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Projection problems...

 
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Eib



Joined: 15 Apr 2009
Posts: 7
PostPosted: Wed Apr 29, 2009 2:44 pm    Post subject: Projection problems... Reply with quote
I'm trying to project world space coordinates to screen space with the following code.
Code:

        vfpu_identity_matrix(&temp_matrix);
        gumFastInverse(&temp_matrix,cam->view_matrix);

        vfpu_transform_vector(&temp_matrix,sun->position,&temp_vector4d);
        vfpu_transform_vector(cam->proj_matrix,&temp_vector4d,sun->screen);

        if (sun->screen->w!=0.0f) {
           w=1.0f/sun->screen->w;
           sun->screen->x=sun->screen->x*w;
           sun->screen->y=sun->screen->y*w;
           }
        sun->screen->x*=240.0f;
        sun->screen->y*=-136.0f;
        sun->screen->x+=240.0f;
        sun->screen->y+=136.0f;

        // All vectors are 4d. View and projection matrices are ok.
        // sun->position is a world-space position
        // sun->screen is a resulting screen-space position

Results are slightly incorrect. Can someone give a hint please where i made a mistake in this code ?
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Jim



Joined: 02 Jul 2005
Posts: 487
Location: Sydney
PostPosted: Wed Apr 29, 2009 9:43 pm    Post subject: Reply with quote
Well it's going to get quite cranky when screen->w is very near or equal to zero, or negative.

The best idea is to clip these polygons before you get anywhere near this stage in the pipeline.

Jim
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