There are two ways to rendermap multiple objects: you can simultaneously create a single set of rendermap images for each object or you can create a single set of rendermap images that is used by all of the objects. These techniques are described in this section.
If your scene contains several objects that you want to rendermap separately, the easiest and fastest thing to do is to generate their rendermaps all at once. Not only is it faster to set the rendermaps' options simultaneously, it is also considerably faster to generate rendermaps for several objects at once than one at a time.
Generating a single set of rendermap images for multiple objects is a bit more complex than generating several objects' rendermaps at the same time. The trick is to group the objects and give each object a set of UV coordinates used strictly for rendermapping. You can then adjust those sets of UV coordinates in such a way that they will not overlap when placed on the same texture image. When you generate the rendermap, the properly positioned UV coordinates are used to sample all of the objects and write their textures to the correct position on a single image.
The illustrations for this procedure are taken from a simple scene in which four spheres have been turned into eyes using a complex combination of procedural shaders. The rendermap image shown is a surface color map, though the method applies equally to any type of rendermap image.
Although the objects that you want to rendermap are textured already, apply a second texture projection to each of them. These are the projections that you'll use to generate the rendermap, so make sure not to use them to texture your objects.
From the UVs menu in the texture editor menu bar, select the texture projections that you created specifically for generating the rendermap. You can Shift+click the appropriate projection for each object to display them all simultaneously.
Transform each object's UV coordinates so that they occupy only a portion of the total texture image. Make sure that no object's UV coordinates spill into the space occupied by another object's UV coordinates.