I think you have misunderstood me. I do not "want quaternions" (I am
quite familiar with them in any case). What I want is code that does
for fixed-axis rotations what MouseRotate does for rotations around a
single point. (I think I can write such code myself, but I would
prefer to use something that has already been debugged and tested.)
KJ
Date: Wed, 27 Jun 2001 13:44:46 +0800
From: Chris Thorne <[EMAIL PROTECTED]>
So you want quaternions: where you specify a vector (axis) [X Y Z] and an angle W to
rotate about the axis.
I don't have this code (I'm sure a few on this list do) but you can look at:
http://www.cs.berkeley.edu/~laura/cs184/quat/quaternion.html
http://skal.planet-d.net/demo/matrixfaq.htm#Q45
This bit seems to be what you want:
Q47. How do I convert a quaternion to a rotation matrix?
--------------------------------------------------------
Assuming that a quaternion has been created in the form:
Q = |X Y Z W|
Then the quaternion can then be converted into a 4x4 rotation
matrix using the following expression:
| 2 2 |
| 1 - 2Y - 2Z 2XY - 2ZW 2XZ + 2YW |
| |
| 2 2 |
M = | 2XY + 2ZW 1 - 2X - 2Z 2YZ - 2XW |
| |
| 2 2 |
| 2XZ - 2YW 2YZ + 2XW 1 - 2X - 2Y |
| |
If a 4x4 matrix is required, then the bottom row and right-most column
may be added.
The matrix may be generated using the following expression:
----------------
xx = X * X;
xy = X * Y;
xz = X * Z;
xw = X * W;
yy = Y * Y;
yz = Y * Z;
yw = Y * W;
zz = Z * Z;
zw = Z * W;
mat[0] = 1 - 2 * ( yy + zz );
mat[1] = 2 * ( xy - zw );
mat[2] = 2 * ( xz + yw );
mat[4] = 2 * ( xy + zw );
mat[5] = 1 - 2 * ( xx + zz );
mat[6] = 2 * ( yz - xw );
mat[8] = 2 * ( xz - yw );
mat[9] = 2 * ( yz + xw );
mat[10] = 1 - 2 * ( xx + yy );
mat[3] = mat[7] = mat[11 = mat[12] = mat[13] = mat[14] = 0;
mat[15] = 1;
----------------
Chris
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