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does the same static object in the scene have the same lightmap uv coordinate?

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for example , i put 3 instances of a static mesh in the level, should i use the same lightmap uv coordinate for them and  then pack the 3 square block into one lightmap atlas texture, or complete different lightmap  uv coordinate for each one so that  the atlas texture can be more compact, but the latter one also need more vertex memory because the lightmap uv coordinate can not be reused by different instances with the same mesh type

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I'm not sure what you actually mean ( your statements sound a bit contradictory to me ), but I'm afraid that you can not reuse anything along different instances of a mesh, when it comes to lighting them using a lightmap. They occupy different places and orientations in space, so they must be lit differently by the lights in the scene.

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i'm sorry for my descriptionsad.png  

here is my vertex format 


struct MeshVertex


float3 pos:POSITION


float2 tex_diffuse:TEX0

float2 tex_lightmap:TEX1  



every vertex of a mesh has two uv coordinates ,one for texture one for lightmap , now i have 2 solutions:

1. generate the lightmap uv of each mesh type by 3DMAX , during the lighting building  process i just pack 3 single lightmap into a big atlas texture ,so each instance just need a uv offset and  uv scale to the atlas texture to get its corresponding lightmap data area . 

2.  pack all instances into a single mesh  and generate a lightmap coordinate set for  that big mesh and then distribute the corresponding subset to each instance  after level design has been finished in the level , the uv space of lightmap can be more compact than the former one.An obvious drawback of it is the  extra vertex buffer needed for each instance and some extra vertex stream stat change during rending


which one is better?

Edited by jdyyx1984

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