Matrix cam, ocam;	// vanilla 4x4 matrix class
        Vector texcoords[4];	// vanilla 4 vectors

        ocam.getModelview();	// save the modelview matrix
        cam=ocam;		// copy it

        cam.c41=0.0;		// remove the translation part
        cam.c42=0.0;
        cam.c43=0.0;

        cam.invert3d();		// invert it, assuming some niceties

        glLoadIdentity();	// no modelview

        float x=maxd/mind;	// mind..maxd are depth range
        float y=aspect*x;	// aspect is aspect ratio (all from glFrustum)

	// here we generate texture coordinates that point along the
	// edges of the view frustum (ie including the rotation of
	// the view frustum, but no translation)

        texcoords[0]=cam*Vector(-1, aspect, -1);        // upper left
        texcoords[1]=cam*Vector(-1, -aspect,-1);        // lower left
        texcoords[2]=cam*Vector(1, -aspect, -1);        // lower right
        texcoords[3]=cam*Vector(1,  aspect, -1);        // upper right

        glDepthFunc(GL_ALWAYS);	// don't need to clear depth buffer
        glDisable(GL_LIGHTING);
        env.notify();		// this binds the cubemap texture
				// and sets the texture environment GL_REPLACE

        glBegin(GL_QUADS);			// just draw a full screen
        glTexCoord3fv(texcoords[0].xyz);	// quad using the method of your
        glVertex3f(-x, y, -maxd);		// choice.  I've used GL immediate
        glTexCoord3fv(texcoords[1].xyz);	// mode for clarity
        glVertex3f(-x, -y, -maxd);
        glTexCoord3fv(texcoords[2].xyz);
        glVertex3f(x, -y, -maxd);
        glTexCoord3fv(texcoords[3].xyz);
        glVertex3f(x, y, -maxd);
        glEnd();

        env.endnotify();	// turn off the texture
        glEnable(GL_LIGHTING);
        glDepthFunc(GL_LESS);	// normal depth buffering

        ocam.load();		// restore modelview