
Example:

Modify the texture image. (I wrote "GIMP" on the texture)

Then click on the "Update" button and view the result:

To paint on the 3D window use the "Open 3D Paint Window" button, then you get a new image:

I used the IWarp plugin to make him smile.

Then I clicked on "Calculate Texture" and Texture Paint updated the texture image

To install Texture Paint, you need the Gtk+ library, an implementation of OpenGL (Mesa) and the GtkGLArea widget and the GIMP.
I have installed gimp-1.0.0, gtk+-1.0.5, Mesa-3.0 and gtkglarea-1.0.
Texture Paint is based on GiMd2Viewer-0.1, a Quake II model viewer by Lionel Ulmer.
The dialog windows of Texture Paint are created with Glade, a very good
dialog editor for GTK+. (You don't need to install Glade to use Texture
Paint)