Holdout Fill not working as expected with Grease Pencil #89879

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Alasdair Beckett-King · 2021-07-15T16:22:36+02:00

2021-07-15 16:22:36 +02:00

Operating system: Win 10
Graphics card: Nvidia GTX 1060

Broken: 2.93
Worked: unknown

I would expect holdout fills to render as 100% transparent. In Blender's image viewer, they don't - their opacity seems to change based on how bright they are, so white is 100% opaque, but grey is semi-transparent.

Saving the same image to a PNG file, the holdouts are fully transparent, but with aliased artefacts around the edge of the surrounding black strokes, in the colour of the holdout fill. If there is another grease pencil object positioned behind the holdout fill, instead of vanishing, its strokes are tinted the colour of the holdout fill.

(The artefacts are more noticeable against a dark or checkered background.)

Try rendering the simple drawing in the attached .blend, exporting a PNG and examining it in an image editor. holdouttest.blend

Operating system: Win 10 Graphics card: Nvidia GTX 1060 Broken: 2.93 Worked: unknown I would expect holdout fills to render as 100% transparent. In Blender's image viewer, they don't - their opacity seems to change based on how bright they are, so white is 100% opaque, but grey is semi-transparent. Saving the same image to a PNG file, the holdouts are fully transparent, but with aliased artefacts around the edge of the surrounding black strokes, in the colour of the holdout fill. If there is another grease pencil object positioned behind the holdout fill, instead of vanishing, its strokes are tinted the colour of the holdout fill. ![holdout.png](https://archive.blender.org/developer/F10225196/holdout.png) (The artefacts are more noticeable against a dark or checkered background.) Try rendering the simple drawing in the attached .blend, exporting a PNG and examining it in an image editor. [holdouttest.blend](https://archive.blender.org/developer/F10225159/holdouttest.blend)

Alasdair Beckett-King commented

2021-07-15 16:22:36 +02:00

Added subscriber: @Alasdair-1

Philipp Oeser commented

2021-09-15 15:42:05 +02:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2021-09-15 15:42:05 +02:00

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Philipp Oeser commented

2021-09-15 15:42:05 +02:00

This looks wrong, but I am not sure I understand fill holdout correctly.
Guess #grease_pencil module devs needs to check.

This looks wrong, but I am not sure I understand fill holdout correctly. Guess #grease_pencil module devs needs to check.

Antonio Vazquez commented

2021-09-15 15:44:50 +02:00

Added subscribers: @fclem, @antoniov

Antonio Vazquez commented

2021-09-15 15:44:50 +02:00

@fclem could you review this? you know better than me this part of the code.

Antonio Vazquez commented

2021-09-15 15:49:33 +02:00

IIRC this is the expected result according to the current design. The full transparent is only when you use full black color. Any other color will mix the color with the existing one. Also, you can modulate the transparency using the alpha value of the color.

We will wait for @fclem to confirm it before archive the task report.

IIRC this is the expected result according to the current design. The full transparent is only when you use full black color. Any other color will mix the color with the existing one. Also, you can modulate the transparency using the alpha value of the color. We will wait for @fclem to confirm it before archive the task report.

Alasdair Beckett-King commented

2021-09-15 15:52:31 +02:00

Being able to modulating the opacity of the holdout makes sense, but surely tinting strokes and leaving artefacts in the colour of the holdout isn't expected behaviour?

Being able to modulating the opacity of the holdout makes sense, but surely *tinting* strokes and leaving artefacts in the colour of the holdout isn't expected behaviour?

Antonio Vazquez commented

2021-09-15 15:55:44 +02:00

Example:

2021-09-15 15-54-59.mp4

Example: [2021-09-15 15-54-59.mp4](https://archive.blender.org/developer/F10419718/2021-09-15_15-54-59.mp4)

Alasdair Beckett-King commented

2021-09-15 16:05:41 +02:00

Thanks for the reply, I appreciate the demo! I see what you mean that a solid black holdout works as expected with no tinting. But, shouldn't it also hide the stroke which is part of a different object, rather than being limited to the strokes that are part of the same object?

And if holdouts only affect strokes within the same object, why does it tint the stroke that is part of a different object?

Thanks for the reply, I appreciate the demo! I see what you mean that a solid black holdout works as expected with no tinting. But, shouldn't it also hide the stroke which is part of a different object, rather than being limited to the strokes that are part of the same object? And if holdouts only affect strokes within the same object, why does it tint the stroke that is part of a different object?

Antonio Vazquez commented

2021-09-15 16:13:38 +02:00

Holdout only affects the same object and I don't see that it is tinting the other object ... it's like you are looking through tinted glass.

2021-09-15 16-11-33.mp4

Holdout only affects the same object and I don't see that it is tinting the other object ... it's like you are looking through tinted glass. [2021-09-15 16-11-33.mp4](https://archive.blender.org/developer/F10419884/2021-09-15_16-11-33.mp4)

Alasdair Beckett-King commented

2021-09-15 16:21:33 +02:00

If it is acts like tinted glass, I can't understand why I get such wildly different effects depending on the background colour. It only looks somewhat correct against the grey background.

If it is acts like tinted glass, I can't understand why I get such wildly different effects depending on the background colour. It only looks somewhat correct against the grey background. ![image.png](https://archive.blender.org/developer/F10419894/image.png) ![image.png](https://archive.blender.org/developer/F10419896/image.png) ![image.png](https://archive.blender.org/developer/F10419898/image.png)

Philipp Oeser removed the

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Holdout Fill not working as expected with Grease Pencil #89879