Vertex programs and the raster position

I’m experiencing a rather bizarre problem with glRasterPos when using vertex programs on NV hardware.

I’m rendering a bunch of particles (I’m billboarding, so they’re actually textured quads). Basically what I’m doing is use glRasterPos to find the projected location of a particle in the viewport, reading the value of the pixel there, then rendering the quad over the top.

Problem seems is that GL_RASTER_POSITION_VALID never seems to be set to true, even for particles which do actually render something into the frame buffer.

Has anybody else had problems with this?

According to the spec. the coordinates supplied to glRasterPos should be fed through the vertex program just as if they we given to glVertex.

This is on older GeForce hardware, with 23.13 drivers, so the vertex programs are being emulated in software, but nevertheless I don’t think it should work like this!

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