GIMP Version: 2.8.16
Operating System: Windows
GIMP Experience: Basic Level

List any relevant plug-ins or scripts:
Lights and Shadows / Perspective /

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I was trying to read/follow OMG's tutorial on Clear Glass Brumbies.
There is mentioned the use of the filter shown above

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(Lights and Shadows / Perspective) .
That filter allows the shadow to have an angle from 0 to 180, creating in any case the shadow behind the object.
I'm wondering whether:
- there is a similar filter with the possibility of shadow in front of the object (case when the sun is behind the object)
-- or --
- someone is able to find the source of that filter, analyze it and see whether it can be "extended" to work with angles from 0 to 360 (or from -180 to 180)
Thanks

That's interesting.
I'm not aware of any filter that does what you're asking.
It would make for a very nice addition to the already available lights and shadows filters.

Standard in Gimp: perspective-shadow.scm

Before

After


Is that it?


Edit 28-03-2016:

Appendix removed after the notes Ofnuts (OK) in the post (# 16)
Today I found the solution Graechan
http://gimpchat.com/viewtopic.php?f=9&t=9006

thanks a lot MareroQ !
But it didn't show in the standard sets of my Gimp functions.
Now I downloaded and installed the source you provided and it "replaced" the previous one.
Is it a "special version"?

edit: did "you" the change? if so, excellent and quick solution!

I have the impression that the perspective is not correct with the shadow in front of the object:
did the change only extend the rotation without changing the perspective computation ?
(if any, maybe there is no perspective computation, in spite of the filter's name)

it seems the perspective calculation is there, thus it should be changed also...

examples:

maybe this does what you want viewtopic.php?f=9&t=9006

unfortunately not, Tin
this one "looses" the part just in front of the object, so it's difficult to judge whether the perspective is correct

now I'm going to sleep.
Happy Easter to all Gimp-chatters:
- those who are already on Sunday (Australian)
- those who enter now the Sunday (Europe)
- those who have still to wait (America)
Happy Easter !

Is this what you want:

Old:
(half-bottom-width (/ select-width 2))

New:
(half-bottom-width (/ select-width 1.5))

Making the number larger makes the shadow come to more of a point. Smaller makes the shadow spread out.



And set at 1.25:

Yes, Steven, that's OK for shadow "in front of the object".
This modification of the script should be made ONLY when this is the case.
So far I didn't try to insert your modification into the code, but I guess that the statement should be conditioned:
-if angle > 180
else it should remain as it is for shadows behind.
I'll have a look (don't know if today, busy day).
Thanks for your indication.

I agree entirely. I just can't find a way to set that condition. The statement looks simple enough, but I can not understand how to implement it.

Hi Steven.

Maybe in this metod?


Edit 28-03-2016:

Appendix removed after the notes Ofnuts (OK) in the post (# 16)

downloaded and tried your version: I don't get any shadow

edit: it seems there is some "formal" error in the code (it doesn't start, practically)
I restored your original version

I could not find a way to work it into the script, so I cheated and made a second script. It shows under Perspective2 and is only for 181 degrees through 359 degrees. It shows as Perspective2 under Light and Shadow. Use Perspective for shadows behind and Persective2 for shadows in front.

I have uploaded the file with the corrected header information. Thank you ofnuts

This is open source, so modifying code and publishing your version is OK.

However, as a matter of etiquette you should clearly identify this version as yours, by changing the relevant info (header, and author/copyright in the registration data) because once it gets on the net, the origin of the modified version is quickly lost and people having problems with it will pester the original author.

Mentioning that this is derivative work and citing the original author is of course welcome...

Just fyi, that G'MIC also can do perspective shadow.

This does not work the same way. Even with a blank selection, the Perspective shadow will create a shadow based on that selection area, but when I try that with G'Mic, it does not produce anything. Actually, I could not get G'Mic to produce a shadow even with an image selection, using your same settings.

Yeah; and to toy a lot to get it to do this one.

Ah, I will have to give that a go when I get a chance. Thank you, sir!