Paint Mode: Erasing #98590

New Issue

Julien Kaspar · 2022-06-04T16:36:53+02:00

Julien Kaspar commented

2022-06-04 16:36:53 +02:00

NOTE: This task is currently to document the requirements for erasing workflows for painting. This should be the basis for discussions on the implementation.

Goal

For an intuitive painting workflow it's necessary to have an eraser accessible at all times.
This has been a shortcoming in Blender for painting, since the erasing of alpha channels has only been available as a blending mode for brushes.
This is very hard to access via the UI and shortcuts.

Recommendations

The ideal solution is to have a very simple brush tool in the toolbar. Aside from the typical texture, stroke, falloff and cursor settings, it can only erase alpha.

This tool can then have the shortcut E assigned by default to make it very accessible.

Pure Emissive Colors

The motivation behind not offering a blending mode to "Add Alpha" in the Erase Tool is because this has been notoriously difficult to do like the user would expect.
See #86868 & #83342.

When painting float or pre-multiplied images, the alpha is treated differently. Any color with an alpha 0 would have the RGB colors displayed as pure emissive colors and still visible.
The only way to erase the colors completely is to also erase the RGB channels to 0.

As a result the design for the brush should emphasise this: The Erase brush is a destructive tool!
If you erase the alpha directly via painting tools you should expect to likely lose the full RGBA color information.
The alpha 0 areas can be painted over with a new color afterwards.

For non destructive erasing of alpha values it is recommended to use a separate image as a mask. This can be done right now via nodes.
This non-destructive approach might not be very accessible right now but that can be addressed separately (Especially with the layered textures design)

Erasing Selections

We need to discuss how we want to handle other erasing operations like via Gesture Tools (Box/Lasso/Line Erase), or for example the Color Filter for gradual erasing. These generally affect the unmasked/selected areas.
There are different ways to enable this workflow.

Erase Operator

The simplest way would be to add an operator to the menus and mapped to a shortcut (Like Delete) to erase the colors on any selected areas.
The user would in that case use the existing Gesture Tools and brushes to mask/select areas to define the areas to be deleted.
This approach would follow the Select -> Operate paradigm of Blender closest.

Erase Tools

The existing Color Filter tool could receive an additional Filter Type to 'Erase'. This would allow gradual erasing in the case where it is needed.
Adding Gesture Tools specifically or erasing is also possible but might just bloat the Toolbar.

Erase Mode

An alternative approach is to make the "Erase Alpha" blending mode in the regular painting tools more accessible.
In other painting application such as Krita every tools and brush has an "Erase Mode" button that can be easily toggled with a shortcut and applies globally to all tools and brushes.
We could implement this design as an alternative to the Erase Tools/Brush for users that prefer this workflow.

In that case the Erase Alpha blending mode would be a button in the header that can be toggled directly, instead of being part of the blending modes popup.
A shortcut could also be assigned.
This toggle should be available for for all brushes and tools that affect colors.

NOTE: This task is currently to document the requirements for erasing workflows for painting. This should be the basis for discussions on the implementation. # Goal For an intuitive painting workflow it's necessary to have an eraser accessible at all times. This has been a shortcoming in Blender for painting, since the erasing of alpha channels has only been available as a blending mode for brushes. This is very hard to access via the UI and shortcuts. # Recommendations The ideal solution is to have a very simple brush tool in the toolbar. Aside from the typical texture, stroke, falloff and cursor settings, it can only erase alpha. This tool can then have the shortcut `E` assigned by default to make it very accessible. ## Pure Emissive Colors The motivation behind not offering a blending mode to "Add Alpha" in the Erase Tool is because this has been notoriously difficult to do like the user would expect. See #86868 & #83342. When painting float or pre-multiplied images, the alpha is treated differently. Any color with an alpha 0 would have the RGB colors displayed as pure emissive colors and still visible. The only way to erase the colors completely is to also erase the RGB channels to 0. As a result the design for the brush should emphasise this: **The Erase brush is a destructive tool!** If you erase the alpha directly via painting tools you should expect to likely lose the full RGBA color information. The alpha 0 areas can be painted over with a new color afterwards. For non destructive erasing of alpha values it is recommended to use a separate image as a mask. This can be done right now via nodes. This non-destructive approach might not be very accessible right now but that can be addressed separately (Especially with the [layered textures design](https://code.blender.org/2022/02/layered-textures-design/)) ## Erasing Selections We need to discuss how we want to handle other erasing operations like via Gesture Tools (Box/Lasso/Line Erase), or for example the Color Filter for gradual erasing. These generally affect the unmasked/selected areas. There are different ways to enable this workflow. **Erase Operator** The simplest way would be to add an operator to the menus and mapped to a shortcut (Like `Delete`) to erase the colors on any selected areas. The user would in that case use the existing Gesture Tools and brushes to mask/select areas to define the areas to be deleted. This approach would follow the Select -> Operate paradigm of Blender closest. **Erase Tools** The existing Color Filter tool could receive an additional Filter Type to 'Erase'. This would allow gradual erasing in the case where it is needed. Adding Gesture Tools specifically or erasing is also possible but might just bloat the Toolbar. ## Erase Mode An alternative approach is to make the "Erase Alpha" blending mode in the regular painting tools more accessible. In other painting application such as Krita every tools and brush has an "Erase Mode" button that can be easily toggled with a shortcut and applies globally to all tools and brushes. We could implement this design as an alternative to the Erase Tools/Brush for users that prefer this workflow. In that case the Erase Alpha blending mode would be a button in the header that can be toggled directly, instead of being part of the blending modes popup. A shortcut could also be assigned. This toggle should be available for for all brushes and tools that affect colors.

Julien Kaspar commented

2022-06-04 16:36:53 +02:00

Added subscribers: @JulienKaspar, @JosephEagar, @Jeroen-Bakker, @jfmatheu

Julien Kaspar commented

2022-06-09 10:37:09 +02:00

From the recent module meeting:

But we need to be aware of use cases to still add/remove alpha. For gamedev the alpha channel is often used for other purposes than transparency.

One possible fix: We can prevent destructive erasing by changing the behaviour directly in the color mixing of brushes & tools. This would prevent erasing the RGB values on color attributes and most image types (Including newly created images that aren’t saved yet).
When erasing on pre-multiplied images on the other hand, we could still allow erasing alpha channel in an expected way within Blender. Afterwards when saving the file it would cause data loss that should’ve happened already while erasing.
Here we must show a warning message to the user, which gives them the chance to save to another image format or ways to export before saving.

We'll discuss further how well we can preserve the Alpha channel while erasing.

From the [recent module meeting](https://devtalk.blender.org/t/2022-6-8-sculpt-texture-paint-module-meeting/24672): > But we need to be aware of use cases to still add/remove alpha. For gamedev the alpha channel is often used for other purposes than transparency. > > One possible fix: We can prevent destructive erasing by changing the behaviour directly in the color mixing of brushes & tools. This would prevent erasing the RGB values on color attributes and most image types (Including newly created images that aren’t saved yet). > When erasing on pre-multiplied images on the other hand, we could still allow erasing alpha channel in an expected way within Blender. Afterwards when saving the file it would cause data loss that should’ve happened already while erasing. > Here we must show a warning message to the user, which gives them the chance to save to another image format or ways to export before saving. We'll discuss further how well we can preserve the Alpha channel while erasing.

Evan Wilson commented

2022-06-10 05:43:59 +02:00

Added subscriber: @EAW

Julien Kaspar changed title from ~~Paint Mode: Eraser Tool~~ to Paint Mode: Erasing

2022-09-01 10:01:14 +02:00

Julien Kaspar added this to the Sculpt, Paint & Texture project 2023-02-08 10:20:48 +01:00

Philipp Oeser removed the

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Paint Mode: Erasing #98590

Goal

Recommendations

Pure Emissive Colors

Erasing Selections

Erase Mode