Quaternion based rotation and pivot position
- by Michael IV
I can't figure out how to perform matrix rotation using Quaternion while taking into account pivot position in OpenGL.What I am currently getting is rotation of the object around some point in the space and not a local pivot which is what I want.
Here is the code [Using Java]
Quaternion rotation method:
public void rotateTo3(float xr, float yr, float zr) {
_rotation.x = xr;
_rotation.y = yr;
_rotation.z = zr;
Quaternion xrotQ = Glm.angleAxis((xr), Vec3.X_AXIS);
Quaternion yrotQ = Glm.angleAxis((yr), Vec3.Y_AXIS);
Quaternion zrotQ = Glm.angleAxis((zr), Vec3.Z_AXIS);
xrotQ = Glm.normalize(xrotQ);
yrotQ = Glm.normalize(yrotQ);
zrotQ = Glm.normalize(zrotQ);
Quaternion acumQuat;
acumQuat = Quaternion.mul(xrotQ, yrotQ);
acumQuat = Quaternion.mul(acumQuat, zrotQ);
Mat4 rotMat = Glm.matCast(acumQuat);
_model = new Mat4(1);
scaleTo(_scaleX, _scaleY, _scaleZ);
_model = Glm.translate(_model, new Vec3(_pivot.x, _pivot.y, 0));
_model =rotMat.mul(_model);//_model.mul(rotMat); //rotMat.mul(_model);
_model = Glm.translate(_model, new Vec3(-_pivot.x, -_pivot.y, 0));
translateTo(_x, _y, _z);
notifyTranformChange();
}
Model matrix scale method:
public void scaleTo(float x, float y, float z) {
_model.set(0, x);
_model.set(5, y);
_model.set(10, z);
_scaleX = x;
_scaleY = y;
_scaleZ = z;
notifyTranformChange();
}
Translate method:
public void translateTo(float x, float y, float z) {
_x = x - _pivot.x;
_y = y - _pivot.y;
_z = z;
_position.x = _x;
_position.y = _y;
_position.z = _z;
_model.set(12, _x);
_model.set(13, _y);
_model.set(14, _z);
notifyTranformChange();
}
But this method in which I don't use Quaternion works fine:
public void rotate(Vec3 axis, float angleDegr) {
_rotation.add(axis.scale(angleDegr));
// change to GLM:
Mat4 backTr = new Mat4(1.0f);
backTr = Glm.translate(backTr, new Vec3(_pivot.x, _pivot.y, 0));
backTr = Glm.rotate(backTr, angleDegr, axis);
backTr = Glm.translate(backTr, new Vec3(-_pivot.x, -_pivot.y, 0));
_model =_model.mul(backTr);///backTr.mul(_model);
notifyTranformChange();
}
