Arcs
Creates a coordinated circular arc across two F-Curves, useful for converting separate horizontal and vertical motion into a smooth, physically plausible arc.
How it works
The Arcs tool works with two or three location F-Curves (X, Y, and/or Z), each with at least two selected keyframes. The operator creates a 3D parabolic arc between the first and last selected keyframes on each curve, using the specified vertical axis to determine the arc direction. Any keyframes between the first and last selected keyframes will be handled automatically to follow the arc path.
Redo Panel
After running the operator, use the Redo panel to tweak the arc geometry, timing and easing factors.
Properties
| Property | Type | Default | Description |
|---|---|---|---|
| Arc Height | Number | 0.5 | Height of the arc measured along the selected vertical axis. Positive values create arcs in the positive axis direction; negative values in the negative direction. |
| Ease In Factor | Number | 0.5 | Controls easing at the start of the arc (0: linear, 1: maximum slow-in). |
| Ease Out Factor | Number | 0.5 | Controls easing at the end of the arc (0: linear, 1: maximum slow-out). |
| Vertical Axis | Dropdown | Z | Axis along which the arc height is applied (X, Y, or Z). |
| Ease Type | Dropdown | TIMING_ALIGNED | Method used to achieve easing: TIMING_ALIGNED (best arc with Bezier handles) or FLAT_HANDLES (mid-key with slow out/in). |
Arc Height
Controls the height of the parabolic arc measured along the selected vertical axis. Positive values create arcs in the positive direction of that axis, negative values in the negative direction. A value of 0 creates a straight line between keyframes.
Ease In / Ease Out
Adjusts timing ease applied to the arc endpoints. Higher values increase the slow-in or slow-out portion of the motion. These factors affect how the Bezier handles are positioned in time to create the desired easing.
Vertical Axis
Determines which global axis the arc height is applied along. Choose X, Y, or Z depending on your scene orientation and the desired arc direction. For example, if Z is up in your scene, select Z to create upward/downward arcs.
Ease Type
Timing Aligned (Best Arc): Creates a smooth arc using a single curve segment with FREE Bezier handles. The handles are positioned along the arc path to control both timing and curvature, resulting in the most accurate parabolic motion. This is the recommended mode for most arc animations.
Flat Handles (Mid-Key Slow Out/In): Inserts a midpoint keyframe at the arc peak with AUTO handles, creating a more traditional slow-out/slow-in animation. The start and end keyframes receive flat handles perpendicular to the motion direction. This mode is useful when you want a pronounced peak with distinct easing phases.
Quick Steps
- Select two or three location F-Curves (X, Y, and/or Z) with at least two keyframes selected on each curve. The first and last selected keyframes define the arc endpoints.
- Run the 3D Arcs operator from the Graph Editor menu or search (F3).
- Choose Vertical Axis to determine the direction of the arc (typically Z for up/down arcs).
- Adjust Arc Height to control the arc curvature, and set Ease In/Out values for timing control.
- Select Ease Type: use Timing Aligned for smooth arcs, or Flat Handles for more pronounced slow-out/in motion.
- Use the Redo Panel to fine-tune the result. Your original keyframe selection will be preserved for further adjustments.
Use Cases
Timing Aligned: Best for creating smooth, physically accurate arcs in 3D space. The operator calculates precise Bezier handle positions that follow the parabolic arc path, ensuring both the timing and spatial curve are correct. This mode doesn’t add extra keyframes, keeping your animation curves clean.
Flat Handles: Ideal when you want a more pronounced peak with traditional animation timing. The operator inserts a midpoint keyframe at the arc’s highest point and creates flat handles on the start and end keys, giving you classic slow-out/slow-in motion that’s easy to adjust further.
Common Pitfalls
- Wrong axis selection: If your arc appears flat or goes in the wrong direction, check that the Vertical Axis matches your scene’s up direction.
- Mismatched keyframe timing: All selected F-Curves must have their first selected keyframe on the same frame, and their last selected keyframe on the same frame. If they don’t match, the operator will show an error message.
- Non-location F-Curves: The operator only works with location F-Curves (X, Y, Z position). Rotation or scale curves are automatically filtered out.
- Zero-length time span: The first and last selected keyframes must be on different frames to compute timing and arc motion.
For more details, refer to the operator’s redo panel after running it, or check the inline documentation in the add-on source code.