[visionegg] Re: GL state responsibility (warning: may contain theory)
- From: Tony Arkles <tony@xxxxxxxxx>
- To: visionegg@xxxxxxxxxxxxx
- Date: Wed, 13 Jul 2005 15:41:20 -0600
Bertrand Guay-Paquet wrote:
You are right about your assessment that stimuli positioning should be
done this way:
-glPushMatrix()
-glTranslatef(position_of_stimulus)
-stimulus.draw()
-glPopMatrix()
This is what we have been thought in computer engineering classes at
any rate. The positioning should be done in a hierarchical way when
drawing multipart scenes. This is not currently the case with every
stimulus calling glLoadIdentity().
Just wanted to contribute a little to the discussion.
You mention that you use the GL_PROJECTION matrix to point the camera?
I'd be curious to know how you do it!
Right now if you look at the Projection class (in Core.py), it
illustrates what is being done. Essentially there are a series of
functions (translate, rotate, look_at, etc...) that all just act on the
GL_PROJECTION matrix. Here's an example:
def translate(self,x,y,z):
"""Compose a translation and set the OpenGL projection matrix."""
gl.glMatrixMode(gl.GL_PROJECTION) # Set OpenGL matrix state to
modify the projection matrix
gl.glLoadMatrixf(self.parameters.matrix) # Need PyOpenGL >= 2.0
gl.glTranslatef(x,y,z)
self.parameters.matrix = gl.glGetFloatv(gl.GL_PROJECTION_MATRIX)
From what I understand, it's recommended (by the OpenGL people) that
all this be done on the GL_MODELVIEW matrix instead of the GL_PROJECTION
matrix for all of the stimuli. I think that as long as we don't have
too complex of a scene (to overflow the glPushMatrix() stack), the
hierarchy method would be a lot more flexible.
Tony
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