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Ray Tracing problem, probably obvious :)

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Right, i'll get straight to the point :) basically i've to make a 3d game using C++ and OpenGL. my camera is just a basic 1st person camera and i've got a cube for a room. i've got a flat door on one of the walls, and i want my cross hair to change to a "open door" symbol when the camera forward vector intesects with any point on the door and i'm in range of the door, for now assuming the range is 1 for simplicity. i've got the ray tracing formula to be: x1 + x2*t = x3 + x4*u + x5*v y1 + y2*t = y3 + y4*u + y5*v z1 + z2*t = z3 + z4*u + z5*v with the left side of the equations being the camera position + the forward vector multiplied by t, and the right side of the equation being the object bottom left when u and v are 0, and the object top right when v and u are 1. i need to find t(as its the the "range" check, want to question if its below 1) and the only way i can see to do this is to simply perform the check over and over with u and v increased in small incriments between 0 and 1, however this would mean a rediculious amount of checks required specially given i wont only be having one door in the game lol. basically i've used this forum quite a few times before and found the answers i needed without having to post, but i cant find anything to help me here(unless i'm just being incompitant). i'm hoping someone can point out something obvious i'm missing or, possibly a more logical way of doing this :) Edit: btw, the problem here is the ray tracing, the cross hair thing, thats just to give context of what i'm doing. Thank you in advance, AzCopey [Edited by - AzCopey on March 17, 2008 6:04:24 PM]

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