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Stripe's .objf file format

Started by bishop_pass Jan 28, 2003 at 2:59 PM 3 replies 800+ views

Original Post

Jan 28, 2003 at 2:59 PM

Stripe. In the file format spec, (click on file format on their homepage) does anyone know why the ''t'' parameter would ever have more than 3 vertices, and why the ''q'' parameter would ever have more than 1 vertex? And sometimes, the ''t'' parameter only has 2 vertices. It seems like ''t'' would signify a new strip, and all of the following vertices in the file until a new ''t'' is found would simply be the list of vertices in the strip. If this is the case, what is the point in varying the number of vertices in the ''t'' and ''q'' lists?

bishop_pass

Jan 28, 2003 at 3:24 PM

I''m looking at the output, and it appears to just be meta-info, letting you know that vertices are being swapped. From the renderer''s point of view, I believe this info can be ignored if the renderer wants to ignore it, and just assume that the list of vertices beginning with ''t'' is a triangle strip list - paying no attention to whether vertices are being swapped or not.

bishop_pass

Jan 28, 2003 at 3:32 PM

Then again, I don''t know. What is the point in beginning the strip with 3 4 3, as they are doing in the second set?

paulc

Jan 30, 2003 at 7:28 AM

The only reason I can think of is that its doing some sort of degenerate tri stuff, but it isn''t obvious why. The file format doesn''t really seem to have much logic to it. Surely a tri-strip should start with 2 initial vertices and then each subsequent vertex forms a new tri, so a simple list of vertex indices would be enough:
t 6 2 4 9 3 5 7 8 (totally random example)
Why have the q''s when you a sequence of t''s as above will do?

GameCat

Jan 30, 2003 at 9:35 AM

I haven''t looked at the spec so this is just a guess, but it might signify the changing of winding order. On certain older sgi systems I think you could change the winding order of a strip even in the middle of submitting one. I think the API functionality for this was removed with OpenGL so it''s ancient as hell but it''s a guess.

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