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How does setEulerZYX function work?
Posted: Thu Feb 12, 2015 6:02 pm
by Manish Bista
I have been looking into the RagdollDemo and have kind of got stuck in the part where setEulerZYX() is used in basis matrix.
Code: Select all
transform.setIdentity();
transform.setOrigin(btVector3(btScalar(-0.35), btScalar(1.45), btScalar(0.)));
transform.getBasis().setEulerZYX(0,0,M_PI_2);
m_bodies[BODYPART_LEFT_UPPER_ARM] = localCreateRigidBody(btScalar(1.), offset*transform, m_shapes[BODYPART_LEFT_UPPER_ARM]);
I did some research, yet couldn`t understand what exactly does this function do and why it is needed. Any help would be very nice.
Re: How does setEulerZYX function work?
Posted: Fri Feb 13, 2015 12:45 am
by drleviathan
The code is using btMatrix3::setEulterZYX(x, y, z) to build a 3x3 matric whose values represent a rotation of PI/2 (aka 90 degrees) about the z-axis. The rotation is being used to initialize the transform of the btRigidBody that corredponds to the upper left arm.
The upper left arm is probably using a btCapsule shape, which means by default its axis lies parallel to the y-axis (up). After a 90 degree rotation about the z-axis (using the
right hand rule) the capsule should lie parallel to the x-axis, pointing in the negative direction.
Try changing the angle value from
1.0 * M_PI_2 to be
0.5 * M_PI_2 or
0.25 * M_PI_2 to see how it changes the position of the left arm.
