Grease Pencil: Holdout Material should work across different GPencil objects #120560

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Lukas W · 2024-04-12T12:07:26+02:00

Lukas W commented

2024-04-12 12:07:26 +02:00

System Information
Operating system: Ubuntu 23.10
Graphics card: nVidia GeForce MX150

Blender Version
Broken: 4.1
Worked: never

Short description of error

Activating the checkbox "Holdout" on a Grease Pencil material successfully hides strokes and fills within the same objects according to layer order, but does not meaningfully affect those in another object.

Exact steps for others to reproduce the error
Render the attached file gp_holdout.blend . Note that line crossing the vowel in both the words "Front" and "Back" is invisible inside the counter of the letter. Note that none of the strokes in the object "Back" is hidden inside the "o" of "Front", however. Toggle "Stroke Depth Order" on both of the objects and re-render to confirm that this is not remedied by this setting.

Reasoning
The design of Blender and Grease Pencil encourages putting backgrounds and characters into different objects.
Compositing of 2D animation might require separate passes with strokes and fills only. Simply moving all fills to another View Layer is helpful, but leaves an incorrect pass for the strokes, because strokes in the back are not correctly hidden by fills in the front. This can be solved using Holdout materials for scenes with a single GP object, but not for scenes using multiple, overlapping GP objects.

Proposed solution
Add two toggles to Material -> Surface -> Fill under "Holdout" with the name "Affects" "same object" (checked by default) and "other objects" (unchecked by default). Draw accordingly. Whether GP Holdout materials also affect non-GP objects can depend on what is more convenient to implement.

**System Information** Operating system: Ubuntu 23.10 Graphics card: nVidia GeForce MX150 **Blender Version** Broken: 4.1 Worked: never **Short description of error** Activating the checkbox "Holdout" on a Grease Pencil material successfully hides strokes and fills within the same objects according to layer order, but does not meaningfully affect those in another object. **Exact steps for others to reproduce the error** Render the attached file gp_holdout.blend . Note that line crossing the vowel in both the words "Front" and "Back" is invisible inside the counter of the letter. Note that none of the strokes in the object "Back" is hidden inside the "o" of "Front", however. Toggle "Stroke Depth Order" on both of the objects and re-render to confirm that this is not remedied by this setting. **Reasoning** The design of Blender and Grease Pencil encourages putting backgrounds and characters into different objects. Compositing of 2D animation might require separate passes with strokes and fills only. Simply moving all fills to another View Layer is helpful, but leaves an incorrect pass for the strokes, because strokes in the back are not correctly hidden by fills in the front. This can be solved using Holdout materials for scenes with a single GP object, but not for scenes using multiple, overlapping GP objects. **Proposed solution** Add two toggles to Material -> Surface -> Fill under "Holdout" with the name "Affects" "same object" (checked by default) and "other objects" (unchecked by default). Draw accordingly. Whether GP Holdout materials also affect non-GP objects can depend on what is more convenient to implement.

gp_holdout.blend

1.1 MiB

Lukas W added the

labels 2024-04-12 12:07:26 +02:00

Lukas W commented

2024-04-12 14:32:40 +02:00

Related report: #89879

Pratik Borhade commented

2024-04-15 07:58:34 +02:00

Hi, thanks for the report. Can confirm.
cc @antoniov

Hi, thanks for the report. Can confirm. cc @antoniov

Pratik Borhade added

and removed

labels 2024-04-15 07:58:49 +02:00

Antonio Vazquez commented

2024-04-15 09:42:39 +02:00

IIRC this is by design and the hold out works by object, @fclem can you confirm?

Clément Foucault commented

2024-04-15 10:26:44 +02:00

I can confirm. The holdout only exists because we needed to support holes in fills. It might even be removed if we add support for that at the geometry level.

Clément Foucault closed this issue

2024-04-15 10:26:47 +02:00

Blender Bot added

and removed

labels 2024-04-15 10:26:49 +02:00

Lukas W commented

2024-04-15 10:50:44 +02:00

In that case I do agree it should be removed, at least as a user-facing option. Stroke holdouts and coloured holdouts make little sense, if their only purpose is to create fully transparent holes on the same layer.

BTW, other software packages use blend modes to achieve the effect that Holdout has now. TVPaint has the "Erase" mode, for example, as I am sure others have as well under different names. Blend modes in Grease Pencil already act within the current object only, so the result of a new erasure blend mode would be more intuitive than the current Holdout material option.

In that case I do agree it should be removed, at least as a user-facing option. Stroke holdouts and coloured holdouts make little sense, if their only purpose is to create fully transparent holes on the same layer. BTW, other software packages use blend modes to achieve the effect that Holdout has now. TVPaint has the "Erase" mode, for example, as I am sure others have as well under different names. Blend modes in Grease Pencil already act within the current object only, so the result of a new erasure blend mode would be more intuitive than the current Holdout material option.

Clément Foucault commented

2024-04-15 11:01:53 +02:00

Blend modes in Grease Pencil already act within the current object only, so the result of a new erasure blend mode would be more intuitive than the current Holdout material option.

That does sounds way more intuitive and easier to implement (and manage) in the renderer. I believe this is the way to move this feature. Ping @filedescriptor

> Blend modes in Grease Pencil already act within the current object only, so the result of a new erasure blend mode would be more intuitive than the current Holdout material option. That does sounds way more intuitive and easier to implement (and manage) in the renderer. I believe this is the way to move this feature. Ping @filedescriptor

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YimingWu reopened this issue

2024-04-16 05:01:32 +02:00

Blender Bot added

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labels 2024-04-16 05:01:35 +02:00

YimingWu added

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