B-spline / NURBS

Edit an open clamped uniform B-spline/NURBS with two to eight control points. The curve appears immediately; valid degree, coordinate and weight edits redraw it directly. Drag a numbered handle with mouse, pen or touch. Click empty drawing space with a mouse to append a point; empty touch space scrolls the page. Points contains the selector, exact coordinates, weight and Remove. At least two points must remain. Pointer cancellation restores the original handle.

Degree is an integer from 1 to point count minus 1, at most 7. Coordinates are bounded to ±2 and positive weights to 0.05…5. Equal weights give a B-spline; increasing a weight pulls the rational curve toward its point. The first and last points are interpolated. Removing a point never silently lowers the degree: adjust an invalid degree explicitly. An invalid draft clears the curve and disables PNG until corrected.

Quarter circle loads (1,0), (1,1), (0,1) with weights 1,√½,1 and degree 2. This is mathematically a circular arc; the drawing approximates it with 512 segments. Reset restores five initial points and degree 3. Resizing fits the points uniformly without stretching the geometry. This is a small planar editor, not a CAD system or arbitrary knot editor.

The knot vector is available in Points. Basis values are iterative and weights normalized over active support. Calculations use floating point. PNG exports the current drawing with its input parameters embedded as metadata. Only raw degree, selected point and point coordinates/weights persist, including unfinished edits; curves are recalculated on reload, no saved image or view.