OpenGL Rotation of an object around a line

Question

Hi, I am programming in OpenGL and C++. I know 2 points on 1 line ( a diagonal line) and wish to rotate an object around that diagonal line. How can I go about doing this? I know how to use glrotatef to rotate it around the x, y or z axis but am not sure about this Thanks Jessica

Answer 1

glrotate does the rotation about an axis. One method is to perform transformations which align rotation axis with one of coordinate axis, perform the rotation, then reverse the first step. If you need speed you can combine the operations into a special transformation matrix and apply them in one step. There's a description here.

Answer 2

The x, y and z parameters to glRotate can specify any arbitrary axis, not just the x, y and z axes. To find an axis passing through your line, just subtract the end-points of the line to get an axis vector: if the two points are (x1, y1, z1) and (x2, y2, z2), the axis you need is (x2-x1, y2-y1, z2-z1).

Edit: As @chris_l pointed out, this works only if the line passes through the origin. If not, first apply a translation of (-x1, -y1, -z1) so that the line passes through the origin, then apply the above rotation, and translate it back by (x1, y1, z1).