hello all- i just recently picked up a copy of andre's tricks od the 3d game programming gurus; execellent book, and i highly recommend it to all of you +1. my question is this - andre has a pretty simple algo that does Back Face Removal in world space; he calculates a polygon's normal and checks the dot product between that normal and a sight vector (cam-polygonpnt[0]). (see scenario 1, red lines are visible polygons) this technique seems to work well with his engine, but when i tried implementing it into mine, failure occured. the sight vector (cam-vertex) does not take into account camera rotations, so even if i rotate my camera 180 degrees, it'll all look the same to the hsr function, considering all of this is happening in world space. (See scenario 2) Right now, to take a single polygon from world->camera coordinates, it takes my engine 27 multiplications and a hoard of additions. if i add HSR after i have camera coordinates, it works perfectly, but the only speed ill get is from not having to rasterize the polygon, and right now im at a place where my rasterizer is fast enough that i dont care about drawing a few more hundred polys or so. but if i can get HSR working *BEFORE* the world->camera transformation, i can save [(27multiplications+27additions) <--- world->camera and (6multiplications+6subtractions) <--- camera->screen] PER polygon, which would boost my engine speed ~20-40 percent if im rendering a dense object (such as a bull, or human, or any convex object in the universe) thats roughly 50% invisible from any given point of view. Is there a way to do hsr before world->camera that doesnt reqire too many calculations and corrects my problem, or am i just doing something wrong? Help! btw, this is a ss of xGL, my 3d engine for PocketPC devices! this is a computer executable (so that i can take the screenshots) and it actually runs about 8x slower on the actual device (~52fps). not bad considering if you had just a loop that did nothing except flop back->front image buffer, you'd never hit more than 55fps [edited by - Uthman on August 12, 2003 7:10:39 AM]