Smears added with the Smudge Pencil

Under the hood

Smudge Pencil combines Blender Studio's Brushstroke Tools and a modified refraction shader from Dillon Goo's Mesh Trails Add-on. The shader was tweaked to work in camera view and follow stroke direction. I streamlined the Brushstroke Tools for smudging and added features to prevent overlapping strokes, which would break the refraction rendering.

The rig used in the example files can be found here.

Limitations

‼️ Smudge Pencil relies on refraction, so it doesn’t smudge Grease Pencil lines directly.

💡 Solution: Convert Grease Pencil lines into geometry using Brushstroke Tools OR smudge a rendered image sequence/video (example file included).

‼️ For scenes with foreground, middle-ground, and background, smudging requires Cycles rendering. Separate the animation into ViewLayers and composite them using "Alpha Over" nodes (example file included).

Smudge Pencil...

... is a Grease Pencil object with a Geometry Nodes setup which

1. generates geometry lines from the Grease Pencil lines
2. and assigns a refraction shader that smudges the objects behind the lines according to the Grease Pencil lines' size, strength, and direction.

Also, the Grease Pencil object is constrained to the camera for easy smudging.

Why did I create this

I'm the director of a short called Sierra. In the film, I used Krita's smudge brush to create smears on fast movements. I was honestly baffled when I found this method in Blender.

What's included

● Smudge Pencil Object w/ Geometry Nodes Setup

● 2 Example Scenes

• Simple Smudge Scene with an image plane for optimized smudging. EEVEE and Cycles.
• Scene w/ a compositing setup separating smudges in foreground, middle-ground, and background. Cycles only. (EEVEE doesn't support Alpha in Refractions.)

● 7 Adjustable Brushes & Effects

● Future Updates

Install

1. Copy the "SmudgePencil Asset" folder to a folder where you keep your assets (for example: /Documents/Blender/SmudgePencil Asset/)
2. In Blender, add the folder to: Preferences > File Paths > Asset Libraries > [+]
3. Set the Import Method: Append

Getting Started

1. Open the Asset Browser
2. Drag & Drop the SmudgePencil asset to your scene
3. Set the Camera in the Constraints tab
4. Adjust the Distance from Camera
5. Switch to Active Camera View, and Draw Mode, and make the brush radius a bit bigger
6. SMUDGE!
7. Adjust the Settings in the Modifiers tab
8. (EEVEE) Activate Raytracing in Render Settings

System Requirements, Compatibility & EEVEE limitations

• A computer with a decent GPU
• Blender 4.3+ (Windows, MacOS, Linux)
• EEVEE* & Cycles

*EEVEE is limited to only 1 layer of refractions, so you can't smudge a smudge.

*EEVEE doesn't support alpha in refractions. A workaround could be keying out a bright-colored background.

Required User Skills

I set up the nodes with beginners in mind. Still, a certain degree of understanding of Geometry Nodes and Shaders will be useful. If it's your first time opening Geometry Nodes, this could be an exciting dive into the nodes! Tweaking and switching up the connections and node types is part of the fun and lets you invent your style for the smudges.

Feedback & Help

Feel free to reach out to me at sander.joon@gmail.com for any suggestions, questions, or assistance with the setup. I’d be happy to help! 🤗