scottishrob41 nous illumina en ce 2008/04/28 16:58 -->
> Howdy Pov-Rayers. I was curious about something I discovered while trying to
> create a difference with a cylinder and a hollow box. When I try to use the
> cylinder to open a hole in one side of the box, I notice the cylinder is still
> visible as if I had just merged them together. I figured out playing around
> with it, that the only way to get the cylinder to dissappear and leave the
> difference hole in the box is to assign a 'Clear' pigment to the cylinder. Has
> anyone else noticed this? Is this to be expected or is it a bug of some sort?
> FYI, I am running both version 3.6.1 and the beta 3.7 on a dual core system with
> 1 gb Ram. Both versions give the same result. I hope someone out there can shed
> some light on this. THNX.
> 
> 

Not a bug, working as expected.

You start with a box. Think of that box as a solid block of some material. When 
you use the difference, it's like you carve that shape out of the first object. 
In your case it's like driling a hole into a solid block.

If you want an infinitely thin shell, using "clipped_by" or assining a clear 
pigment to the carving object is the way to go.

If you want your side to have some thickness, add a second, slightly smaller, 
box to carve out the inside of the big box.
Sample:
difference{
	box{10,-10} // The box itself
	box{9,-9} // the empty space inside the box
	cylinder{8*x,11*x, 8} // A nice big hole in one of the sides
	texture{Some_Texture}
	rotate A_Rotation
	translate Somewhere
	}

A note about the "hollow" key word: it sole and only purpose it to allow an 
object to contain a media and to allow fog to exist inside of it. Nothing else.

-- 
Alain
-------------------------------------------------
OFFICE ARITHMETIC
Smart boss + smart employee = profit
Smart boss + dumb employee = production
Dumb boss + smart employee = promotion
Dumb boss + dumb employee = overtime

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