Thanks.
I guess my question would then be how do I convert from x,y,z to a,b,c using maths instead of glTranslatef/glRotatef?
Cheers
Astan

Zack Schilling wrote:
You cannot modify the matrix between glBegin and glEnd calls, so no  
translation or rotation between plotting of vertices is allowed.

If I understand what you want, you're trying to draw a line from the  
"camera" to an object. Depending on how your frustum is set up, this  
may be a bad idea. In any case, it'll look strange and glitchy at  
best. But if you insist, here's what you need to do.

Maintain the position of the camera with (x,y,z) and between loading  
the identity and doing any drawing, perform a glTranslatef(-x,-y,-z)  
as well as any other "camera" rotations you want. Once that's done,  
plot a line from (x,y,z) to (x1,y1,z1), where (x1,y1,z1) are the  
coordinates to the object you're drawing the line to.

            glBegin(GL_LINES)
            glVertex3f(x,y,z)
            glVertex3f(x1,y1,z1)
            glEnd()

You cannot and should not try to adjust the matrix while plotting  
points.

-Zack

On Jul 2, 2009, at 10:51 PM, Astan Chee wrote:

  
Hi,
I'm trying to draw a line between two points (x0,y0,z0 and x1,y1,z1)
like this:

           glPushMatrix()

           glEnable(GL_BLEND)

           glTranslatef(x,y,z)

           glRotatef(-angle[0],0,1,0)
           glRotatef(angle[1],1,0,0)

           glColor4f( 1, 0.0, 0.0, .8 )

           glBegin(GL_LINES)
           glVertex3f(x0,y0,z0)

           glTranslatef(-x,-y,-z)

           glRotatef(angle[0],0,1,0)
           glRotatef(-angle[1],1,0,0)

           glVertex3f(x1,y1,z1)
           glEnd()

           glDisable(GL_BLEND)
           glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
           glPopMatrix()

Where x0,y0,z0 is the point near or in front of the "camera" and the
point x1,y1,z1 is the point in "real world coordinates".
This doesn't seem to work. How should I be doing this assuming I don't
know how to calculate either point in terms of the other?
Thanks
Astan

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