## gl 3d rotation of parent child shapes

Mar 19 2006 | 12:42 pm
hope someone with trig or linear algebra knowledge can clarify this for me seems like for years Ive stumbled on deriving the xyz cordinates of a cylinder's tip so I can bind it seemlessly to other shapes as arms or tendrils. this patch shows my appraoch to the problem and can be aded to a gl.sketch environment, it uses jasch's rotatexyz to attempt to bind a sphere to a cylinders end, I just cant get it to bind when xy and z are actively rotating, I use a half black half white texture to make the cylinder half invisible for simplicity, the shape orient command is scaled and moded into pi phases it seems like the shape orient and the xyzrotate just arn't in the same coordinate system, and that there is some constant attenuation that needs to be made to get them to agree, siggraph site has these equations but I dont know how to translate math matri in my head anymore let alone into max, can someone drop me a patch or mod mine so I can jump this hurdle get back into the art of things
Z-axis rotation is identical to the 2D case: x' = x*cos q - y*sin q y' = x*sin q + y*cos q z' = z
( cos q sin q 0 0) Rz (q) = (-sin q cos q 0 0) ( 0 0 1 0) ( 0 0 0 1)
X-axis rotation looks like Z-axis rotation if replace: X axis with Y axis Y axis with Z axis Z axis with X axis So we do the same replacement in the equations: y' = y*cos q - z*sin q z' = y*sin q + z*cos q x' = x
(1 0 0 0) Rx(q) = (0 cos q sin q 0) (0 -sin q cos q 0) (0 0 0 1)
Y-axis rotation looks like Z-axis rotation if replace: X axis with Z axis Y axis with X axis Zaxis with Y axis So we do the same replacement in equations : z' = z*cos q - x*sin q x' = z*sin q + x*cos q y' = y
(cos q 0 -sin q 0) Ry(q) = (0 1 0 0) (sin q 0 cos q 0) (0 0 0 1)

• Mar 19 2006 | 11:46 pm
Hi Derek,
The easy way to handle this is use the transform matrix rather than calculating the 4x5 modelview matrix by hand. Please see the OpenGL Redbook (html/pdf of v1.1 available at www.opengl.org), or the various online tutorials on OpenGL modelview matrix manipulation for more information. You can then avoid having to calculate the 4x4 modelview matrix values explicitly. The important sketch commands you will want to familiarize yourself with are:
glmatrixmode glpushmatrix glpopmatrix gltranslate glscale glrotate
Hope this points you in the right direction.
-Joshua