"[GDS|Entropy]" <gds### [at] hotmailcom> wrote:
> I've never used the trace function, or vlength...you wouldn't happen to have
> a link to an example would you?

Here's an example.  It should be pretty self-explanatory.  Six glows are drawn,
one on each face of a cube, and three are blocked.

 - Ricky





#version unofficial megapov 1.21;
#declare s = seed(123501);

// MACRO

/* Test whether a ray starting at start_pt and
 * ending at target_pt hits test_obj before it
 * gets there.  Returns either true if it reaches
 * it or false otherwise.  Add an extra epsilon
 * so that conindident points ARE drawn. */
#macro test_ray( start_pt, target_pt, test_obj )
    #local epsilon = 1.0e-10;
    #local nrml = <0,0,0>;
    #local direc = target_pt - start_pt;
    #local intersec = trace( test_obj, start_pt, direc, nrml );
    !(vlength(nrml) > 0 & vlength(direc) > vlength(intersec-start_pt)+epsilon)
#end

// SCENE

// Light/camera
light_source{ <15,25,-20> rgb 0.2 }
#declare cam_pt = <2.5,3.0,-3.5>;
camera{
    location cam_pt
    look_at 0
}

#macro draw_glow( pt, cam_pt, test_obj )
    #if(test_ray(cam_pt, pt, test_obj))
        glow{
            type 0
            location pt
            size 0.05
            radius 1.0
            fade_power 2
            color rgb vnormalize(<rand(s),rand(s),rand(s)>)
        }
    #end
#end

// Draw the objects
#declare thing = box{-1,1}
draw_glow(  x, cam_pt, thing )
draw_glow( -x, cam_pt, thing )
draw_glow(  y, cam_pt, thing )
draw_glow( -y, cam_pt, thing )
draw_glow(  z, cam_pt, thing )
draw_glow( -z, cam_pt, thing )
object{ thing pigment{rgb 1} }

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