pyopengl-users

[PyOpenGL-Users] get Translation inside matrix stack

[Prashant S. <ani...@ya...>]

glPushMatrix()
glTranslate(5,0,0)
glTranslate(10,0,0)
glTranslate(5,0,0)
# How do I get here total increment of x axis(which is 5+10+5=20) before I Pop up.
glPopMatrix()



      

Re: [PyOpenGL-Users] get Translation inside matrix stack

[Gary H. <gh...@is...>]

Shantytown Saxena wrote:
>
> glPushMatrix()
> glTranslate(5,0,0)
> glTranslate(10,0,0)
> glTranslate(5,0,0)
> # How do I get here total increment of x axis(which is 5+10+5=20) 
> before I Pop up.
> glPopMatrix()

All the transformations are recorded by OpenGL in a 4x4 matrix.
You can recover that matrix like this:

    buff = (ctypes.c_double*16)()
    pyglet.gl.glGetDoublev(stack, buff)

If you started with the identity and did no other transformations you'll 
find the 20 in that 4x4 array.

In either the [0,3] or [3,0] element.  (I've forgotten which way Opengl 
stores the array now.)

Gary Herron


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Re: [PyOpenGL-Users] get Translation inside matrix stack

[Greg E. <gre...@ca...>]

Gary Herron wrote:

> All the transformations are recorded by OpenGL in a 4x4 matrix.
> You can recover that matrix like this:
> 
>     buff = (ctypes.c_double*16)()
>     pyglet.gl.glGetDoublev(stack, buff)

However, reading back the OpenGL matrix as part of your
rendering process isn't really a good thing to do, since
it requires waiting for any pipelined OpenGL commands
that you've sent to complete. This can slow things down
considerably.

If you're doing this a lot, it may be better to keep
track of the transformations yourself.

-- 
Greg