[Papervision3D] matrix multiplication order
azupko at zupko.info
Fri May 8 08:01:10 PDT 2009
The order is important since matrix multiplication isn't commutative.
(Consider the differences of multiply row->colum and how its different
depending on which matrix is first). Essentially, the matrix in the
first position is applied "first". Think if you want to apply a
rotation and translation on an object. If you do translate*rotation,
your object will be "moved", then rotated, meaning your object will
rotate around the translated center rather than its original origin.
If you do rotate*translate, you would rotate around its center, then
move out from there.
consider code (not sure if this is correct, but you can fix the syntax
sphere.transform.calculateMultiply4x4(Matrix3D.rotationMatrix(0, 1, 0,
Math.PI/2), Matrix3D.translationMatrix(300, 0, 0));
This code will rotate the sphere (around origin of scene) 90 degrees
and move it down its new X axis (which is now the Z axis in world space)
If you flip those two params, it will move out to the right, and then
rotate around its new center.
hopefully that will help somewhat - a more thorough explanation might
On May 8, 2009, at 9:24 AM, grizu wrote:
> Could someone tell me, what is the difference between:
> do3d.transform.calculateMultiply3x3 (do3d.transform,
> do3d.transform.calculateMultiply3x3 (rotationMatrix,
> I know that order is important, when multiplying matrices (rotX,
> rotY, rotZ,
> then translation, is this right?). But I can't understand, what is
> going on
> here. I tried the first thing, which seems logic to me: I simply
> multiply an
> object's transform with a rotation matrix. But my simple scene only
> with the second way.
> It would be very nice, if someone could explain this to me. I try to
> into this matrix-thing, but it is not easy sometimes...
> Thanks in advance!
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