ios - MonoTouch，在 UIImageView 上绘制裁剪区域层

Question

在我们的应用程序中，我们希望能够裁剪、缩放和平移图像，但我似乎无法弄清楚应该如何在 UIImageView 上绘制裁剪区域。

我试着弄乱 coregraphics，我可以在我的图像上渲染一个带有黑色笔划的区域，但图像会翻转。不仅如此，因为我已经在图像上绘制了，我担心如果我用手势移动和缩放它，该区域也会受到影响!

朝着正确的方向插入将不胜感激!

这是我的代码并没有真正做我想要的，以展示一些研究工作。

        // Aspect ration - Currently 1:1
        const int arWidth = 1;
        const int arHeight = 1;

        UIGraphics.BeginImageContext(ImgToCrop.Frame.Size);

        var context = UIGraphics.GetCurrentContext();

        // Set the line width
        context.SetLineWidth(4);
        UIColor.Black.SetStroke();

        // Our starting points.
        float x = 0, y = 0;

        // The sizes
        float width = ImgToCrop.Frame.Width, height = ImgToCrop.Frame.Height;

        // Calculate the geometry
        if(arWidth == arHeight){
            // The aspect ration is 1:1
            width = ImgToCrop.Frame.Width;
            height = width;

            x = 0;
            y = ImgToCrop.Frame.GetMidY()-height/2;

        }

        // The rect
        var drawRect = new RectangleF(x,y,width,height);

        context.DrawImage(new RectangleF(
            ImgToCrop.Frame.X,
            ImgToCrop.Frame.Y,
            ImgToCrop.Frame.Width,
            ImgToCrop.Frame.Height),ImgToCrop.Image.CGImage);

        // Draw it
        context.StrokeRect(drawRect);
        ImgToCrop.Image = UIGraphics.GetImageFromCurrentImageContext();

Answer 1

也许这会帮助你:

    public static UIImage ScaleToSize (UIImage image, int width, int height)
    {
        UIGraphics.BeginImageContext (new SizeF (width, height));
        CGContext ctx = UIGraphics.GetCurrentContext ();
        float ratio = (float) width / (float) height;

        ctx.AddRect (new RectangleF (0.0f, 0.0f, width, height));
        ctx.Clip ();

        var cg = image.CGImage;
        float h = cg.Height;
        float w = cg.Width;
        float ar = w / h;

        if (ar != ratio) {
            // Image's aspect ratio is wrong so we'll need to crop
            float scaleY = height / h;
            float scaleX = width / w;
            PointF offset;
            SizeF crop;
            float size;

            if (scaleX >= scaleY) {
                size = h * (w / width);
                offset = new PointF (0.0f, h / 2.0f - size / 2.0f);
                crop = new SizeF (w, size);
            } else {
                size = w * (h / height);
                offset = new PointF (w / 2.0f - size / 2.0f, 0.0f);
                crop = new SizeF (size, h);
            }

            // Crop the image and flip it to the correct orientation (otherwise it will be upside down)
            ctx.ScaleCTM (1.0f, -1.0f);
            using (var copy = cg.WithImageInRect (new RectangleF (offset, crop))) {
                ctx.DrawImage (new RectangleF (0.0f, 0.0f, width, -height), copy);
            }
        } else {
            image.Draw (new RectangleF (0.0f, 0.0f, width, height));
        }

        UIImage scaled = UIGraphics.GetImageFromCurrentImageContext ();
        UIGraphics.EndImageContext ();

        return scaled;
    }