Hello,
huiliang yang wrote:
I have a question about computeLocalToWorldMatrix in camera class.
First, since the openscenegraph use row matrix instead column matrix
like opengl, I thought the default matrix multiply should be post
multiply so that :
V' = M*V (opengl premultiply) chanage to
V' = VT*MT ( osg post multiply)
Ok
but looks like the camera still use pre_multiply as default, but the
_viewmatrix define in camera class is apparently is a row matrix MT.
How do you get to this statement, which section of the code do you refer to?
It also depends on your definition of 'pre-multiply'. If you say VT*MT
is "post multiply" (as you do above), then this implies that you
actually mean "MT post-multiplies VT". This is turn also means that "VT
pre-multiplies MT". So it depends from which operand you look at it how
you describe the operation.
Second, even as the default pre_multiply, then let's say:
V' = M*V if (_transformOrder==PRE_MULTIPLY)
then its inverse should be
V = M-1* V' ,
why in function computeWorldToLocalMatrix
Which class? You say "V", which implies a vector usually, but, for
example, Camera::computeWorldToLocalMatrix works on a matrix as input.
If you indeed refer to Camera::computeWorldToLocalMatrix() then I would
say that that method does the inverse operation of
computeLocalToWorldMatrix(). Assuming _referenceFrame==RELATIVE_RF and
_transformOrder==PRE_MULTIPLY then the method computeLocalToWorldMatrix
pre-multiplies its argument "matrix" with "_viewMatrix". I.e.
matrix.preMult(_viewMatrix);
actually does
matrix = _viewMatrix * matrix;
Method computeWorldToLocalMatrix() does the inverse of this operation,
so instead of pre-multiplying with _viewMatrix it post-multiplies with
the inverse of _viewMatrix (the comments also say this).
Regards,
Paul
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