Tom Melly wrote:

> Such an approach might work for simple primitives, but would fail on
> anything more complex - how do you define a sensible reference point for a
> blob?

I don't think anything is impossible - until proven, of course. My suggestion
for blob as well as CSG objects or other complex objects is the use of a
.subobject[] property, along with a .subobject_count. An example:

#declare ABlob = blob {
    threshold .65
    sphere { <.5,0,0>, .8, 1 pigment {Blue} }
    sphere { <-.5,0,0>,.8, 1 pigment {Pink} }
    finish { phong 1 }
  }

The blob object lends itself nicely to OO, like this:

ABlob
    -subobject_count
    -subobject[0]
        -type //sphere or cylinder
        -origin  // as it is a sphere
        -radius
        -strength
        -pigment
    -subobject[1]
        ..
    -finish

(If some of the blob items had been a cylinder, there had been .top and .bottom
properties of subobject[0] instead of .origin.)

This means we can access our blob as in this example:

#declare i=0;
#while(i<ABlob.subobject_count - 1)
    #if(ABlob.subobject[i].type=0)    // type 0 = sphere, 1 = cylinder
        // do something using subobject[i].origin
    #else
        // do something using subobject[i].top, subobject[i].bottom
    #end
    #declare ABlob.subobject[i].radius = ABlob.subobject[i].radius + 1;
    #declare ABlob.subobject[i].strength = ABlob.subobject[i].strength + i / 10;

    #declare i=i+1;
#end

A CSG example:

#declare ACSG = difference{
    box{1,-1}
    difference{
        sphere{0, 1}
        plane{y, 0}
        translate <1,0,0>
    }
}

ACSG
    -subobject_count
    -subobject[0]    //the box
    -subobject[1]    //the sphere - plane difference
        -subobject_count
        -subobject[0]    // the sphere
        -subobject[1]    // the plane

We could now access the plane down in the hierarchy by

ACSG.subobject[1].subobject[1]

Similar for meshes, unions of bicubic patches, etc.

----------------------------------------------------
Mikael Carneholm, B.Sc.
Dep. of Computer Science and Business Administration


Personal homepage:
http://www.studenter.hb.se/~arch
E-mail:
sa9### [at] idautbhbse

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