ConicTo.cs

using System.Threading.Tasks;
using SkiaSharp;
 
namespace Waher.Layout.Layout2D.Model.Figures.SegmentNodes
{
    public class ConicTo : Point2Weight, ISegment, IDirectedElement
    {
        public ConicTo(Layout2DDocument Document, ILayoutElement Parent)
            : base(Document, Parent)
        {
        }
 
        public override string LocalName => "ConicTo";
 
        public override ILayoutElement Create(Layout2DDocument Document, ILayoutElement Parent)
        {
            return new ConicTo(Document, Parent);
        }
 
        public virtual Task Measure(DrawingState State, PathState PathState)
        {
            if (this.defined)
            {
                PathState.Set(this.xCoordinate, this.yCoordinate);
                PathState.Set(this.xCoordinate2, this.yCoordinate2);
            }
    
            return Task.CompletedTask;
        }
 
        public virtual Task Draw(DrawingState State, PathState PathState, SKPath Path)
        {
            if (this.defined)
            {
                this.P0 = Path.LastPoint;
                this.P1 = new SKPoint(this.xCoordinate, this.yCoordinate);
                this.P2 = new SKPoint(this.xCoordinate2, this.yCoordinate2);
 
                PathState.Set(this.xCoordinate, this.yCoordinate);
                PathState.Set(this.xCoordinate2, this.yCoordinate2);
                Path.ConicTo(this.P1, this.P2, this.weight);
            }
        
            return Task.CompletedTask;
        }
 
        protected SKPoint P0;
 
        protected SKPoint P1;
 
        protected SKPoint P2;
 
        public bool TryGetStart(out float X, out float Y, out float Direction)
        {
            // P(t) = ((1 – t)²P₀ + 2wt(1 – t)P₁ + t²P₂) / ((1 – t)² + 2wt(1 – t) + t²)
            //      = ((1-2t+t²)P₀ + (2wt-2wt²)P₁ + t²P₂) / (1-2t+t²+2wt-2wt²+t²)
            //      = (P₀ +t(2wP₁-2P₀) + t²(P₀-2wP₁+P₂)) / (1+t(2w-2)+t²(2-2w))
            // 
            // P'(t) = ((2wP₁-2P₀+2t(P₀-2wP₁+P₂))*(1+t(2w-2)+t²(2-2w))-(P₀ +t(2wP₁-2P₀) + t²(P₀-2wP₁+P₂))*(2w-2+2t(2-2w)))/(1+t(2w-2)+t²(2-2w))²
            //
            // P'(0) = 2w(P₁-P₀)
            // P'(1) = -P₀-2wP₁+2P₂ = 2(P₂-wP₁)-P₀  Note: Error somewhere. Should be 2w(P₂-P₁) for symmetry
 
            float w2 = this.weight * 2;
            float dx = w2 * (P1.X - P0.X);
            float dy = w2 * (P1.Y - P0.Y);
 
            X = this.P0.X;
            Y = this.P0.Y;
            Direction = CalcDirection(dx, dy);
 
            return this.defined;
        }
 
        public bool TryGetEnd(out float X, out float Y, out float Direction)
        {
            float w2 = this.weight * 2;
            float dx = w2 * (P2.X - P1.X);
            float dy = w2 * (P2.Y - P1.Y);
 
            X = this.P2.X;
            Y = this.P2.Y;
            Direction = CalcDirection(dx, dy);
 
            return this.defined;
        }
    }
}