Re: Implementation of a pitch ladder.

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Ran Yakir (rany++at++bvr.co.il)
Wed, 17 Jan 1996 07:57:23 +0000

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In reply to: d3++at++po.iijnet.or.jp: "1.2 & 2.0"

>
> The conversion from screen to world coordinates is taking
> up time, and also appears a little shaky. I am considering
> whether I need to move this to an overlay plane. I am leery
> to do this since I am working in a GLX window, and have never
> used overlays in that configuration.

The way to do this as follows :

In the channel draw callback :

....

pfDraw();

#ifdef IRISGL
        mmode (MPROJECTION);
        ortho2 (-1.0, 1.0, -1.0, 1.0);
        mmode (MVIEWING);
        pfPushIdentMatrix();

        /*
         * Now, you have a coordinate system which correspondes to viewport
         * coordinates
         */

        pfPushState();
        pfBasicState(); /* no transparency, texture, etc. */
        zbuffer (FALSE);

        bgnline();
        v2f( ...)
        ....
        endline();

        zbuffer (TRUE);
        pfPopState();
        pfPopMatrix();

#else

        glMatrixMode (GL_PROJECTION);
        glLoadIdentity();
        gluOrtho2D (-1.0, 1.0, -1.0, 1.0);

glMatrixMode (GL_MODELVIEW);
glLoadIdentity();

        pfPushState();
        pfBasicState(); /* no transparency, texture, etc. */
        glDisable (GL_DEPTH_TEST);
        glBegin (...);
        ....

glEnd();

glEnable (GL_DEPTH_TEST);
pfPopState();
#endif

If you want you 3D coordinate system later, you might want to save the
projection matrix (in IrisGL) or push it (in OpenGL), and retrieve it later.

Overlay has nothing to do with coordinate system. You might go into overlay and
continue drawing with the same 3D transformations.

Ran

-- 
 __                                  | Ran Yakir
 /_)  _  __   \  / _   / o __        | Graphics App. Chief Engineer
/ )_ (_(_) )   \/ (_(_/<_(_)(        | BVR Technologies Ltd.
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