[PyOpenGL-Users] Picking using SelectBuffer

[Simon W. <sim...@gm...>]

I'm trying to use glRenderMode(GL_SELECT) to implement picking. The
problem is, almost all picking examples deal with 3D projection
(gluPerspective), whereas I am using glOrtho, so I suspect I need to
do something different.

The below code doesn't work, it accumulates hits in the select buffer,
but they are not the hits I expect. Any pointers on where I might be
going wrong?

Also, is there a simple way to get OpenGL to render a small box on the
screen which shows exactly which region is being picked?

Thanks for any help...=20

Sw.


    def pick(self, position):
        glInitNames()
        glSelectBuffer(64)
        glRenderMode(GL_SELECT)
        glMatrixMode(GL_PROJECTION)
        glPushMatrix()
        glLoadIdentity()
        viewport =3D glGetIntegerv(GL_VIEWPORT)
        n_w,n_h =3D display._screen.dimensions
        glOrtho(-n_w,n_w,-n_h,n_h,1,0)
        gluPickMatrix(position[0],viewport[3]-position[1],3,3,viewport)
        glMatrixMode(GL_MODELVIEW)
        for index, i in enumerate(self.items):
            glPushName(index)
            display._screen.blit(i.item, i.position)
            glPopName()
        glMatrixMode(GL_PROJECTION)
        glPopMatrix()
        glMatrixMode(GL_MODELVIEW)
        glFlush()   =20
        items =3D []
        for hit in glRenderMode(GL_RENDER):
            items =3D items + [self.items[i] for i in hit[2]]
        return items