[OpenSCAD] Negative ghosts

nop head nop.head at gmail.com
Fri Sep 23 20:07:53 CEST 2011


Thanks, I tried to make a simple test case but I couldn't get it to
happen. It happens all the time in my models though. For example I
model a stepper motor with rounded corners by intersecting a cube with
a  cylinder. It looks fine on its own but if I draw it resting on a
surface I can see the shadow of the cylinder on the surface unless I
offset it slightly. The bodge factors I am adding get bigger and
bigger. I started with 0.01 but I am up to 0.03 in places now which is
approaching the accuracy of the print.

It does look like Z-buffer effects. I hadn't realised that is how
opencsg works. I am surprised it is so slow if it uses graphics
hardware. How does a few thousand primitives trouble a modern graphics
card? Surely it should do millions of triangles per second and
billions of pixels.

On 23 September 2011 02:29, William Adams <william_a_adams at msn.com> wrote:
> You can see the problem on this thing: http://www.thingiverse.com/thing:8661
>
> Render the two halves at the exact same thickness.  Here it shows up by the
> color of the deleted part still being applied to the other piece.  I think
> it's actually a problem with OpenCSG.
>
> -- William
>
> ===============================
> - Shaping clay is easier than digging it out of the ground.
>
>
> http://internationalwilliam.spaces.msn.com/
>
>
> ________________________________
> Date: Thu, 22 Sep 2011 22:33:49 +0100
> From: giles.bathgate at gmail.com
> To: openscad at rocklinux.org
> Subject: Re: [OpenSCAD] Negative ghosts
>
> I think I know what you mean but an example scad script would still be good
> for reference.
> On Sep 22, 2011 10:28 PM, "nop head" <nop.head at gmail.com> wrote:
>> If I make an object using difference() or intersection() to remove
>> part of it then the object looks fine in opencsg but if I place it
>> next to another object such that the subtracted part is coincident
>> with the face of another object then the negative object becomes
>> visible. Is this a bug in opencsg or openscad?
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