Quote: --- Original message by: Mootjuh
Opening the shader_environment. Setting the shader type(which is just above the part where you can browse the diffuse and detail maps) to blended. The alpha map of the diffuse will determine where to add which detail map. If a bit is completely white it will use detail map 1 and if there's a black spot in the alpha that part will have detail map 2. Anything gray will be a mix between detail map 1 and 2.

Starting from Halo 3 shaders could use RGBA blend maps. This is a separate texture which has a detail mask, just like the alpha map in the diffuse used for CE shader_environments, in each channel. This gives one the ability to use like 4 or 5 detail maps in 1 shader.

You can't use all the detail mask in a RGBA blend map with a CE shader. Your best bet would be combining some and merge them.