向图像添加多行文本区域

Question

基本上，我想在图像中添加一个带有任意文本的区域。所以图像尺寸之后会变大。这就是我想出的：

public partial class ViewController : UIViewController
{
    public override void ViewDidLoad()
    {
        base.ViewDidLoad();

        string filename = "TestImage.jpg";
        string bundlePath = NSBundle.MainBundle.BundlePath;
        string sourcePath = Path.Combine(bundlePath, filename);
        string docPath = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
        string destinationPath = Path.Combine(docPath, filename);
        File.Copy(sourcePath, destinationPath, true);

        string testString = "Lorem ipsum dolor sit amet";
        this.AddTextToImage(testString, destinationPath);

        var imageView = new UIImageView(new CGRect(0, 0, 500, 500));
        imageView.ContentMode = UIViewContentMode.ScaleAspectFit;
        imageView.Image = UIImage.FromFile(destinationPath);
        this.View.AddSubview(imageView);
        this.View.BackgroundColor = UIColor.Red;
    }


    public void AddTextToImage(string texttoadd, string filepath)
    {
        UIImage image = UIImage.FromFile(filepath);
        nfloat fontSize = 16;

        nfloat fWidth = image.Size.Width;
        nfloat fHeight = image.Size.Height;
        nfloat textWidth;
        nfloat textHeight;

        CGColorSpace colorSpace = CGColorSpace.CreateDeviceRGB();

        UIFont font = UIFont.FromName("Helvetica", fontSize);
        NSParagraphStyle style = new NSMutableParagraphStyle();
        style.LineBreakMode = UILineBreakMode.WordWrap;
        NSAttributedString attributedString = new NSAttributedString(texttoadd, font: font, foregroundColor: UIColor.Blue, paragraphStyle: style);
        CGRect stringSize = attributedString.GetBoundingRect(new CGSize(fWidth, double.MaxValue), NSStringDrawingOptions.UsesLineFragmentOrigin | NSStringDrawingOptions.UsesFontLeading, null);
        textWidth = (nfloat)Math.Ceiling(stringSize.Width);
        textHeight = (nfloat)Math.Ceiling(stringSize.Height);

        nfloat fullWidth = fWidth;
        nfloat fullHeight = fHeight + textHeight;
        UIImage composition;

        using (CGBitmapContext ctx = new CGBitmapContext(IntPtr.Zero, (nint)fullWidth, (nint)fullHeight, 8, 4 * (nint)fullWidth, CGColorSpace.CreateDeviceRGB(), CGImageAlphaInfo.PremultipliedFirst))
        {
            CGRect frameRect = new CGRect(0, 0, fullWidth, fullHeight);

            ctx.SetFillColor(UIColor.Yellow.CGColor);
            ctx.FillRect(frameRect);

            CGRect imageRect = new CGRect(0, textHeight, (double)fWidth, (double)fHeight);
            ctx.DrawImage(imageRect, image.CGImage);

            CGPath stringPath = new CGPath();
            stringPath.AddRect(new CGRect(0, 0, textWidth, textHeight));
            CTFramesetter framesetter = new CTFramesetter(attributedString);
            CTFrame frame = framesetter.GetFrame(new NSRange(0, attributedString.Length), stringPath, null);
            frame.Draw(ctx);

            using (var imageRef = ctx.ToImage())
                composition = new UIImage(imageRef);
        }

        NSData data = composition.AsJPEG();
        NSError error;
        data.Save(filepath, NSDataWritingOptions.FileProtectionNone, out error);
    }
}

目前，我有以下问题：

文本被裁剪（例如 fontSize = 160;）。多行文本似乎不起作用。
文本根本不显示（例如 fontSize = 16;）。

您可以用 Objective-C、Swift 或 C# 提供答案 - 我会尝试翻译它。

Answer 1

看来是字体的问题。使用

UIFont font = UIFont.SystemFontOfSize(fontSize);

现在可以在不切断文本的情况下完成这项工作。剩下的唯一问题是，为什么？

向图像添加多行文本区域

Add multi line text area to image

image-processing

xamarin.ios

core-text

ios

xamarin