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Texturing Indexed Primitives

Started by SpreeTree Aug 9, 2003 at 7:04 AM 6 replies 350+ views

Original Post

Aug 9, 2003 at 7:04 AM

Hi Im rendering a simple cube using DrawIndexedPrimitive(...) and have encountered a little problem. Obviously I only define 8 verts for the primitive, but what happens if I want the 36 indices to have seperate texture coordinates. This is needed, i think, if I want each face to have the same texture. I was hoping there was something like SetTextureStream(...) or seomthing, but there doesnt seem to be. Any ideas?

JuNC

Aug 9, 2003 at 7:31 AM

No, if two vertices have different texture coordinates you need to duplicate the vertices for each texture coord.

[edited by - JuNC on August 9, 2003 8:31:47 AM]

SpreeTree

Aug 9, 2003 at 7:53 AM

Cheers, thought so, so thats what Ive done. That sucks a little, but what can you do about it

GekkoCube

Aug 9, 2003 at 10:29 AM

In cases where you must duplicate vertices (such as this due to texture coordinates)...would using DrawIndexPrimitives (index buffers) help over using DrawPrimitives (vertex buffers)?

Muhammad Haggag

Aug 9, 2003 at 10:52 AM

Keep in mind that a cube is a very extreme case. Generally, index buffers will save you bandwidth (being smaller in size and preventing duplication)

Peace,
Muhammad Haggag

[edited by - Coder on August 9, 2003 11:58:40 AM]

GekkoCube

Aug 9, 2003 at 11:00 AM

but what is the benefit?
i can only see memory usage being the benefit, whihc would probably improve the overall performance since you''re sending less vertices.

but other than that....

Namethatnobodyelsetook

Aug 9, 2003 at 11:20 AM

Saving memory isn''t enough?

Ok, how about by saving RAM you save GPU and AGP bandwidth, which is usually the first resource you''ll run out of.

Also, if two vertices share an index, the vertex may be transformed only once because it is in the post T&L cache. Using indices is the only way the card knows that the vertices are actually the same.

Toni Petrina

Aug 9, 2003 at 3:38 PM

Or you could simply create new texture composed of those smaller textures.

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