the transition of the shaft into the lower part of the glas. It is rendered in black and it looks very blocky. This is a close up of the top, the transition from shaft to bottom, bottom and bottom pole:

Let us now turn again to the texture. First i can now map the horizontal lines (black areas) to:

  1. The inner pole inside the glass (top row of triangles in the texture)
  2. the top of the glas.
  3. the transition from the upper part into the shaft.
  4. the transition from the shaft into the bottom.
  5. the bottom outline.
  6. The bottom pole (bottom row triangles in the texture)

The top and bottom problems are quickly to be explained. They come from the fact that at the poles the mesh is not made of quads, but of triangles. But we have modelled with quads all the time. So due to how the texture is created only half of each quad at the poles gets rendered. The other half of the quad is just folded into an edge. In principle the black triangles can be ignored, but in practice we still see dark areas bleeding into the visible area. So it is best to get rid of these artefacts. I show you further below how that can be done.

In order to understand the 4 other dark lines we need to go to blender and take a closer look into how light is rendered at all. And here i get stuck at the moment. I first need to find out, why this all happens, before i can explain it and continue with this article.