This is cut from a post of mine over in the images area that I think might
serve me better here.

I'm still playing with the Draw_Vistas option and I'm still not
sure if I need the -UR flag to be able to use my manual bounding
or not.

With these options (+UD +MB0) try the following:

  #include "colors.inc"
  camera {location <-500, 0, 0> look_at <0, 85, 0> angle 36}
  light_source { <110, 5, -500> White}

  #declare rear_tire = difference {
    sphere {<0, 85, 0>, 85 scale <1,1,.2>}
    cone {<0, 85, 20>, 50 <0, 85, -20>, 60}
    cone {<0, 85, -20>, 50 <0, 85, 20>, 60}
    bounded_by { box {<-85, 0, -13>, <85, 170, 13>} }
  }

  object {rear_tire pigment {Blue}}

Now comment out the bounded_by line. You'll be able to
see the difference even without the -UR flag.

However while playing with this code using the same options:

  #include "colors.inc"
  camera {location <0, 0, -500> look_at <0, 85, 0> angle 36}
  light_source { <110, 5, -500> White}

  #declare rear_tire = difference {
    sphere {<0, 85, 0>, 85 scale <1,1,.2>}
    cone {<0, 85, 20>, 50 <0, 85, -20>, 60}
    cone {<0, 85, -20>, 50 <0, 85, 20>, 60}
    bounded_by { box {<-85, 0, -13>, <85, 170, 13>} }
  }

  #declare rear_axle = sphere {<0, 85, 0>, 17}

  #declare rear_hub = difference {
    cylinder {<0, 85, 1>, <0, 85, -1>, 60}
    object {rear_tire}
    object {rear_axle}
    bounded_by { box {<-56, 29, -2>, <56, 141, 2>} }
  }

  object {rear_hub pigment {Blue}}

I note that even with the -UR flag on, the bounding slab
size doesn't visual change from the default.

Even replace the bounded_by line with this:
    bounded_by { box {<-50, 29, -2>, <56, 141, 2>} }
    clipped_by {bounded_by}

And you will see the shape is clipped but the bounding box
hasn't moved.  I'm using [800x600,AA 0.3] if that makes
a difference.

But if I replace it with:
    bounded_by { box {<0, 29, -2>, <56, 141, 2>} }
    clipped_by {bounded_by}

Now the bounding slap IS where it should be even without
the -UR flag.

I even tried this:
    bounded_by { box {<0, 29, -2>, <56, 1000, 2>} }
    clipped_by {bounded_by}

The shape is clipped BUT the bounding slap grew back in
the x-direction and NOT in the y-direction.  Why?

I get the smallest bounding slab and the shape I want if I
take the bounded_by statement off altogether and replace
the cylinder with:
cylinder {<0, 85, 1>, <0, 85, -1>, 56}

So this Draw_Vistas option isn't behaving in what I'd consider
a predictable manner.  Is what I've seen called the bounding
slab a 2D projection of the bounding box?  It sure looks like
something else when I use:

    bounded_by { box {<0, 29, -2>, <56, 1000, 2>} }
    clipped_by {bounded_by}

And see the object clipped and I see a short fat box when
I'd expect to see a thin tall box that extends to the top of
the screen.  Can anyone tell me what is going on here?

Post a reply to this message