CompuServe Messages

Hi Judy, << Could someone explain to me what is Z-Buffering and what are its advantages? >> I've tried to find all of Gary's recent comments on the z-buffer. Here they are… "Yup. You can access the z-buffer now. There's a new IPAS API call (vpost_zbuf) that'll give you a 4-BYTE-per-pixel version of it (which would be 1.2Mb for a 640×480 screen, btw). We'll put a simple little IXP up here in DL1 after R4 ships that lets you save that to an image file if you want. – G In addition to Phil's excellent technique for making bump-maps, the z-buffer gives you a depth mask that you can use for compositing, so you can do your own atmosphere-like effects. David Stinnett has this method down cold, so if he's around, he could explain it for ya. – G I can understand your confusion, but it isn't you. There isn't supposed to be any antialiasing in a z-buffer. Consider this. In the z-buffer, a pixel can have any number of surfaces inside of it, but only the nearest surface's distance is recorded. How would antialiasing be possible? You could certainly have a finer-resolution z-buffer than 8-bits (since the z-buffer info is stored as a floating-point number), but you'd have to have an IXP that wrote it out in higher bit-depth (24, for example) and then an application that could use that extra info. – G Good point. What you really need for z-buffer compositing effects is an IXP that does some filtering around the objects. Here's what's actually going on in SEEZ. SEEZ takes the 'zmin' and 'zmax' values from the FrameParm structure, then normalizes the values between the z minimum and z maximum to range from 255-0. That's why SEEZ causes the nearest part of the objects in the scene to be bright white. If the code is altered with some arbitrary near/far values, the objects will get dimmer as they recede. (Tom wrote SEEZ this way so that he could mess around with random dot stereograms.) To summarize, each pixel's Z value reflects the distance from the camera to the nearest object fragment in that pixel. If the view is not a camera, then the Z value in the pixel is not the distance from the viewer (since the view is orthographic, there is no viewpoint) but the distance from the point being looked at. In orthographic views, Z values can be negative. True, this can cause aliasing to occur if simple compositing is done, and won't work well for transparent objects, but with some filtering, it can work very effectively. This is what the folks at Digimation are probably doing to get their depth-of-field zbuffer-based routine, and it's also why I put the source code to SEEZ in the zip file… so other developers could take the concepts and run with them (a la Digimation). – G" jonas[adesk]