input transformations

Allen Akin akin at
Mon Feb 5 16:36:18 PST 2007

(There were problems posting this first time around -- apologies to
those of you who receive a duplicate.)

On Mon, Feb 05, 2007 at 10:51:59AM -0500, David Reveman wrote:
| Why do we need a quad mesh to represent projective transforms? ...

I don't think you do; I believe it's sufficient to use four-coordinate
vertices with the homogeneous coordinates chosen correctly.  That's one
of the reasons the Vertex4 commands and formats exist.

|                                                              ... But I
| though that most OpenGL implementations were decomposing all GL
| primitives to triangles anyhow and it seemed most useful to have the
| input match the output. ...

I agree.

OpenGL doesn't specify the decomposition because there's no method
that's correct for all applications.  IrisGL tried a few different
techniques; none of them were universally acceptable.


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