Custom Brush Dynamic Angle Tracing in GIMP

Creating ribbon effects in GIMP requires linking the rotation angle of a flat or directional brush to the movement vector of your cursor or path. This tutorial provides a direct, step-by-step guide to creating a custom Paint Dynamic, mapping brush angle to stroke direction, smoothing the trajectory, and producing clean ribbon and calligraphic effects.

Step 1: Select a Directional Brush

A standard circular brush cannot create a ribbon effect because rotating a circle produces no visible difference.

  1. Select the Paintbrush Tool (P).
  2. Open the Brushes Dialog (Ctrl + Shift + B).
  3. Choose or generate an asymmetrical or flattened brush (such as a thin rectangle, a flat oval, or a custom slice shape).
  4. Set the brush aspect ratio high enough in the Tool Options (e.g., Aspect Ratio: 10.0 to 20.0) if using a standard parametric brush.

Step 2: Create a New Paint Dynamic

  1. Open the Paint Dynamics Dialog via Windows > Dockable Dialogs > Paint Dynamics.
  2. Click the Create New Dynamics button at the bottom of the dialog panel.
  3. Give your dynamic a name, such as Ribbon Dynamic.

Step 3: Configure the Dynamics Matrix

The Paint Dynamics Editor will open automatically showing a matrix of inputs (columns) and outputs (rows).

  1. Locate the Angle row.
  2. Check the box in the Direction column. This instructs GIMP to rotate the brush stamp based on the direction the cursor is moving.
  3. (Optional) If you are using a drawing tablet, you can check Size under Pressure to taper the ribbon stroke based on pen force.

Step 4: Adjust Tool Options for Smoothness

Direction-based rotation can jitter on small hand movements. To ensure clean lines:

  1. In the Tool Options dock, select your newly created Ribbon Dynamic from the Dynamics dropdown.
  2. Check the Smooth Stroke option.
  3. Increase the Weight (e.g., between 20 and 50) and Quality to stabilize mouse or stylus input, preventing sudden 180-degree flips in the brush angle.
  4. Adjust the base Angle slider in the Tool Options if the brush stroke runs perpendicular to the movement instead of parallel to it.

Step 5: Paint the Ribbon Effect

  1. Draw freehand curves onto your canvas; the brush will automatically align its rotation with the path of travel, generating a ribbon-like strip.
  2. To create mathematically perfect ribbons, draw a curve with the Paths Tool (B), navigate to Edit > Stroke Path, select Stroke with a paint tool, choose the Paintbrush, and check Emulate brush dynamics before applying.