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Absolute Axis

by Phillip O'Shea · in Torque Game Engine · 02/20/2008 (12:13 pm) · 3 replies

Howdy,

I've got an object that I want to rotate. At the moment I am doing this:

MatrixF ourTransform = getTransform();

EulerF  reffAxis(rotationAxis * angle);
MatrixF reffMat(reffAxis);
 
ourTransform.mul(reffMat);
 
setTransform(ourTransform);

My problem is that when I change the axis I am rotating it on, it uses the internal axis. For example: I rotate 180 degrees around the x-axis, so that the object's base is now on top. I then rotate it 45 degrees around the y-axis and it has rotated the wrong way.

Is there a method where I can rotate an object around the normal axis and not the object's own? I am thinking that i have to somehow find the object's orientation before I transform it, but how do I do this?

Cheers
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Associate Phillip O'Shea
Violent Tulip

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    Associate Phillip O'Shea
    Violent Tulip
    #1
    02/24/2008 (11:14 pm)
    Maybe I didn't make myself too clear.

    When you rotate an object using matrix multiplication, you always use the object's current rotation as a reference for the next rotation being applied.

    When the rotation is (0 0 0) the matrix looks like this:
    1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1

    When you rotate the object around the x-axis by 90 degrees, it should look something like this (I think there is meant to be a negative 1 in there somewhere, but I forget):
    1 0 0 0
0 0 1 0
0 1 0 0
0 0 0 1

    If I want to now rotate the object around the world's z axis, then I have to rotate the object using its y-axis. Obviously I can use the transformation matrix to see what the rotation axis *should* be, I just don't know howI should go about doing it.

    Associate Orion Elenzil
    Real Life Plus
    #2
    02/25/2008 (12:13 am)
    Maybe try
    reffMat.mul(ourTransform);
setTransform(reffMat);
    ?

    you might need/want to strip any translation out of the matrix tho.
    perhaps something like this: (exact syntax probably off)
    m1 = getTransform();
   p1 = m1.getColumn(3); // translation
   m1.setColumn(3, Point3F(0, 0, 0));
   m2 = worldSpaceRotationMatrix;
   m2.mul(m1);
   m2.setColumn(3, p1);
   setTransform(m2);

    Associate Phillip O'Shea
    Violent Tulip
    #3
    02/25/2008 (1:04 am)
    Still suffers from the same problem.

    In my example, rather than creating a matrix for z-axis rotation using something that looks like:
    MatrixF reffMat(0.0f, 0.0f, angle);

    I need:
    MatrixF reffMat(0.0f, angle, 0.0f);