Recommended test
Use a vertical centreline and a four-point freeform half-profile.
- Press M, click two vertically separated points, and confirm the purple guide says Active mirror.
- Press B and place four control points on one side. Confirm the purple reflected curve appears while drawing.
- Press Enter. Select the spline and drag a gold source handle; both sides should update together.
- Select the guide and drag either endpoint. Confirm the source stays fixed while the reflected side follows the new axis.
- Undo and redo each edit, then use the Spline Properties button to remove and restore a mirror relationship.
01 · CENTRELINE
Create and activate a mirror guide
Choose Mirror from the tool rail or press M. Click the first and second guide points. The dashed axis extends across the canvas, the finite guide span remains selectable, and the new guide becomes active automatically.
Select the guide to enter exact X1, Y1, X2, and Y2 coordinates. The Properties panel also reports its length and angle. Drag either endpoint for direct editing.
02 · DRAW
See symmetry before committing
With a guide active, start Spline with B. The editable source is gold while its derived reflection is purple. Every added control point updates both sides immediately. Finish or close the spline normally.
The purple curve is deliberately derived rather than stored as a second independent object. This prevents the two sides from drifting apart and keeps the document relationship explicit.
03 · REFINE
Change the source or the axis
Select the source spline and drag its gold control points. Select the guide and move its endpoints to change the centreline. Both interactions show the reflected result live and commit one undoable command when released.
The guide’s Properties button activates or deactivates it for newly drawn splines. Deactivation hides the centreline immediately, while existing linked splines retain their relationship. Select the guide from Objects to reveal it for editing or reactivation. A selected spline can remove its mirror or attach the currently active guide.
REFERENCE
Controls
IMPLEMENTATION NOTE
Associative document relationship
The guide and source spline are renderer-independent millimetre entities. The spline stores the guide identifier; reflected control points are recalculated for display rather than saved as duplicate geometry.
{
"kind": "mirror-guide",
"start": { "x": 100, "y": 20 },
"end": { "x": 100, "y": 260 }
}
{
“kind”: “spline”,
“mirrorGuideId”: “guide-id”,
“controlPoints”: [ … ]
}
CURRENT SCOPE
A mirrored closed loop can now drive CAM
- A half-spline whose endpoints meet the guide resolves as one checked closed contour
- Outside and Inside tool-radius compensation, curved tabs, direct start placement, 3D, animation, and guarded export are available
- Associative mirroring for lines, rectangles, circles, and arcs remains planned
- Converting the derived reflection into independent geometry remains planned
- Multiple reflected copies or rotational patterns remain planned
- Automatic tangent seam constraints remain planned; the user must shape the guide endpoints deliberately