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Re: Picking

On Wednesday, December 25, 2002, at 08:27 AM, Brian Greenstone wrote:

on 12/25/02 10:17 AM, Dario Accornero at email@hidden wrote:

I'm about to implement the same thing that Brian is doing, and, yes,
any sample code would definitely help...

Well, I've decided that there's just no way to do real picking in OpenGL, so
I'm currently writing my own picking functions to do ray->triangle
intersection tests.

What's wrong with the glReadPixels second pass?

My own hard-won experience on this (let's see, so far we've used GL_SELECT (too inaccurate), then glReadPixels (too convoluted a code path, inconsistent results on early 10.x), then ray casting (too slow for big data, incompatible with gpu-side procedural geometry & deformations), then a fancy cyclic-coord-descent + octree scheme (fast, but convoluted, and no gpu-side stuff), and finally back to glReadPixels)...

Use GL_SELECT for drag-selection. Nothing else will be as fast for area selection.
Use glReadPixels for picking. We had to do a significant restructuring of our render pipeline to make this work cleanly, but having done it, it works better and faster than anything else.

It took 2+ years to get right, but finally drag-selection, dragging, and picking all work perfectly, on all geometry, all the time, and are _fast_. Nightmare getting there. Save yourself the trial-and-error.

I'm on a plane at the moment, but I'll post some code later this week.

Dan
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 >Re: Picking (From: Brian Greenstone <email@hidden>)



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