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UV Image Paint Bugs: Smear Tool Black Alpha and Radius Global Hotkey Broken
Open, Confirmed, MediumPublic


System Information
OS: Windows 8.1 64 bit
GPU: GTX 970

Blender Version
Broken: (2.78a Hash: e8299c8)
Worked: (issue has existed for awhile)

Short description of error

Hello, I thought I should report some bugs that have become quite prevalent now that I'm doing more texture painting in Blender.

  1. The first bug is with the Smear tool, which, when used in the UV Image Paint editor, results in solid black smearing on an image with an alpha channel IF any portion of the brush radius is touching the transparent alpha region when a stroke is made. (The black is the result of the base color of the image before 0 % alpha is selected. If your base color was white, then it will smear solid white in, etc.) This is illustrated in the attached photo: the bottom 3 strokes were made with the smear tool fully within the opaque pixels. The top 2 strokes were made with part of the brush overlapping into the alpha region, and the solid black result is visible.

As you can see in the image below, smear strokes made from within the 3D viewport appear "correct", whether blending out into an alpha region or whether blending in from one. The 2 bottom strokes were made in the UV Image Paint Editor and you can see the difference.

However, something is still off with the way alpha is handled, even in the 3D viewport, as dark edging is clearly visible at the borders of the alpha. This resembles exactly what a premultiplied alpha image looks like when incorrectly set to straight, but it makes no difference switching between Straight or Premultiplied alpha in the image preferences within Blender.

Also, this incorrect darkened edge will be baked into the final texture if Blender is used for texture baking, however, if you export all your individual paint layers and composite in GIMP for example, the alpha will display correctly.

  1. The final bug is with the UV Image Paint Editor not respecting the Global Hotkey setting for brush radius when I have the "F" key assigned to something else. I like to keep all transport controls at one hand, which is extremely useful for animation, hence I have Play/Pause = Spacebar; F = Step forward; D = Step backward; Q = Jump to start; E = Jump to end.

This all works perfectly fine in the 3D viewport even when Texture Painting, with the "F" key correctly adjusting brush size when the mouse focus is in the 3D viewport, and the "F" key correctly stepping forward 1 frame when the mouse focus is the Timeline. Unfortunately, the same cannot be said when the mouse focus is the UV image editor, resulting in the "F" key stepping playback forward rather than adjusting brush size.

It would be so fantastic to overcome these limitations, helping to make Texture Painting workflows in Blender even better. :-)

Thank you so much for your time in looking into this!

Adam Janz



Event Timeline

Aaron Carlisle (Blendify) triaged this task as Needs Information from User priority.

Please upload a simple test file that demonstrates this issue.

Hi Aaron,

Thanks so much for your response. I've uploaded a test file you can use to see the issue, as well as a link to an accompanying video showing the problem in realtime.

Thanks for looking into this!


Thank you, I will look at it later.

Joey Ferwerda (TheOnlyJoey) raised the priority of this task from Needs Information from User to Needs Triage by Developer.Feb 9 2017, 4:33 PM

Thanks guys! Don't forget to check the link to the video example. It shows pretty clearly how the different bugs react. My apologies for becoming braindead momentarily in the video when switching between bug subjects, LOL, that was my first-ever screen recording.


Dalai Felinto (dfelinto) triaged this task as Confirmed, Medium priority.

Thanks for the file. It's not ideal to report multiple issues in the same report, but I can confirm the (first) bug.

@Campbell Barton (campbellbarton) could you take a look at this? It's really easy to reproduce, just drag from outside the opaque area into the opaque area.

You're welcome. Thanks for looking into this. I'll remember to break issues up next time.

The 2D paint smear issue was solved in rB0d4fd7528f9b: Fix T46560: 2D paint smear and soften brushes not working with alpha..

The F key behaving different in the 3D view is due to rB9a7099f42830: Fix #19834: text edit mode left/right was not work due to frame prev/next.. In all editors except Text and 3D View the Frames keymap takes precedence over others. We could changing the Frames keymap (and maybe others) to have lower precedence in all editors, but changing this for 2.79 still is too risky and might break unknown use cases.

Thanks so much, Brecht, for the update! That's great to hear the smear tool has been fixed. As far as the F key is concerned, I have created 2 different keymaps and switch between them depending on whether painting or animating (this is a pretty handy work-around for the present).

Thank you for all your excellent work in developing Blender!