A radial shading (Type 3): colour varies between two circles, through the blend circles between them.
public sealed class PdfRadialShading : PdfShading
ISO 32000-2 §8.7.4.5.4, Table 80. The blend circle for s in [0, 1] has centre (x₀ + s(x₁ − x₀), y₀ + s(y₁ − y₀)) and radius r₀ + s(r₁ − r₀); an extended end continues it below 0 or above 1 while the radius is not negative. Circles are painted in order of increasing s, so a point on several of them takes the colour of the greatest s (§8.7.4.5.4: "the last of the enclosing circles to be painted"). TryGetParameter(Double, Double, out Double) computes that s and the t it maps to.
Repairs: a negative radius reads as 0, with a diagnostic. Both radii 0 paint nothing.
kind:method, kind:property, kind:ctor. Press Esc to clear.DomainGets [t₀ t₁], the parametric values at the starting and ending circles. Default [0 1].EndCenterGets the centre of the ending circle, (x₁, y₁), in the target space.EndRadiusGets the radius of the ending circle, r₁, never negative.ExtendEndGets a value indicating whether the shading extends beyond the ending circle. Default false.ExtendStartGets a value indicating whether the shading extends beyond the starting circle. Default false.StartCenterGets the centre of the starting circle, (x₀, y₀), in the target space.StartRadiusGets the radius of the starting circle, r₀, never negative.TryGetParameter(Double, Double, out Double)Returns the parametric value t of a point of the target space: the greatest s whose blend circle passes through it.