c# - Xamarin iOS CGPath 绘制带有弯角/圆角的多边形

Question

我正在尝试创建一个在自定义 UIView 子类中绘制多边形的类。我已经可以正常工作了，但现在我想通过将角圆化来平滑角，但我不知道该怎么做。这是我到目前为止所拥有的:

public class MyView : UIView
{
    private List<CGPoint> points;

    public MyView(CGRect frame, List<CGPoint> points) : base (frame)
    {
        this.points = points;
    }

    public override Draw (CGRect rect)
    {
        CGContext context = UIGraphics.GetCurrentContext();

        context.SetLineWidth(2);
        UIColor.Black.SetStroke();
        UIColor.Green.SetFill();

        CGPath path = new CGPath();
        path.AddLines(points.ToArray());
        path.CloseSubpath();

        context.AddPath(path);
        context.Clip();

        using (CGColorSpace rgb = CGColorSpace.CreateDeviceRGB())
        {
            CGGradient gradient = new CGGradient (rgb, new CGColor[]
            {
                new CGColor(0, 1, 0),
                new CGColor(0, 0.5f, 0),
                new CGColor(0, 1, 0),
                new CGColor(0, 0.5f, 0)
            });

            context.DrawLinearGradient(gradient,
                new CGPoint (path.BoundingBox.Left, path.BoundingBox.Top), 
                new CGPoint (path.BoundingBox.Right, path.BoundingBox.Bottom), 
                CGGradientDrawingOptions.DrawsBeforeStartLocation);
        }
    }
}

根据我提出的观点，我得到了:

我尝试过使用 path.AddCurveToPoint 和 path.AddArc 但我似乎无法让它们按照我想要的方式工作。任何帮助将不胜感激。

编辑

我尝试了 path.AddCurveToPoint，现在它看起来像这样:

一开始是正确的，但后来就完全疯了。不确定我在这里做错了什么。这是我更新的 Draw 覆盖:

public override Draw (CGRect rect)
{
    CGContext context = UIGraphics.GetCurrentContext();

    context.SetLineWidth(2);
    UIColor.Black.SetStroke();
    UIColor.Green.SetFill();

    CGPath path = new CGPath();
    path.AddLines(points.ToArray());
    path.CloseSubpath();
    // updated section
    int count = points.Count;

    for (int x = 1; x < count; x++)
    {
        var p = points[x];
        if (x != 0)
        {
            var prev = points[x - 1];
            if (prev.Y != p.Y)
            {
                if (prev.Y > p.Y)
                {
                    path.AddCurveToPoint(prev, new CGPoint(p.X - prev.X, p.Y), p);
                }
                else
                {
                    //???
                }
            }
        }
    }
    // end updated section
    context.AddPath(path);
    context.Clip();

    using (CGColorSpace rgb = CGColorSpace.CreateDeviceRGB())
    {
        CGGradient gradient = new CGGradient (rgb, new CGColor[]
        {
            new CGColor(0, 1, 0),
            new CGColor(0, 0.5f, 0),
            new CGColor(0, 1, 0),
            new CGColor(0, 0.5f, 0)
        });

        context.DrawLinearGradient(gradient,
            new CGPoint (path.BoundingBox.Left, path.BoundingBox.Top), 
            new CGPoint (path.BoundingBox.Right, path.BoundingBox.Bottom), 
            CGGradientDrawingOptions.DrawsBeforeStartLocation);
    }
}

Answer 1

更新:

根据您的更新，我现在看到了您的问题。您尝试使用点列表作为贝塞尔曲线控制点和多边形角的绘制点，但这是行不通的。

“最简单”方式是使用现有的点列表作为控制点，并在每个控制点之间创建中途结，并向每个线段添加四边形曲线。

注意:更难的方法是使用点列表作为结，并为每个贝塞尔曲线段创建控制点。我不会在这里讨论它，但许多图表系统都使用这个 article作为它们的引用，getControlPoints 的返回值将用作 AddCurveToPoint 方法的控制点。

简单的方法示例:

var color = UIColor.Red;
var color2 = UIColor.White;

var points = new List<CGPoint>() { 
    new CGPoint(136.49f, 134.6f),
    new CGPoint(197.04f, 20.0f),
    new CGPoint(257.59f, 20.0f),
    new CGPoint(303.0f, 134.6f),
    new CGPoint(303.0f, 252.0f),
    new CGPoint(28.0f, 252.0f),
    new CGPoint(28.0f, 134.6f),
    new CGPoint(136.49f, 134.6f)
};

UIBezierPath polygonPath = new UIBezierPath();
polygonPath.MoveTo(points[0]);
polygonPath.AddLineTo(points[1]);
polygonPath.AddLineTo(points[2]);
polygonPath.AddLineTo(points[3]);
polygonPath.AddLineTo(points[4]);
polygonPath.AddLineTo(points[5]);
polygonPath.AddLineTo(points[6]);
polygonPath.ClosePath();
polygonPath.Fill();
color2.SetStroke();
polygonPath.LineWidth = 10.0f;
polygonPath.Stroke();

UIBezierPath smoothedPath = new UIBezierPath();
var m0 = MidPoint(points[0], points[1]);
smoothedPath.MoveTo(m0);
smoothedPath.AddQuadCurveToPoint(m0, points[0]);
var m1 = MidPoint(points[1], points[2]);
smoothedPath.AddQuadCurveToPoint(m1, points[1]);
var m2 = MidPoint(points[2], points[3]);
smoothedPath.AddQuadCurveToPoint(m2, points[2]);
var m3 = MidPoint(points[3], points[4]);
smoothedPath.AddQuadCurveToPoint(m3, points[3]);
var m4 = MidPoint(points[4], points[5]);
smoothedPath.AddQuadCurveToPoint(m4, points[4]);
var m5 = MidPoint(points[5], points[6]);
smoothedPath.AddQuadCurveToPoint(m5, points[5]);
var m6 = MidPoint(points[6], points[0]);
smoothedPath.AddQuadCurveToPoint(m6, points[6]);

smoothedPath.AddQuadCurveToPoint(m0, points[0]); 
smoothedPath.ClosePath();

color.SetStroke();
smoothedPath.LineWidth = 5.0f;
smoothedPath.Stroke();

原文:

1) 我不确定您正在寻找多少联合平滑，但是 CGLineJoin.Round 对于 上的 LineJoinStyle UIBezierPath 将创建微妙的外观。

2) 如果需要重度拐角平滑，可以手动计算每条线的起点/终点，并添加 ArcWithCenter 来连接每条线段。

3) 或者，无需手动角弧计算，您可以在使用 CGLineJoin.Round 时设置非常粗的线宽，并将绘图尺寸稍微缩小以弥补增加的线宽。

示例:

var color = UIColor.FromRGBA(0.129f, 0.467f, 0.874f, 1.000f);

UIBezierPath polygonPath = new UIBezierPath();
polygonPath.MoveTo(new CGPoint(136.49f, 134.6f));
polygonPath.AddLineTo(new CGPoint(197.04f, 20.0f));
polygonPath.AddLineTo(new CGPoint(257.59f, 20.0f));
polygonPath.AddLineTo(new CGPoint(303.0f, 134.6f));
polygonPath.AddLineTo(new CGPoint(303.0f, 252.0f));
polygonPath.AddLineTo(new CGPoint(28.0f, 252.0f));
polygonPath.AddLineTo(new CGPoint(28.0f, 134.6f));
polygonPath.AddLineTo(new CGPoint(136.49f, 134.6f));
polygonPath.ClosePath();
polygonPath.LineJoinStyle = CGLineJoin.Round;

color.SetFill();
polygonPath.Fill();
color.SetStroke();
polygonPath.LineWidth = 30.0f;
polygonPath.Stroke();

:中点法

protected CGPoint MidPoint(CGPoint first, CGPoint second)
{
    var x = (first.X + second.X) / 2;
    var y = (first.Y + second.Y) / 2;
    return new CGPoint(x: x, y: y);
}