Why Does UDK need Lightmaps & Unity doesnt?

CarlK3D

I've been using UDK for a little while now and I going through
Lightmaps at the moment

I understand that Building Lights in UDK Is Baking your lighting and shadows into the scene
And Lightmass calculates light bounce from objects

BUT I don't understand Why UDK needs a Lightmap (In my case a 2nd UV Channel in Maya) for each object and Unity Doesn't.

Any explanation between the 2 would be great

CarlK3D

*And when I say "Need" I mean it looks far better with a Lightmap on objects

Jacky

It basically needs a UV layout with no overlapping faces so you dont necessarily need a second UV channel if you can use the same layout for texturing as well. I don't know how Unity handles that though.

Brendan

In the Unity import options for a mesh you've probably got "Generate Lightmap UVs" ticked. If you make your own UV2 (lightmap) UVs you can untick this, but it does a decent job considering it's an auto-UV tool.

As for why one looks different to the other without lightmaps, I guess that's down to the shaders they use, probably. I heard something a while ago that UDK uses some shorthand lighting method by default that's supposed to work with lightmaps (could be why you say it needs lightmaps?).

CarlK3D

thanks for the responses Brendan and Jacky.
I didn't now Unity had a Generate Lightmap UVs but if what your saying is Both use lightmaps then I guess that answers my main question.

Another thing, I'm using a Dominant Directional Light as a Sun light and it casts the light & Shadows, However does the lightmap just bake the Lighting Information from the Dominant Directional Light onto the Lightmap UV? I think that's how it work just trying to make sure I completely understand

Obscura

udk can generate lightmap uvs too.you can do this, if you doubleclick to your mesh in the content browser, then click to mesh button, then generate unique uv's.you can switch between real time and precomputed lighting per object, if you hit f4 when your object is selected.in here, you can see the lighting channels under the lighting section, and you can switch with this, plus there is a checkerbox called use precomputed shadows.

CarlK3D

Yeah I looked into Generating Lightmap UV's in UDK but for more complex Objects it doesn't a good job, not to sure what precomputed lighting/shadows is though is it like Dynamic Lights? I want to bake all my Static Meshes to keep the engine running smooth.

Obscura

if you want only precomputed, check just static in the lighting channels an in the lighting options, and check use precomputed shadows.but then if there is an npc for example, it cant cast dynamic shadows to the surrounding objects.