How to Animate Curve Drawing in Blender with Bevel

Animating a procedural curve drawing effect in Blender is a straightforward technique commonly used for motion graphics, handwriting effects, and growing vines. By adjusting the curve's bevel depth and keyframing the Start and End mapping factors under the Object Data properties, you can precisely control how and when a curve appears along its path. This guide explains how to set up your curve geometry and configure these factors to create a seamless drawing animation.

Step 1: Add and Shape Your Curve

  1. In the 3D Viewport, press Shift + A and select Curve > Bézier (or Path / Nurbs Curve).
  2. Switch to Edit Mode (Tab) to shape, extrude (E), and position your curve as desired.
  3. Return to Object Mode (Tab).

Step 2: Add Bevel Geometry to the Curve

For the Start and End factors to be visible, the curve must have geometric thickness:

  1. Select the curve and open the Object Data Properties panel (the green curve icon on the right).
  2. Expand the Geometry section, then expand the Bevel sub-section.
  3. Set the Bevel Depth to a value greater than 0 (e.g., 0.05 m) to give the curve volume.
  4. (Optional) Increase the Resolution slider for a smoother, rounder profile.

Step 3: Configure Start and End Mapping Factors

Under the same Geometry tab, locate the Start & End Mapping (or Bevel Factor) section. Here you will find two primary sliders:

  • Factor Start: Controls the beginning point of the visible bevel along the curve (values range from 0.0 to 1.0).
  • Factor End: Controls the termination point of the visible bevel along the curve (values range from 0.0 to 1.0).

Step 4: Keyframe the Drawing Animation

To animate a standard "draw on" effect from start to finish:

  1. Move the timeline playhead to your starting frame (e.g., Frame 1).
  2. In the curve properties, set Factor End to 0.0.
  3. Hover your mouse over the Factor End field and press I (or click the dot next to the field) to insert a keyframe.
  4. Move the timeline playhead to your end frame (e.g., Frame 60).
  5. Set Factor End to 1.0.
  6. Hover over the Factor End field and press I to insert the second keyframe.

Step 5: Advanced Variations

Creating a Tracing or "Worm" Effect

To make a line segment travel along the path rather than just growing:

  1. Animate Factor End from 0.0 to 1.0.
  2. Offset the animation of Factor Start so it follows slightly behind Factor End (for example, keyframe Factor Start from 0.0 to 1.0 between Frame 15 and Frame 75).

Reversing the Drawing Direction

If the curve draws in the wrong direction:

  1. Enter Edit Mode (Tab).
  2. Select all control points (A).
  3. Go to the top viewport menu and choose Segment > Switch Direction.

Step 6: Adjust Timing in the Graph Editor

To change the pacing of the drawing effect:

  1. Open the Graph Editor or Dope Sheet workspace.
  2. Select your keyframes to modify the interpolation (press T to switch between Linear, Bézier, or other easing modes) to achieve the desired acceleration and deceleration for your animation.