Ambient Occlusion--bake into diffuse or lightmap
i am still relatively new to lighting in UDK and have questions.
I am just wondering on mobile udk apps, if I should bake ambient occlusion in with my diffuse maps. Or is AO something that can be baked into a lightmap?
Does a lightmap purely hold lighting information or does it also contain in AO--such as RGB = light. A = AO?
You can bake AO into your texture maps, to add some depth. Many artists do this anyways when creating stuff. They'll manipulate it in photoshop to make the diffuse map look a bit more realistic. In UDK there's AO rendering, which is more to improve shadows between objects. Mobile UDK doesn't have that feature though.
Lightmass does not render AO, it simply bounces the light around which makes for more realistic lighting. In an image that is RGBA, the A is for Alpha, or a mask that you can use on a material. Which you would use for something like hair where the RGB channels have the color of the hair and the Alpha channel cuts out the hair from the texture as a mask.
Ambient Occlusion doesn’t depend on light sources and therefore it’s not rendered/stored with lightmaps. SSAO is cheap but realtime version of AO.
If light mass is used to calculated the light maps (dunno about mobile as I've never used it) you can actually use it to calculate AO as well (it's in the world properties light mass settings). But previous to baking light (read UE3 normal) most artists would bake AO into the diffuse to help give the item depth and still would advise it if you are transferring complex details to low poly via hp-lp baking (normal / AO baking).