difference between preview & render

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difference between preview & render

boxcarmib
historically i’ve always enjoyed seeing what is previewed being what I got with rendering. updating an older project I spent hours tracking down a bug that turned out to not be a bug, but simply that F5 wasn’t giving me what F6 was.
So I’m just looking for suggestions for what I may be doing wrong, or what F6 will do that F5 won’t and perhaps some defensive coding practices that might help me to avoid this situation in future.
I would present the code but it’s quite long and is very customized with my own openSCAD extensions and library so I don’t think it would serve much purpose.
However, I attach two outputs… one of the preview and one of the render… exact same file.
Any suggestions?


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Re: difference between preview & render

MichaelAtOz
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> a bug that turned out to not be a bug, but simply that F5 wasn’t giving me
what F6 was.

How do you know it's not a bug? Either in OpenSCAD or ... your code?

F5 should, mostly#, give you what F6 does, in terms of shapes except the
tessellation (how it draws the triangles/quads making the shape*) can be
different.

In this case it appears the difference on the right of the object doesn't
seem to happen in F5 (assuming the left image is F5). There could be reasons
for that, without looking at the code it is hard to say.

# Some things can affect preview, such as
- needing 'convexity' on extrudes, some poly's, surface, render, import;
often that shows as visual oddities.
- some zoom related views dealing with large objects & difference
- ...others I can't recall ATM...

[* I really don't like this development, you used to be able to rely on the
point/edge in F5 being THE same point/edge on render...mutter...mutter...]



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* on the Forum, click on my MichaelAtOz label, there is a link to email me.

Unless specifically shown otherwise above, my contribution is in the Public Domain;
to the extent possible under law, I have waived all copyright and related or neighbouring rights to this work.
Obviously inclusion of works of previous authors is not included in the above.
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Re: difference between preview & render

boxcarmib
Yes, you’re right, the left image(blue) is preview and the green is render.

The object being produced is part of a 3d printed nutcracker soldier i crank out every year. I make stylistic changes to make it somewhat different every year… and this has led to increasingly tortuous code… so NEXT year I should do what I intended to do and refactor the whole thing. That will not only result in cleaner code, but I can keep an eye on this annoying different in preview/render behaviour and I hopefully be able to spot what kind of operation causes the difference in behaviour.

Thanks for your comments. :)

The nature

> On Dec 6, 2020, at 6:17 PM, MichaelAtOz <[hidden email]> wrote:
>
>> a bug that turned out to not be a bug, but simply that F5 wasn’t giving me
> what F6 was.
>
> How do you know it's not a bug? Either in OpenSCAD or ... your code?
>
> F5 should, mostly#, give you what F6 does, in terms of shapes except the
> tessellation (how it draws the triangles/quads making the shape*) can be
> different.
>
> In this case it appears the difference on the right of the object doesn't
> seem to happen in F5 (assuming the left image is F5). There could be reasons
> for that, without looking at the code it is hard to say.
>
> # Some things can affect preview, such as
> - needing 'convexity' on extrudes, some poly's, surface, render, import;
> often that shows as visual oddities.
> - some zoom related views dealing with large objects & difference
> - ...others I can't recall ATM...
>
> [* I really don't like this development, you used to be able to rely on the
> point/edge in F5 being THE same point/edge on render...mutter...mutter...]
>
>
>
> -----
> OpenSCAD Admin - email* me if you need anything,  or if I've done something stupid...
>
> * on the Forum, click on my MichaelAtOz label, there is a link to email me.
>
> Unless specifically shown otherwise above, my contribution is in the Public Domain; to the extent possible under law, I have waived all copyright and related or neighbouring rights to this work. Obviously inclusion of works of previous authors is not included in the above.
>
> --
> Sent from: http://forum.openscad.org/
>
> _______________________________________________
> OpenSCAD mailing list
> [hidden email]
> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org


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