裁剪圖像的一部分

Question

我想裁剪圖像的一部分。 我的計划是用圖像創建一個圖層，但是圖像使該圖層溢出。

它看起來像這樣的例子：

有任何想法嗎？ 謝謝。

using (CGLayer starLayer = CGLayer.Create (g, rect.Size)) {
            // set fill to blue
            starLayer.Context.SetFillColor (0f, 0f, 1f, 0.4f);
            starLayer.Context.AddLines (myStarPoints);

            starLayer.Context.AddQuadCurveToPoint(this.points [3].X, this.points [3].Y, this.points [2].X, this.points [2].Y);
            starLayer.Context.AddQuadCurveToPoint(this.points [5].X, this.points [5].Y, this.points [4].X, this.points [4].Y);
            starLayer.Context.FillPath ();



            double width =  Math.Abs((double)(this.points [1].X - this.points [0].X));
            float prop = this.tmpimage.Size.Width / (float)width;

            float height = (this.tmpimage.Size.Height / prop);

            double centerteeth = (Math.Sqrt (Math.Pow ((this.points [4].X - this.points [2].X), 2.0) + Math.Pow ((this.points [4].Y - this.points [2].Y), 2.0))) / 2 - (width/2);



            starLayer.Context.DrawImage (new RectangleF ((float)centerteeth + this.points[2].X, this.points [2].Y, (float)width, height), this.imagerotated.CGImage);


            // draw the layer onto our screen
            float starYPos = 5;
            float starXPos = 5;


            g.DrawLayer (starLayer, new PointF (starXPos, starYPos));



        }

Answer 1

如果您正在尋找一種快速的解決方案來完成它，可以使用兩個圖像來完成所需的工作嗎？ （一個黑色的圖像，然后是背景）將一個UIImageView放在另一個之上？

我通常僅出於以下兩個原因而開始使用CoreGraphics ：

• 沒有其他方法可以實現我的目標
• 使用普通的UIViews性能不夠

Answer 2

現在，我找到了一個對我有用的解決方案，無論如何，謝謝您的幫助。

imagessublayer可在主層中移動。

那就是我的解決方案：

        CALayer imageLayer = new CALayer (Layer);
        imageLayer.Frame = Layer.Bounds;
        imageLayer.BackgroundColor = UIColor.Black.CGColor;


        CAShapeLayer maskLayer = new CAShapeLayer();
        maskLayer.FillRule = CAShapeLayer.FillRuleEvenOdd;
        maskLayer.Frame = Frame;


        double width =  Math.Abs((double)(this.points [1].X - this.points [0].X));
        float prop = this.tmpimage.Size.Width / (float)width;
        float height = (this.tmpimage.Size.Height / prop);


        CALayer lay = new CALayer ();
        lay.Bounds = new RectangleF (0, 0, (float)width, height);
        lay.Position = this.points[6];

        lay.Contents = this.tmpimage.CGImage;
        layers [6] = lay;

        imageLayer.AddSublayer (lay);



        CGPath p1 = new CGPath();

        p1.MoveToPoint (this.points [2]);
        p1.AddQuadCurveToPoint(this.points [3].X, this.points [3].Y, this.points [4].X, this.points [4].Y);
        p1.AddQuadCurveToPoint(this.points [5].X, this.points [5].Y, this.points [2].X, this.points [2].Y);

        maskLayer.Path = p1;

        imageLayer.Mask = maskLayer;
        Layer.AddSublayer (imageLayer);


        CAShapeLayer pathLayer1 = new CAShapeLayer ();
        pathLayer1.Path = maskLayer.Path;
        pathLayer1.LineWidth = 0f;
        pathLayer1.StrokeColor = UIColor.Clear.CGColor;
        pathLayer1.FillColor = UIColor.Clear.CGColor;
        Layer.AddSublayer (pathLayer1);