CubicTo.cs

using System.Threading.Tasks;
using SkiaSharp;
 
namespace Waher.Layout.Layout2D.Model.Figures.SegmentNodes
{
    public class CubicTo : Point3, ISegment, IDirectedElement
    {
        public CubicTo(Layout2DDocument Document, ILayoutElement Parent)
            : base(Document, Parent)
        {
        }
 
        public override string LocalName => "CubicTo";
 
        public override ILayoutElement Create(Layout2DDocument Document, ILayoutElement Parent)
        {
            return new CubicTo(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);
                PathState.Set(this.xCoordinate3, this.yCoordinate3);
            }
        
            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);
                this.P3 = new SKPoint(this.xCoordinate3, this.yCoordinate3);
 
                PathState.Set(this.xCoordinate, this.yCoordinate);
                PathState.Set(this.xCoordinate2, this.yCoordinate2);
                PathState.Set(this.xCoordinate3, this.yCoordinate3);
                Path.CubicTo(this.P1, this.P2, this.P3);
            }
        
            return Task.CompletedTask;
        }
 
        protected SKPoint P0;
 
        protected SKPoint P1;
 
        protected SKPoint P2;
 
        protected SKPoint P3;
 
        public bool TryGetStart(out float X, out float Y, out float Direction)
        {
            // B(t) = (1-t)³P₀+3(1-t)²tP₁+3(1-t)t²P₂+t³P₃
            // B'(t) = 3(1-t)²(P₁-P₀)+6(1-t)t(P₂-P₁)+3t²(P₃-P₂)
            //
            // B'(0) = 3(P₁-P₀)
            // B'(1) = 3(P₃-P₂)
            //
            // Ratio will be compared, so no need to multiply with 3.
 
            float dx = P1.X - P0.X;
            float dy = 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 dx = P3.X - P2.X;
            float dy = P3.Y - P2.Y;
 
            X = this.P3.X;
            Y = this.P3.Y;
            Direction = CalcDirection(dx, dy);
 
            return this.defined;
        }
 
    }
}