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From: Jon Watte <hplus@mi...>  20030224 22:28:14

We use a force system, where the force applied in a direction is subdued by the amount of steepness, after some amount of "accepted" steepness. Thus, you can't walk up really steep slopes, but you also don't fall if you manage to jump to such a slope. Well, there are slopes that are steep enough that you fall because the physics doesn't find any ground to stand on, but there exists an intermediary degree of steepness. Cheers, / h+ Original Message From: gdalgorithmslistadmin@... [mailto:gdalgorithmslistadmin@...]On Behalf Of Igor Kravtchenko Sent: Monday, February 24, 2003 2:18 PM To: gdalgorithmslist@... Subject: [Algorithms] "nonclimbable" elements I would be interested to know whether you use special method or not to avoid the player (on foot) to climb on certain elements in a 3D environment. For example, a too high slope, a box, a too complex geometry, etc... Do you choose to suddently stop the player when a such elements is encountered or do you make it to fall ? Do you need to flag your polygon or everything is running automatically, etc... ? Igor. 
From: Igor Kravtchenko <igor@ob...>  20030224 22:19:02

I would be interested to know whether you use special method or not to = avoid the player (on foot) to climb on certain elements in a 3D environment. For example, a too high slope, = a box, a too complex geometry, etc... Do you choose to suddently stop the player when a such elements is = encountered or do you make it to fall ? Do you need to flag your polygon or everything is running automatically, = etc... ? Igor. 
From: Gribb, Gil <ggribb@ra...>  20030224 21:43:50

This just turns out to be just a linear problem with 6 unknowns. Lets call the two vectors we are looking for s and t. S will go in the u direction and t will go in the V direction. Here are the equations you need to solve. Given: N, the triangle normal P0, P1, P2, the 3 points of the triangle U0,U1,U2, V0,V1,V2, the texture coordinates of the three vertices s dot N = 0 // s is perpendicular to the polygon normal. t dot N = 0 // t is perpendicular to the polygon normal. s dot (P1P0) = U1  U0 // change in position dot s is proportial to change in U s dot (P2P0) = U2  U0 // change in position dot s is proportial to change in U t dot (P1P0) = V1  V0 // change in position dot t is proportial to change in V t dot (P2P0) = V2  V0 // change in position dot t is proportial to change in V 6 equations, 6 unknowns, solve it. I guess I skipped a step getting those last 4 equations, but you should at least be able to confirm that they are true. The easiest way to see this is that you can subtract P0 from all 3 coordinates and (U0,V0) from all three texture coordinates without changing the problem or solution. Gil Original Message From: Tom Vykruta [mailto:tom@...] Sent: Monday, February 24, 2003 1:32 PM To: 'gdalgorithmslist@...' Subject: [Algorithms] Generating texturespace binormal/tangent in object space for bumpmapping [bcc][fake adr] I am implementing the embossbumpmapping technique for our engine. For those not familiar with it, it basically involves a pervertex projection of the relative light vector into a perpolygon "texturespace" matrix. The texture space matrix is derived from the UV mapping. Depending on how the artist mapped the texture onto the polygon, you can generate a tangent and binormal vector which point in the direction of the "U"'s and the "V"'s. The NORMAL for this texturespace matrix is just the polygon's normal, since the texture's binormals ofcourse lie within the polygon's XZ plane. Another way to visualize the tangent and binormal is this: Plot the UV coordinates of your polygon's 3 vertices onto a texture map. The tangent will always point horizontally within the texture map (vector (1, 0)) , and the binormal will always point vertically (vec(0,1)). I've derived my own method of computing the tangent/binormal, unfortunately it is incomplete. It does not take into account a polygon that's skewed. I generate the two vectors by using only one edge, which is incorrect. At least two edges must be taken into account. For this reason I won't bother getting into details about my technique. Another algorithm exists that I found on several websites, which seems to be complete. Unfortunately in all cases either the authors themselves don't understands how it works, or don't bother explaining. If anyone is familiar with this algorithm please explain the math behind it. Follow the URL to see sample source code on how to generate the tangent and binormal given a polygon. I'm including a small excerpt from the webpage. I worked out the math on a whiteboard and it almost started to make sense but now I really need to impliment this thing and am out of research time :) I'm sure the code works, but I don't feel comfortable using it unless I understand the HOW and WHY. Thanks a million! http://tfpsly.planetd.net/english/3d/pplight_bump.html <http://tfpsly.planetd.net/english/3d/pplight_bump.html>; //X being the cross product For each face { (x,y,z) = (p2>xp1>x,p2>up1>u,p2>vp1>v) X (p3>xp1>x,p3>up1>u,p3>vp1>v) if (x!=0) { NORMALIZE(x,y,z) p1>Tx += y/x; p1>Bx += z/x; p2>Tx += y/x; p2>Bx += z/x; p3>Tx += y/x; p3>Bx += z/x; } ....see webpage for full algorithm... Tom Vykruta Surreal Software 
From: Jon Watte <hplus@mi...>  20030224 21:42:43

If you go through all that work, why don't you instead use the same matrix to project a normal, looked up in a normal map bump map (instead of emboss bump map), out to object space? Then you can dot with the light vector to get perpixel lighting, in addition to easily generate the proper perpixel reflection vectors for environment mapping (if you have enough dependent lookup stages). Anyway, the tangent basis needs to be orthonormal to avoid stretchandskew problems which will lead to unnormalized lighting which will lead to blotchy lighting. Generating the third vector by crossing two vectors which allegedly are already unit length and rightangle, is actually a perfectly fine thing to do. If you generate a matrix using U, V and normal and don't orthonormalize the matrix, you will get incorrect lighting results. Note, unless your artists are rightangle nonstretching texture map GODs (who can, additionally, warp the rules of Euclidean geometry) you will not be able to generate orthonormal basis matrices for every vertex. You have to make it not match up with at least one of the three "directions". The algorithm which you post, seems to have a singularity where the X coordinate of the two points is the same, which may be a significant problem for some geometry. The "real" way of getting the data would be to figure out which way, in model space, U, V and the normal "points"; slam those into the rows of your matrix, and then use your favourite matrix orthonormalization code. The code you post seems to be an algebraically simplified version of this algorithm, that only works for certain orientations, which doesn't feel robust to me. Cheers, / h+ Original Message From: gdalgorithmslistadmin@... [mailto:gdalgorithmslistadmin@...]On Behalf Of Tom Vykruta Sent: Monday, February 24, 2003 11:32 AM To: 'gdalgorithmslist@...' Subject: [Algorithms] Generating texturespace binormal/tangent in object space for bum pmapping I am implementing the embossbumpmapping technique for our engine. For those not familiar with it, it basically involves a pervertex projection of the relative light vector into a perpolygon "texturespace" matrix. The texture space matrix is derived from the UV mapping. Depending on how the artist mapped the texture onto the polygon, you can generate a tangent and binormal vector which point in the direction of the "U"'s and the "V"'s. The NORMAL for this texturespace matrix is just the polygon's normal, since the texture's binormals ofcourse lie within the polygon's XZ plane. Another way to visualize the tangent and binormal is this: Plot the UV coordinates of your polygon's 3 vertices onto a texture map. The tangent will always point horizontally within the texture map (vector (1, 0)) , and the binormal will always point vertically (vec(0,1)). I've derived my own method of computing the tangent/binormal, unfortunately it is incomplete. It does not take into account a polygon that's skewed. I generate the two vectors by using only one edge, which is incorrect. At least two edges must be taken into account. For this reason I won't bother getting into details about my technique. Another algorithm exists that I found on several websites, which seems to be complete. Unfortunately in all cases either the authors themselves don't understands how it works, or don't bother explaining. If anyone is familiar with this algorithm please explain the math behind it. Follow the URL to see sample source code on how to generate the tangent and binormal given a polygon. I'm including a small excerpt from the webpage. I worked out the math on a whiteboard and it almost started to make sense but now I really need to impliment this thing and am out of research time :) I'm sure the code works, but I don't feel comfortable using it unless I understand the HOW and WHY. Thanks a million! http://tfpsly.planetd.net/english/3d/pplight_bump.html //X being the cross product For each face { (x,y,z) = (p2>xp1>x,p2>up1>u,p2>vp1>v) X (p3>xp1>x,p3>up1>u,p3>vp1>v) if (x!=0) { NORMALIZE(x,y,z) p1>Tx += y/x; p1>Bx += z/x; p2>Tx += y/x; p2>Bx += z/x; p3>Tx += y/x; p3>Bx += z/x; } ....see webpage for full algorithm... Tom Vykruta Surreal Software 
From: Tom Vykruta <tom@su...>  20030224 21:17:53

I am implementing the embossbumpmapping technique for our engine. For those not familiar with it, it basically involves a pervertex projection of the relative light vector into a perpolygon "texturespace" matrix. The texture space matrix is derived from the UV mapping. Depending on how the artist mapped the texture onto the polygon, you can generate a tangent and binormal vector which point in the direction of the "U"'s and the "V"'s. The NORMAL for this texturespace matrix is just the polygon's normal, since the texture's binormals ofcourse lie within the polygon's XZ plane. Another way to visualize the tangent and binormal is this: Plot the UV coordinates of your polygon's 3 vertices onto a texture map. The tangent will always point horizontally within the texture map (vector (1, 0)) , and the binormal will always point vertically (vec(0,1)). I've derived my own method of computing the tangent/binormal, unfortunately it is incomplete. It does not take into account a polygon that's skewed. I generate the two vectors by using only one edge, which is incorrect. At least two edges must be taken into account. For this reason I won't bother getting into details about my technique. Another algorithm exists that I found on several websites, which seems to be complete. Unfortunately in all cases either the authors themselves don't understands how it works, or don't bother explaining. If anyone is familiar with this algorithm please explain the math behind it. Follow the URL to see sample source code on how to generate the tangent and binormal given a polygon. I'm including a small excerpt from the webpage. I worked out the math on a whiteboard and it almost started to make sense but now I really need to impliment this thing and am out of research time :) I'm sure the code works, but I don't feel comfortable using it unless I understand the HOW and WHY. Thanks a million! http://tfpsly.planetd.net/english/3d/pplight_bump.html <http://tfpsly.planetd.net/english/3d/pplight_bump.html>; //X being the cross product For each face { (x,y,z) = (p2>xp1>x,p2>up1>u,p2>vp1>v) X (p3>xp1>x,p3>up1>u,p3>vp1>v) if (x!=0) { NORMALIZE(x,y,z) p1>Tx += y/x; p1>Bx += z/x; p2>Tx += y/x; p2>Bx += z/x; p3>Tx += y/x; p3>Bx += z/x; } ....see webpage for full algorithm... Tom Vykruta Surreal Software 
From: Stuart Harrison <stuart.harrison@ku...>  20030224 17:15:59

Apologies if this has been posted recently (or at all).. this is my first post to the list (so go easy on me).. I find myself in need of a fast algorithm to calculate the length of a hermite (bezier) spline. My current method involves stepping small distances along the spline (using FFD) and noting the straightline distance between each adjacent point  this is both slow and innaccurate (well, it's probably accurate enough, but that's hardly the point). Can anyone help ? Aww, go on, you know you want to... Dino. Information contained in this email is intended for the use of the = addressee only, and is confidential and may be the subject of Legal = Professional Privilege. Any dissemination, distribution, copying or use = of this communication without prior permission of the addressee is = strictly prohibited.The views of the author may not necessarily = constitute the views of Kuju Entertainment Ltd. Nothing in this email = shall bind Kuju Entertainment Ltd in any contract or obligation.=0A= =0A= The contents of an attachment to this email may contain software = viruses which could damage your own computer system. While Kuju = Entertainment has taken every reasonable precaution to minimise this = risk, we cannot accept liability for any damage which you sustain as a = result of software viruses. You should carry out your own virus checks = before opening the attachment.=0A= 