I have been working out some things using Texture Paint in 2.5. At the end of this in a few days I will be delivering a written tutorial to a magazine. I just want to make sure I have not missed anything.
Many of these things may also be true in 2.49 but here is what I have observed so far based on 2.5 tutorials and 2.49 documentation:
EDIT MODE AND UV:
Here in Edit Mode, when you have a UV map selected in the Texture Mesh panel, you load an image into the Image UV editor and that is the current UV Map and Image you are painting to in Texture Paint Mode. It seems as if you have to change this relationship in Edit Mode only.
TEXTURE PAINTING TO UV
Seems like this is a completely separate channel than mapping to the object Material Surface. Even though it will show up in the viewport as you paint on the model when in Texture Face or Multitexture display mode with Textured selected in the 3D view or Textured Solid checked in the Display panel.
In essence, you are only painting to the image that is being mapped to the current UV. The 3D view is both the input and feedback for this process.
While doing this you can paint with any textures you have set up in the Texture panel. And those textures do not need to be mapped to the material. They are simply used as brushes.
MAPPING TO THE MATERIAL
In the texture panel you can then map the image you are painting on to the various texture channels. The result of this - that is able to be displayed - is visible only if you turn use GSL Shading Display Mode.
So in essence you can be painting an image using textures and map that image at the same time to the Material.
RGB TO INTENSITY
I did quite a bit of experimenting with Alpha settings for Photoshop type layering. The Blending modes are useful.
But also I have found that painting shades of gray on a black background and checking RGB to Intensity allows you to map multiple layers but keep the Blend mode to MIX. What you do is control the color of the paint by changing the color here. Black remains alpha and shades to white are the color you set here. This is the same as painting on a transparent layer in Gimp or Photoshop. It allows you stack your layers and gives you the added flexibility to change the colors after you are done painting so you can tweak and have more control of the overall paint process after you are finished painting.
So you can layer multiple passes, skin texture, wrinkles, freckles and so on but also have full control to change the color of each after the fact. You could also paint tattoos. Use images as decals and so on. Also if you paint with a procedural, the layer can have a texture to it that you can not change later but you can manipulate the color after the fact.
This will be the focus of my tutorial. There are many things you can do with texture paint and other modes to work with. But I found this particular thing a useful feature to focus on. The tutorial will not be on all the things you can do with texture paint. Just this particular idea.
Regarding this, please let me know if I have missed anything obvious. There is more detail I will include in the tutorial but I just want to be open to any tips or features anyone else has encountered and of course any obvious flaws to my work flow I may have missed.
Thanks