**comp.graphics.algorithms**

## Subject: **Re: using glVertex*() in a second coordinate frame**

Thank you very much. In the glLoadMatrix command, will the matrix I'm

passing in have the origin of the particle or the negative of the origin?

In other words, instead of origin.x, origin.y and origin.z should it

be -origin.x, -origin.y and -origin.z? I remember seeing negatives in this

context, but am not 100% sure....

Thanks again for your help.

> Push the current coordinate system on the stack (glPushMatrix) then

> transform the coordinate system to the particle frame (either

> glMultMatrix or glLoadMatrix depending whether the particle coordinates

> are resp. to current coordinates or not). The matrix you need to pass

> consist of three vectors beeing the local axes and the last column

> being the particle position (but be aware that OpenGL uses column-major

> convention).

>

> Now you can define the coordinates with respect to the particle frame.

>

> And don't forget to get back to the previous frame (glPopMatrix) at the

> end :-)

>

> Przemek

>

> --

> "Beauty is the first test: there is no permanent place

> in the world for ugly mathematics." G.H. Hardy

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