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Icon Alpha property also affects the thumbnails of matcaps/studio lighting...
Confirmed, NormalPublicTO DO


System Information
Operating system: Win 10

Blender Version
Broken: blender-2.91.0-68797982025c-windows64
Worked: ?

Short description of error
The "Icon Alpha" property in the Themes settings also affects the thumbnails of stuff like matcaps/studio lights....

Exact steps for others to reproduce the error
Go to: Edit -> Preferences -> Themes -> User Interface -> Styles; now try to adjust the "Icon Alpha" property while the matcaps panel is open to see the effect...

Event Timeline

Philipp Oeser (lichtwerk) changed the task status from Needs Triage to Needs Information from User.Sep 2 2020, 12:02 PM

Well, these are icons, all preview icons are affected [material, ...].

Personally, I think the Icon Alpha property is a rare thing to tweak anyways (is this done in any theme we are shipping?), but to stay on topic: Do you mean these should be treated as thumbnails in the Filebrowser?
Pretty sure this would not be considered a bug, I am also not sure which of the preview icons one would want to exclude from being considered for Icon Alpha. (Like I said, if we do it for matcaps, we should do it for material preview icons as well).

@Hans Goudey (HooglyBoogly) : got an opinion here? Tempted to close as feature request to be honest...

Well, these are icons, all preview icons are affected [material, ...].

I don't think that's right. Those are (or technically should be) previews/thumbnails. Icons are meant to be iconic representation of certain thing, so accuracy is not so important there. Color correcting icons is fine. Previews or thumbnails on the other hand have purpose of giving you as close preview of the expected result as possible. Those spheres are there to give you as accurate representation of what your scene shading will look like after applying given matcap before you even click it, so that you can decide which one to use without several trial and error cycles.

I'd throw it into same category as for example file browser thumbnails. When you are browsing your texture library you want to see exactly how each texture looks without having to open it first. If you now have some sort of non opaque alpha, and you are previewing thumbnails on a very dark background, suddenly all textures seem darker than they should be, and you are not certain to what degree that's a product of the texture look itself, or the reduced opacity. So the only reasonable choice is to make Alpha 1.0 in such case, but that would then make having that alpha slider completely pointless, since tinting your icons with color of the UI background by reducing alpha would at the same time corrupt accuracy of thumbnails, a category which matcap previews fall into.

So I think on more abstract, UI system level, Blender should certainly differ which UI elements are meant to be icons (tool icons, panel icons, button icons, etc...) and which UI elements are meant to be thumbnails (file browser thumbnails, matcap thumbnails, HDRI thumbnails, texture thumbnails, etc...), and should exclude latter category from any degree of UI color correction.

I think we can just disable the alpha factor for previews, it doesn't make sense from what I can tell.
If there are reasons to have it, we could add a separate theme option. But icons and previews are indeed very different things on a user level.

Philipp Oeser (lichtwerk) changed the task status from Needs Information from User to Confirmed.Sep 2 2020, 12:41 PM
Philipp Oeser (lichtwerk) changed the subtype of this task from "Report" to "To Do".

Those are (or technically should be)

That would make the distinction between a bug and a request :)

But I totally agree with the reasoning, that is why I mentioned thumbnails in the filebrowser as well, it doesnt really make sense to act on the previews.
(it is not the only dark corner in blender that doesnt make sense, but still technically is not a bug though...)

I think we can just disable the alpha factor for previews

Reading that as marking it a TODO, feel free to change to anything else if needed.

Do we even need this option? This was for color icons ("to reduce contrast"), now the color of icons respects the theme settings.

Removing it would be fine with me. I also don't see a need and initially thought it was added during 2.8. But seems it's an old option and probably redundant by now.