1. Home
  2. Docs
  3. Concepts
  4. Library Architecture

Library Architecture

Spline is structured around a small set of geometry responsibilities that can be reused without any Avalonia dependency.

Core building blocks

  • Vec2 provides the package's basic 2D vector type.
  • MathUtils and Polynomial support low-level numerical operations.
  • CubicBezier and TwoCubics model Bezier control geometry and segment transformations.
  • BezierPath represents rendered output as commands and also supports distance-based hit testing.
  • Spline, TwoParamCurve, MyCurve, and TwoParamSpline form the existing curvature-oriented fair-spline solving and rendering pipeline.
  • GlobalBSpline is the CAD-oriented interpolation layer. It converts fit points plus endpoint tangents into an explicit cubic B-spline control net in O(n) time.
  • BSplineCurve is the canonical non-rational B-spline geometry layer. It owns degree, control points, knots, unit weights, de Boor evaluation, derivatives, and exact cubic Bezier conversion.
  • CurveGrid stores an interpolated grid of curve masters for the tuner workflow.
  • PolylineUtils provides headless simplification and resampling utilities for converting traced input into spline control points.

Two independent spline contracts

The fair-spline and CAD B-spline subsystems intentionally share low-level geometry but not their solver state:

Spline.CP[]
    -> Spline / TwoParamSpline
    -> tangent + curvature solve
    -> BezierPath

fit Vec2[] + endpoint tangents
    -> GlobalBSpline
    -> BSplineCurve { degree, control points, knots, weights }
    -> de Boor evaluation or exact BezierPath conversion

This avoids forcing the existing fair-spline solver into B-spline semantics and avoids reducing CAD geometry to a rendering-only Bezier chain.

Separation of concerns

The package intentionally excludes:

  • windowing and view logic
  • app settings persistence
  • input handling and editing UX
  • file-picker and rendering-surface integration
  • product-specific CAD parsers and serializers

Those responsibilities stay in host applications. samples/DemoSpline is the interactive fair-spline host, while samples/GlobalBSplineSample is a focused headless example of the CAD-oriented API.

Typical fair-spline consumer flow

  1. create Spline.CP interpolation points
  2. construct a Spline
  3. call Solve()
  4. optionally call ComputeCurvatureBlending()
  5. render via Render() or RenderSvg()

Typical CAD B-spline consumer flow

  1. collect fit points and endpoint tangents
  2. call GlobalBSpline.Interpolate or InterpolateDetailed
  3. preserve Degree, ControlPoints, Knots, and Weights for CAD geometry
  4. evaluate with BSplineCurve.Evaluate() or EvaluateDerivative()
  5. convert to BezierPath/SVG only at the rendering boundary when needed