Re: 2D 3D projection question

[Dair G. <da...@re...>]

Keith Wiley wrote:

>Can I easily take a pixel coordinate and determine which 3D object is
>under that pixel, in other words which 3D object (or actual triangle
>or trimesh I suppose) is shallowest in the z-buffer at the pixel's
>location?

You want to use a pick object - see QuesaPick.h.

If you're just interested in a single point use a window point pick, if
you want to catch everything under a rectangle use a window rect.


>I know Open-GL has routines for this sort of thing.

Actually the routines in QD3D/Quesa are considerably more sophisticated:
in OpenGL you tend to have to restort to tricks like rendering your
scene through a 1x1 viewport with every object rendered in a unique
colour.

Under Quesa you can just submit to a picking loop, then read off your
results at the end (the third type of pick is a world ray pick, which
can be used for simple collision detection: i.e., shoot a ray out of the
front of some object, and see what it hits).


-dair
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