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Rajveer
03-26-2002, 09:16 AM
Is there any way to draw a square plane by just specifying its coefficients from the plane equation: Ax + By + Cz + D = 0
as opposed to using glBegin(GL_QUADS) and specifying four sets of coordinates to construct the square plane.

DFrey
03-26-2002, 09:52 AM
No, because the plane equation defines a plane of infinite extent, and OpenGL would have no idea what extents you really want it to have, nor what side should be the front.

john
03-26-2002, 03:24 PM
Howdy,

well, there is no ~technical~ reason why opengl couldn't draw a plane from its coefficients; it just doens't, that's all.

1. drawing infinite planes could be clipped by the plane at infinity and the view frustum; and
2. a plane orientation can be found by the normal on the positive subspace of the plane

there are probably good reasons why opengl doesn't draw planes (such as that they are not entirely useful;-), but being infinite isn't a problem (points are technically infinitely small, for instance) and not knowing their orientation ~shouldn't~ be valid reasons. IMHO.

cheers,
John

DFrey
03-26-2002, 05:14 PM
You'll notice the original question did not say anything about infinite planes, and implied finite planes, that's why I mentioned the infinite extent. Because if you did not want the plane to have infinite extent, there is simply not enough information in the plane equation to indicate this. And yes, I am quite aware of being able to define a orientation based upon a sign convention (I know Quake did this), but I fear that would cause more confusion than its worth, unless you are comfortable thinking in terms of infinite oriented contours.