LanMountainDesktop/ThirdParty/DotNetCampus.InkCanvas/src/DotNetCampus.InkCanvas.SkiaInk/SkiaSimpleInkRender.cs

using DotNetCampus.Inking.Primitive;

using SkiaSharp;

using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;
using System.Text;
using System.Threading.Tasks;

namespace DotNetCampus.Inking;

/// <summary>
/// 特别简单的笔迹渲染器。
/// </summary>
internal class SkiaSimpleInkRender
{
    private static readonly Matrix3x2 RotationPiDiv8 = Matrix3x2.CreateRotation(MathF.PI / 8);
    private static readonly Matrix3x2 RotationPiDiv4 = Matrix3x2.CreateRotation(MathF.PI / 4);
    private static readonly Matrix3x2 Rotation3PiDiv8 = Matrix3x2.CreateRotation(3 * MathF.PI / 8);

    public SKPoint[] GetOutlineSKPointList(IReadOnlyList<InkStylusPoint> pointList, double inkSize)
    {
        if (pointList.Count < 2)
        {
            throw new ArgumentException("小于两个点的无法应用算法");
        }

        var outlinePointList1 = _outlinePointList1;
        var outlinePointList2 = _outlinePointList2;

        outlinePointList1.Clear();
        outlinePointList2.Clear();

        outlinePointList1.EnsureCapacity(pointList.Count * 2);
        outlinePointList2.EnsureCapacity(pointList.Count * 2);

        for (var i = 0; i < pointList.Count; i++)
        {
            // 笔迹粗细的一半，一边用一半，合起来就是笔迹粗细了
            var halfThickness = (float) inkSize / 2;

            // 压感这里是直接乘法而已
            halfThickness *= pointList[i].Pressure;
            // 不能让笔迹粗细太小
            halfThickness = MathF.Max(0.01f, halfThickness);

            if (i == 0 || pointList[i].Point == pointList[i - 1].Point)
            {
                if (i == pointList.Count - 1 || pointList[i].Point == pointList[i + 1].Point)
                {
                    continue;
                }

                var direction = Vector2.Multiply(halfThickness, Vector2.Normalize(new Vector2((float) pointList[i + 1].Point.X - (float) pointList[i].Point.X, (float) pointList[i + 1].Point.Y - (float) pointList[i].Point.Y)));

                var point1 = new SKPoint((float) (pointList[i].Point.X - direction.Y), (float) (pointList[i].Point.Y + direction.X));
                var point2 = new SKPoint((float) (pointList[i].Point.X + direction.Y), (float) (pointList[i].Point.Y - direction.X));

                if (i == 0)
                {
                    var direction0 = -direction;
                    var direction1 = Vector2.Transform(direction0, RotationPiDiv8);
                    var direction2 = Vector2.Transform(direction0, RotationPiDiv4);
                    var direction3 = Vector2.Transform(direction0, Rotation3PiDiv8);
                    var directionN1 = new Vector2(direction3.Y, -direction3.X);
                    var directionN2 = new Vector2(direction2.Y, -direction2.X);
                    var directionN3 = new Vector2(direction1.Y, -direction1.X);

                    outlinePointList1.Add(new SKPoint((float) (pointList[i].Point.X + direction0.X), (float) (pointList[i].Point.Y + direction0.Y)));
                    outlinePointList1.Add(new SKPoint((float) (pointList[i].Point.X + directionN1.X), (float) (pointList[i].Point.Y + directionN1.Y)));
                    outlinePointList1.Add(new SKPoint((float) (pointList[i].Point.X + directionN2.X), (float) (pointList[i].Point.Y + directionN2.Y)));
                    outlinePointList1.Add(new SKPoint((float) (pointList[i].Point.X + directionN3.X), (float) (pointList[i].Point.Y + directionN3.Y)));

                    outlinePointList2.Add(new SKPoint((float) (pointList[i].Point.X + direction0.X), (float) (pointList[i].Point.Y + direction0.Y)));
                    outlinePointList2.Add(new SKPoint((float) (pointList[i].Point.X + direction1.X), (float) (pointList[i].Point.Y + direction1.Y)));
                    outlinePointList2.Add(new SKPoint((float) (pointList[i].Point.X + direction2.X), (float) (pointList[i].Point.Y + direction2.Y)));
                    outlinePointList2.Add(new SKPoint((float) (pointList[i].Point.X + direction3.X), (float) (pointList[i].Point.Y + direction3.Y)));
                }

                outlinePointList1.Add(point1);
                outlinePointList2.Add(point2);
            }
            else if (i == pointList.Count - 1 || pointList[i].Point == pointList[i + 1].Point)
            {
                var direction = Vector2.Multiply(halfThickness, Vector2.Normalize(new Vector2((float) pointList[i].Point.X - (float) pointList[i - 1].Point.X, (float) pointList[i].Point.Y - (float) pointList[i - 1].Point.Y)));

                var point1 = new SKPoint((float) (pointList[i].Point.X - direction.Y), (float) (pointList[i].Point.Y + direction.X));
                var point2 = new SKPoint((float) (pointList[i].Point.X + direction.Y), (float) (pointList[i].Point.Y - direction.X));

                outlinePointList1.Add(point1);
                outlinePointList2.Add(point2);

                if (i == pointList.Count - 1)
                {
                    var rotationPiDiv8 = Matrix3x2.CreateRotation(MathF.PI / 8);
                    var rotationPiDiv4 = Matrix3x2.CreateRotation(MathF.PI / 4);
                    var rotation3PiDiv8 = Matrix3x2.CreateRotation(3 * MathF.PI / 8);

                    var direction0 = direction;
                    var direction1 = Vector2.Transform(direction0, rotationPiDiv8);
                    var direction2 = Vector2.Transform(direction0, rotationPiDiv4);
                    var direction3 = Vector2.Transform(direction0, rotation3PiDiv8);
                    var directionN1 = new Vector2(direction3.Y, -direction3.X);
                    var directionN2 = new Vector2(direction2.Y, -direction2.X);
                    var directionN3 = new Vector2(direction1.Y, -direction1.X);

                    outlinePointList1.Add(new SKPoint((float) (pointList[i].Point.X + direction3.X), (float) (pointList[i].Point.Y + direction3.Y)));
                    outlinePointList1.Add(new SKPoint((float) (pointList[i].Point.X + direction2.X), (float) (pointList[i].Point.Y + direction2.Y)));
                    outlinePointList1.Add(new SKPoint((float) (pointList[i].Point.X + direction1.X), (float) (pointList[i].Point.Y + direction1.Y)));
                    outlinePointList1.Add(new SKPoint((float) (pointList[i].Point.X + direction0.X), (float) (pointList[i].Point.Y + direction0.Y)));

                    outlinePointList2.Add(new SKPoint((float) (pointList[i].Point.X + directionN3.X), (float) (pointList[i].Point.Y + directionN3.Y)));
                    outlinePointList2.Add(new SKPoint((float) (pointList[i].Point.X + directionN2.X), (float) (pointList[i].Point.Y + directionN2.Y)));
                    outlinePointList2.Add(new SKPoint((float) (pointList[i].Point.X + directionN1.X), (float) (pointList[i].Point.Y + directionN1.Y)));
                    outlinePointList2.Add(new SKPoint((float) (pointList[i].Point.X + direction0.X), (float) (pointList[i].Point.Y + direction0.Y)));
                }
            }
            else
            {
                var direction1 = Vector2.Multiply(halfThickness, Vector2.Normalize(new Vector2((float) pointList[i].Point.X - (float) pointList[i - 1].Point.X, (float) pointList[i].Point.Y - (float) pointList[i - 1].Point.Y)));
                var direction2 = Vector2.Multiply(halfThickness, Vector2.Normalize(new Vector2((float) pointList[i + 1].Point.X - (float) pointList[i].Point.X, (float) pointList[i + 1].Point.Y - (float) pointList[i].Point.Y)));

                var vector11 = new Vector2(-direction1.Y, direction1.X);
                var vector12 = new Vector2(direction1.Y, -direction1.X);
                var vector21 = new Vector2(-direction2.Y, direction2.X);
                var vector22 = new Vector2(direction2.Y, -direction2.X);

                switch (-direction1.X * direction2.Y + direction1.Y * direction2.X)
                {
                    case < 0:
                        {
                            var vector1 = Vector2.Normalize(vector11 + vector21) * halfThickness;
                            var vector2 = Vector2.Normalize(vector12 + vector22) * halfThickness;

                            outlinePointList1.Add(new SKPoint((float) (pointList[i].Point.X + vector1.X), (float) (pointList[i].Point.Y + vector1.Y)));
                            outlinePointList2.Add(new SKPoint((float) (pointList[i].Point.X + vector12.X), (float) (pointList[i].Point.Y + vector12.Y)));
                            outlinePointList2.Add(new SKPoint((float) (pointList[i].Point.X + vector2.X), (float) (pointList[i].Point.Y + vector2.Y)));
                            outlinePointList2.Add(new SKPoint((float) (pointList[i].Point.X + vector22.X), (float) (pointList[i].Point.Y + vector22.Y)));
                            break;
                        }
                    case > 0:
                        {
                            var vector1 = Vector2.Normalize(vector11 + vector21) * halfThickness;
                            var vector2 = Vector2.Normalize(vector12 + vector22) * halfThickness;

                            outlinePointList1.Add(new SKPoint((float) (pointList[i].Point.X + vector11.X), (float) (pointList[i].Point.Y + vector11.Y)));
                            outlinePointList1.Add(new SKPoint((float) (pointList[i].Point.X + vector1.X), (float) (pointList[i].Point.Y + vector1.Y)));
                            outlinePointList1.Add(new SKPoint((float) (pointList[i].Point.X + vector21.X), (float) (pointList[i].Point.Y + vector21.Y)));
                            outlinePointList2.Add(new SKPoint((float) (pointList[i].Point.X + vector2.X), (float) (pointList[i].Point.Y + vector2.Y)));
                            break;
                        }
                    default:
                        outlinePointList1.Add(new SKPoint((float) (pointList[i].Point.X + vector11.X), (float) (pointList[i].Point.Y + vector11.Y)));
                        outlinePointList1.Add(new SKPoint((float) (pointList[i].Point.X + vector21.X), (float) (pointList[i].Point.Y + vector21.Y)));
                        outlinePointList2.Add(new SKPoint((float) (pointList[i].Point.X + vector12.X), (float) (pointList[i].Point.Y + vector12.Y)));
                        outlinePointList2.Add(new SKPoint((float) (pointList[i].Point.X + vector22.X), (float) (pointList[i].Point.Y + vector22.Y)));
                        break;
                }
            }
        }

        var outlinePoints = new SKPoint[outlinePointList1.Count + outlinePointList2.Count + 1];
        outlinePointList2.Reverse();
        outlinePointList1.CopyTo(outlinePoints, 0);
        outlinePointList2.CopyTo(outlinePoints, outlinePointList1.Count);
        outlinePoints[^1] = outlinePoints[0];
        return outlinePoints;
    }

    private readonly List<SKPoint> _outlinePointList1 = new List<SKPoint>();
    private readonly List<SKPoint> _outlinePointList2 = new List<SKPoint>();
}