Solver and Curvature

The Spline type works from control points that are marked as either corner or smooth. Each point can optionally carry explicit left or right tangent angles.

Solve phase

Spline.Solve() walks the control-point list segment by segment.

Straight corner-to-corner spans without explicit tangents fall back to the chord direction directly.
Smooth spans are grouped and solved through TwoParamSpline.
TwoParamSpline.InitialThs() seeds tangent angles from neighboring chord directions.
TwoParamSpline.IterDumb() refines those angles iteratively so adjacent segment curvatures stay coherent.

The result of Solve() is a set of computed left and right tangent angles on the working control points.

Curvature blending

Spline.ComputeCurvatureBlending() adds a second pass for smooth joints.

It recomputes curvature at the right end of the previous segment and the left end of the next segment.
When both sides have compatible curvature sign, it blends them harmonically.
When the signs disagree, the blend is forced to zero.

The blended curvature values are later used to choose between a raw cubic shape and a curvature-adjusted quintic shape.

Rendering modes

Raw cubic mode uses MyCurve.Render() and preserves the baseline two-control representation.
Curvature-adjusted mode uses MyCurve.Render4() and inserts additional control points derived from Hermite-based curvature correction.