围绕任意轴旋转平面2d对象

Question

So I have a flat 2d Polygon and I would like to rotate each point of the Polygon around a axis defined by two 2d Points. These rotated points are later used to generate a 3d rotations object from the flat 2d Polygon. So I got this at the moment:

1. Calculate the axis normal position of one polygon point.
2. From this point I calculate the matrix with a matrixLookAt(pointOnLine, polygonPoint, upVec) function
3. Then I rotate the matrix on the Z-Axis with 45°
4. And finaly I multiply the polygonPoint with the computed matrix.

But with this method I don't get any usefull results.

For better unterstanding: P1 & P2 are defining the axis Psrc is the polygonPoint and Pdest is the final point in 3d

Answer 1

Far easier to be done. Just modify your model matrix before drawing using glRotatef() :

glRotatef(angle, vx, vy, vz);

• angle is obviously the angle.
• vx , vy , and vz are the vector defining your rotation axis.

Or, to use it with 2 points given:

glRotatef(p1.x - p2.x, p1.y - p2.y, p1.z - p1.z);

If your rotation axis doesn't go through your world's origin, you'll have to adjust everything so your axis goes through the origin using glTranslatef() :

glTranslatef(-p1.x, -p1.y, -p1.z); // move one point on the vector into the origin
glRotatef(p1.x - p2.x, p1.y - p2.y, p1.z - p1.z); // rotate everything
glTranslatef(p1.x, p1.y, p1.z); // move everything back into position