如何在Objective-C（iOS）中的图像上写文字？

时间：2011-08-09 07:33:04

标签： ios iphone uiimageview

我想以编程方式制作这样的图像：

example

我有上图和文字。我应该在图像上写文字吗？

我想让它成为一个完整的.png图像（图像+标签）并将其设置为按钮的背景。

15 个答案:

答案 0 :(得分：175)

在图像中绘制文本并返回结果图像：

+(UIImage*) drawText:(NSString*) text 
             inImage:(UIImage*)  image 
             atPoint:(CGPoint)   point 
{

    UIFont *font = [UIFont boldSystemFontOfSize:12];
    UIGraphicsBeginImageContext(image.size);
    [image drawInRect:CGRectMake(0,0,image.size.width,image.size.height)];
    CGRect rect = CGRectMake(point.x, point.y, image.size.width, image.size.height);
    [[UIColor whiteColor] set];
    [text drawInRect:CGRectIntegral(rect) withFont:font]; 
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return newImage;
}

用法：

// note: replace "ImageUtils" with the class where you pasted the method above
UIImage *img = [ImageUtils drawText:@"Some text"
                            inImage:img 
                            atPoint:CGPointMake(0, 0)];

将图像内部文本的原点从0,0更改为您喜欢的任何位置。

要在文本后面绘制纯色矩形，请在第[[UIColor whiteColor] set];行前添加以下内容：

[[UIColor brownColor] set];
CGContextFillRect(UIGraphicsGetCurrentContext(), 
                  CGRectMake(0, (image.size.height-[text sizeWithFont:font].height), 
                                  image.size.width, image.size.height));

我正在使用文字大小来计算纯色矩形的原点，但您可以用任意数字替换它。

答案 1 :(得分：34)

我对iOS 7支持的第一个答案的贡献：

+(UIImage*) drawText:(NSString*) text
             inImage:(UIImage*)  image
             atPoint:(CGPoint)   point
{
    UIGraphicsBeginImageContextWithOptions(image.size, YES, 0.0f);
    [image drawInRect:CGRectMake(0,0,image.size.width,image.size.height)];
    CGRect rect = CGRectMake(point.x, point.y, image.size.width, image.size.height);
    [[UIColor whiteColor] set];

    UIFont *font = [UIFont boldSystemFontOfSize:12];
    if([text respondsToSelector:@selector(drawInRect:withAttributes:)])
    {
        //iOS 7
        NSDictionary *att = @{NSFontAttributeName:font};
        [text drawInRect:rect withAttributes:att];
    }
    else
    {
        //legacy support
        [text drawInRect:CGRectIntegral(rect) withFont:font];
    }

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return newImage;
}

希望这有帮助

编辑：修改了UIGraphicsBeginImageContextWithOptions以处理屏幕比例。 @SoftDesigner

答案 2 :(得分：19)

这是Swift版本。

func textToImage(drawText: NSString, inImage: UIImage, atPoint:CGPoint)->UIImage{

    // Setup the font specific variables
    var textColor: UIColor = UIColor.whiteColor()
    var textFont: UIFont = UIFont(name: "Helvetica Bold", size: 12)!

    //Setup the image context using the passed image.
    UIGraphicsBeginImageContext(inImage.size)

    //Setups up the font attributes that will be later used to dictate how the text should be drawn
    let textFontAttributes = [
        NSFontAttributeName: textFont,
        NSForegroundColorAttributeName: textColor,
    ]

    //Put the image into a rectangle as large as the original image.
    inImage.drawInRect(CGRectMake(0, 0, inImage.size.width, inImage.size.height))

    // Creating a point within the space that is as bit as the image.
    var rect: CGRect = CGRectMake(atPoint.x, atPoint.y, inImage.size.width, inImage.size.height)

    //Now Draw the text into an image.
    drawText.drawInRect(rect, withAttributes: textFontAttributes)

    // Create a new image out of the images we have created
    var newImage: UIImage = UIGraphicsGetImageFromCurrentImageContext()

    // End the context now that we have the image we need
    UIGraphicsEndImageContext()

    //And pass it back up to the caller.
    return newImage

}

要调用它，您只需传入图像。

textToImage("000", inImage: UIImage(named:"thisImage.png")!, atPoint: CGPointMake(20, 20))

以下链接帮助我顺利完成。

Swift - Drawing text with drawInRect:withAttributes:

How to write text on image in Objective-C (iOS)?

最初的目标是创建一个动态图像，我可以在AnnotaionView中使用它，例如在地图上的给定位置加价，这对它来说非常有用。希望这有助于某些人尝试做同样的事情。

答案 3 :(得分：18)

仅限iOS7。

右下角的水印。

@interface UIImage (DrawWatermarkText)
-(UIImage*)drawWatermarkText:(NSString*)text;
@end
@implementation UIImage (DrawWatermarkText)
-(UIImage*)drawWatermarkText:(NSString*)text {
    UIColor *textColor = [UIColor colorWithWhite:0.5 alpha:1.0];
    UIFont *font = [UIFont systemFontOfSize:50];
    CGFloat paddingX = 20.f;
    CGFloat paddingY = 20.f;

    // Compute rect to draw the text inside
    CGSize imageSize = self.size;
    NSDictionary *attr = @{NSForegroundColorAttributeName: textColor, NSFontAttributeName: font};
    CGSize textSize = [text sizeWithAttributes:attr];
    CGRect textRect = CGRectMake(imageSize.width - textSize.width - paddingX, imageSize.height - textSize.height - paddingY, textSize.width, textSize.height);

    // Create the image
    UIGraphicsBeginImageContext(imageSize);
    [self drawInRect:CGRectMake(0, 0, imageSize.width, imageSize.height)];
    [text drawInRect:CGRectIntegral(textRect) withAttributes:attr];
    UIImage *resultImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return resultImage;
}
@end

用法：

UIImage *image = [UIImage imageNamed:@"mona_lisa"];
image = [image drawWatermarkText:@"Leonardo da Vinci"];

答案 4 :(得分：12)

我做了这样的事！浏览并结合一些例子后。

将文本放在图像的中间位置，根据需要调整字体大小。

UIImage *myImage = [UIImage imageNamed:@"promoicon.png"];
UIGraphicsBeginImageContext(myImage.size);
[myImage drawInRect:CGRectMake(0,0,myImage.size.width,myImage.size.height)];
UITextView *myText = [[UITextView alloc] init];
myText.font = [UIFont fontWithName:@"TrebuchetMS-Bold" size:15.0f];
myText.textColor = [UIColor whiteColor];
myText.text = NSLocalizedString(@"promotionImageText", @"");
myText.backgroundColor = [UIColor clearColor];

CGSize maximumLabelSize = CGSizeMake(myImage.size.width,myImage.size.height);
CGSize expectedLabelSize = [myText.text sizeWithFont:myText.font                     
                                          constrainedToSize:maximumLabelSize 
                                              lineBreakMode:UILineBreakModeWordWrap];

myText.frame = CGRectMake((myImage.size.width / 2) - (expectedLabelSize.width / 2),
                                  (myImage.size.height / 2) - (expectedLabelSize.height / 2),
                                  myImage.size.width,
                                  myImage.size.height);

[[UIColor whiteColor] set];
[myText.text drawInRect:myText.frame withFont:myText.font];
UIImage *myNewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

答案 5 :(得分：7)

我为UIImage创建了完全自定义的扩展，以在Swift中绘制水印：

extension UIImage{

    enum WaterMarkCorner{
        case TopLeft
        case TopRight
        case BottomLeft
        case BottomRight
    }

    func waterMarkedImage(#waterMarkText:String, corner:WaterMarkCorner = .BottomRight, margin:CGPoint = CGPoint(x: 20, y: 20), waterMarkTextColor:UIColor = UIColor.whiteColor(), waterMarkTextFont:UIFont = UIFont.systemFontOfSize(20), backgroundColor:UIColor = UIColor.clearColor()) -> UIImage{

        let textAttributes = [NSForegroundColorAttributeName:waterMarkTextColor, NSFontAttributeName:waterMarkTextFont]
        let textSize = NSString(string: waterMarkText).sizeWithAttributes(textAttributes)
        var textFrame = CGRectMake(0, 0, textSize.width, textSize.height)

        let imageSize = self.size
        switch corner{
        case .TopLeft:
            textFrame.origin = margin
        case .TopRight:
            textFrame.origin = CGPoint(x: imageSize.width - textSize.width - margin.x, y: margin.y)
        case .BottomLeft:
            textFrame.origin = CGPoint(x: margin.x, y: imageSize.height - textSize.height - margin.y)
        case .BottomRight:
            textFrame.origin = CGPoint(x: imageSize.width - textSize.width - margin.x, y: imageSize.height - textSize.height - margin.y)
        }

        /// Start creating the image with water mark
        UIGraphicsBeginImageContext(imageSize)
        self.drawInRect(CGRectMake(0, 0, imageSize.width, imageSize.height))
        NSString(string: waterMarkText).drawInRect(textFrame, withAttributes: textAttributes)

        let waterMarkedImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return waterMarkedImage
    }
}

如您所见，我为属性添加了一些默认值，因此如果您不需要更改，则可以忽略。这里有一些如何使用它的例子：

let watermark1 = image.waterMarkedImage(waterMarkText: "@yourapp")

let watermark2 = image.waterMarkedImage(waterMarkText: "your app name", corner: .TopRight, margin: CGPoint(x: 5, y: 5), waterMarkTextColor: UIColor.greenColor())

let watermark3 = image.waterMarkedImage(waterMarkText: "appName", waterMarkTextColor: UIColor.blackColor(), waterMarkTextFont: UIFont(name: "Helvatica", size: 25)!)

Swift 4.0版本：

extension UIImage
{

    enum WaterMarkCorner
    {
        case TopLeft
        case TopRight
        case BottomLeft
        case BottomRight
    }

    func waterMarkedImage(text:String, corner:WaterMarkCorner = .BottomRight, margin:CGPoint = CGPoint(x: 20, y: 20), color:UIColor = UIColor.white, font:UIFont = UIFont.systemFont(ofSize: 20), background:UIColor = UIColor.clear) -> UIImage?
    {
        let attributes = [NSAttributedStringKey.foregroundColor: color, NSAttributedStringKey.font:font]
        let textSize = NSString(string: text).size(withAttributes: attributes)
        var frame = CGRect(x: 0, y: 0, width: textSize.width, height: textSize.height)

        let imageSize = self.size
        switch corner
        {
            case .TopLeft:
                frame.origin = margin
            case .TopRight:
                frame.origin = CGPoint(x: imageSize.width - textSize.width - margin.x, y: margin.y)
            case .BottomLeft:
                frame.origin = CGPoint(x: margin.x, y: imageSize.height - textSize.height - margin.y)
            case .BottomRight:
                frame.origin = CGPoint(x: imageSize.width - textSize.width - margin.x, y: imageSize.height - textSize.height - margin.y)
        }

        // Start creating the image with water mark
        UIGraphicsBeginImageContext(imageSize)
        self.draw(in: CGRect(x: 0, y: 0, width: imageSize.width, height: imageSize.height))
        NSString(string: text).draw(in: frame, withAttributes: attributes)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image
    }

}

答案 6 :(得分：2)

这是一个Swift版本，它正确地将文本居中于图像上。这适用于各种大小的文本。

func addTextToImage(text: NSString, inImage: UIImage, atPoint:CGPoint)     -> UIImage{

    // Setup the font specific variables
    let textColor = YOURCOLOR
    let textFont = YOUR SIZE

    //Setups up the font attributes that will be later used to dictate how the text should be drawn
    let textFontAttributes = [
        NSFontAttributeName: textFont,
        NSForegroundColorAttributeName: textColor,
    ]

    // Create bitmap based graphics context
    UIGraphicsBeginImageContextWithOptions(inImage.size, false, 0.0)

    //Put the image into a rectangle as large as the original image.
    inImage.drawInRect(CGRectMake(0, 0, inImage.size.width, inImage.size.height))

    // Our drawing bounds
    let drawingBounds = CGRectMake(0.0, 0.0, inImage.size.width, inImage.size.height)

    let textSize = text.sizeWithAttributes([NSFontAttributeName:textFont])
    let textRect = CGRectMake(drawingBounds.size.width/2 - textSize.width/2, drawingBounds.size.height/2 - textSize.height/2,
        textSize.width, textSize.height)

    text.drawInRect(textRect, withAttributes: textFontAttributes)

    // Get the image from the graphics context
    let newImag = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return newImag

}

答案 7 :(得分：1)

使用此方法在图像上添加具有所选字体，颜色和大小的文本字段

//Method to add 
- (UIImage *) addText:(UIImage *)img text:(NSString *)text
{
    CGRect rect =  CGRectMake(0,0, img.size.width, img.size.height);

    // create a context according to image size
    UIGraphicsBeginImageContext(rect.size);

    // draw image
    [img drawInRect:rect];


    float fontSize = _txtvwEdit.font.pointSize*2;
    NSLog(@"Original %f new %f",_txtvwEdit.font.pointSize,fontSize);

    UIFont* font = [UIFont fontWithName:_txtvwEdit.font.fontName size:fontSize];

    CGRect textRect = CGRectMake((_txtvwEdit.frame.origin.x*2)-5,_txtvwEdit.frame.origin.y*2,_txtvwEdit.frame.size.width*2,_txtvwEdit.frame.size.height*2);

    if ([temparyGifframes count]>0)
    {
        font = [UIFont fontWithName:_txtvwEdit.font.fontName size:_txtvwEdit.font.pointSize];

        textRect =    CGRectMake(_txtvwEdit.frame.origin.x,_txtvwEdit.frame.origin.y ,_txtvwEdit.frame.size.width,_txtvwEdit.frame.size.height);

    }

    /// Make a copy of the default paragraph style
    NSMutableParagraphStyle* paragraphStyle = [[NSParagraphStyle defaultParagraphStyle] mutableCopy];
    paragraphStyle.lineBreakMode = NSLineBreakByCharWrapping;
    paragraphStyle.alignment = NSTextAlignmentLeft;

    NSDictionary *attributes = @{ NSFontAttributeName: font, NSForegroundColorAttributeName: _txtvwEdit.textColor,NSParagraphStyleAttributeName: paragraphStyle };

    // draw text
    [text drawInRect:textRect withAttributes:attributes];


    // get as image
    UIImage * image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return image; 
}

答案 8 :(得分：0)

考虑到性能，你应该避免频繁调用-drawRect：。只要CALayer保留在层次结构中，每个UIView都支持CALayer和图像作为图层内容保留在内存中。这意味着您在应用程序中看到的大多数操作，包括视图/图层的移动，旋转和缩放，不需要重绘。这意味着你可以在UIImageView上使用添加CATextLayer，如果你不需要带水印的图像。 https://developer.apple.com/library/ios/qa/qa1708/_index.html

- (void)addText:(NSString *)text inImageView:(UIImageView *)imageView { CATextLayer *textLayer = [CATextLayer layer]; UIFont *font = [UIFont systemFontOfSize:14.0f]; CGSize textSize = [text sizeWithAttributes:@{NSFontAttributeName:[UIFont systemFontOfSize:14.0f]}]; textLayer.frame = CGRectMake((imageView.size.width - textSize.width)/2, (imageView.size.height - textSize.height)/2, textSize.width, textSize.height);; textLayer.string = text; textLayer.fontSize = font.pointSize; [imageView.layer addSublayer:textLayer]; }

答案 9 :(得分：0)

在@Jano的Swift-3中答案： - 

func drawText(text:NSString ,image:UIImage ,point:CGPoint ) -> UIImage {

        let font = UIFont.boldSystemFont(ofSize: 12)
        UIGraphicsBeginImageContext(image.size)
        image.draw(in:CGRect(x: 0, y: 0, width: image.size.width, height: image.size.height) )
            let rect = CGRect(x: point.x, y: point.y, width:image.size.width, height: image.size.height )
        UIColor.white.set()
        text.draw(in: rect.integral, withAttributes: [NSFontAttributeName   : font])
        let image =  UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image!
    }

答案 10 :(得分：0)

Swift 3 

extension UIImage {

    func textToImage(drawText: NSString, atPoint:CGPoint) -> UIImage? {

        // Setup the font specific variables
        let textColor: UIColor = UIColor.white
        let textFont: UIFont = UIFont(name: "Helvetica Bold", size: 12)!

        //Setup the image context using the passed image.
        UIGraphicsBeginImageContext(self.size)

        //Setups up the font attributes that will be later used to dictate how the text should be drawn
        let textFontAttributes = [
            NSFontAttributeName: textFont,
            NSForegroundColorAttributeName: textColor,
            ] as [String : Any]

        //Put the image into a rectangle as large as the original image.
        self.draw(in: CGRect(x:0, y:0, width:self.size.width, height: self.size.height))

        // Creating a point within the space that is as bit as the image.
        let rect: CGRect = CGRect(x:atPoint.x, y:atPoint.y, width:self.size.width, height:self.size.height)

        //Now Draw the text into an image.
        drawText.draw(in: rect, withAttributes: textFontAttributes)

        // Create a new image out of the images we have created
        let newImage: UIImage? = UIGraphicsGetImageFromCurrentImageContext()

        // End the context now that we have the image we need
        UIGraphicsEndImageContext()

        //And pass it back up to the caller.
        return newImage

    }
}

答案 11 :(得分：0)

Swift 3版本的@Hossam Ghareebs回答 并添加了缺少的backgroundColor参数集成：

enum WaterMarkCorner{
    case TopLeft
    case TopRight
    case BottomLeft
    case BottomRight
}

extension UIImage{

    func waterMarkedImage(_ waterMarkText:String, corner:WaterMarkCorner = .TopRight, margin:CGPoint = CGPoint(x: 20, y: 20), waterMarkTextColor:UIColor = UIColor.black, waterMarkTextFont:UIFont = UIFont.systemFont(ofSize: 40), backgroundColor:UIColor = UIColor(white: 1.0, alpha: 0.5)) -> UIImage?{

        let textAttributes = [NSForegroundColorAttributeName:waterMarkTextColor, NSFontAttributeName:waterMarkTextFont, NSBackgroundColorAttributeName: backgroundColor]
        let textSize = NSString(string: waterMarkText).size(attributes: textAttributes)
        var textFrame = CGRect(x:0, y:0, width:textSize.width, height:textSize.height)

        let imageSize = self.size
        switch corner{
        case .TopLeft:
            textFrame.origin = margin
        case .TopRight:
            textFrame.origin = CGPoint(x: imageSize.width - textSize.width - margin.x, y: margin.y)
        case .BottomLeft:
            textFrame.origin = CGPoint(x: margin.x, y: imageSize.height - textSize.height - margin.y)
        case .BottomRight:
            textFrame.origin = CGPoint(x: imageSize.width - textSize.width - margin.x, y: imageSize.height - textSize.height - margin.y)
        }

        /// Start creating the image with water mark
        UIGraphicsBeginImageContext(imageSize)
        self.draw(in: CGRect(x:0, y:0, width:imageSize.width, height:imageSize.height))

        NSString(string: waterMarkText).draw(in: textFrame, withAttributes: textAttributes)

        let waterMarkedImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return waterMarkedImage
    }
}

答案 12 :(得分：0)

我的功能可以在45度和90度旋转的图像上添加文本水印

+(UIImage *)drawText:(NSString *)text diagonallyOnImage:(UIImage *)image rotation:(WatermarkRotation)rotation{

    UIColor *textColor = [UIColor colorWithRed:255 green:0 blue:0 alpha:0.2];//[UIColor colorWithWhite:0.5 alpha:1.0];
    UIFont *font = [UIFont systemFontOfSize:250];

    // Compute rect to draw the text inside
    NSDictionary *attr = @{NSForegroundColorAttributeName: textColor, NSFontAttributeName: font};
    CGSize textSize = [text sizeWithAttributes:attr];
    CGSize imageSize = image.size;
    // Create a bitmap context into which the text will be rendered.
    UIGraphicsBeginImageContext(textSize);
    // Render the text
    [text drawAtPoint:CGPointMake(0,0) withAttributes:attr];
    // Retrieve the image
    UIImage* img = UIGraphicsGetImageFromCurrentImageContext();

    CGImageRef imageRef = [img CGImage];
    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
    CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);


    CGContextRef bitmap = CGBitmapContextCreate(NULL, textSize.width, textSize.width, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);

    switch (rotation) {
        case WatermarkRotation90left:
            CGContextRotateCTM (bitmap, DEGREES_RADIANS(-90));
            CGContextTranslateCTM(bitmap, -textSize.width, 0);
            break;

        case WatermarkRotation90right:
            CGContextRotateCTM (bitmap, DEGREES_RADIANS(90));
            CGContextTranslateCTM(bitmap, 0, -textSize.width);
            break;

        case WatermarkRotation45ltr:
            CGContextRotateCTM (bitmap, DEGREES_RADIANS(45));
            CGContextTranslateCTM(bitmap, textSize.width/4, -textSize.width/2);
            break;

        case WatermarkRotation45rtl:
            CGContextRotateCTM (bitmap, DEGREES_RADIANS(-45));
            CGContextTranslateCTM(bitmap, -textSize.width/2, textSize.width/4);
            break;

        default:
            break;
    }

    CGContextDrawImage(bitmap, CGRectMake(0, (textSize.width/2)-(textSize.height/2), textSize.width, textSize.height), imageRef);
    CGImageRef ref = CGBitmapContextCreateImage(bitmap);
    UIImage* newImage = [UIImage imageWithCGImage:ref];

    UIGraphicsBeginImageContext( imageSize );

    // Use existing opacity as is
    [image drawInRect:CGRectMake(0,0,imageSize.width,imageSize.height)];


    if (rotation == WatermarkRotation90left) {
        [newImage drawInRect:CGRectMake(-((textSize.width/2)-(textSize.height/2)),(imageSize.height/2)-(textSize.width/2),textSize.width,textSize.width) blendMode:kCGBlendModeNormal alpha:1.0];
    }else if(rotation == WatermarkRotation90right){
        [newImage drawInRect:CGRectMake((imageSize.width-textSize.width/2)-(textSize.height/2),(imageSize.height/2)-(textSize.width/2),textSize.width,textSize.width) blendMode:kCGBlendModeNormal alpha:1.0];
    }else{
        [newImage drawInRect:CGRectMake((imageSize.width/2)-(textSize.width/2),(imageSize.height/2)-(textSize.width/2),textSize.width,textSize.width) blendMode:kCGBlendModeNormal alpha:1.0];
    }


    UIImage *mergedImage = UIGraphicsGetImageFromCurrentImageContext();


    UIGraphicsEndImageContext();
    return mergedImage;
}

轮换枚举：

typedef enum:NSUInteger{
    WatermarkRotation90left=1,
    WatermarkRotation90right,
    WatermarkRotation45ltr,
    WatermarkRotation45rtl
}WatermarkRotation;

注意：使用0在图像中心绘制水印。（switch语句的默认情况）

将此学位度宏添加到弧度：

#define DEGREES_RADIANS(angle) ((angle) / 180.0 * M_PI)

希望这会有所帮助！！！

答案 13 :(得分：0)

我根据@harish-pathak 提供的示例构建了一个解决方案。它考虑了配备 HiDPI 显示器的设备（size 是 int，而 left 和 top 是双倍的百分比）。

-(UIImage *)drawText:(NSString *)text onImage:(UIImage *)image withSize:(NSInteger)size posLeft:(double)left posTop:(double)top {
    
    // Get UI scale for HiDPI
    CGFloat scale = [[UIScreen mainScreen] scale];
    
    UIColor *textColor = [UIColor whiteColor];
    UIFont *font = [UIFont fontWithName:@"Font-Name" size:size];
    
    // Compute rect to draw the text inside
    NSDictionary *attr = @{NSForegroundColorAttributeName: textColor, NSFontAttributeName: font};
    CGSize textSize = [text sizeWithAttributes:attr];
    CGSize imageSize = image.size;
    
    // Create a bitmap context into which the text will be rendered
    UIGraphicsBeginImageContextWithOptions(textSize, NO, scale);
    
    // Render the text
    [text drawAtPoint:CGPointMake(0,0) withAttributes:attr];
    // Retrieve the image
    UIImage* img = UIGraphicsGetImageFromCurrentImageContext();

    CGImageRef imageRef = [img CGImage];
    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
    CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);
    
    // Create bitmap context for text
    CGFloat scaledTextWidth = textSize.width * scale;
    CGFloat scaledTextHeight = textSize.height * scale;
    CGContextRef textBitmap = CGBitmapContextCreate(NULL, scaledTextWidth, scaledTextHeight, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);
    
    // Scale text for HiDPI devices
    CGContextScaleCTM(textBitmap, scale, scale);
    
    // Draw image for text
    CGRect textPosition = CGRectMake(0, 0, textSize.width, textSize.height);
    CGRect textPixelAligned = CGRectIntegral(textPosition);
    CGContextDrawImage(textBitmap, textPixelAligned, imageRef);
    CGImageRef ref = CGBitmapContextCreateImage(textBitmap);
    UIImage* newImage = [UIImage imageWithCGImage:ref];
    
    // Create bitmap context into which the image will be rendered
    UIGraphicsBeginImageContextWithOptions(imageSize, NO, scale);

    // Use existing opacity as is
    [image drawInRect:CGRectMake(0,0,imageSize.width,imageSize.height)];
    
    // Create new image with blendmode "normal"
    CGFloat textLeft = (imageSize.width*left)-(textSize.width*0.5);
    CGFloat textTop = (imageSize.height*top)-(textSize.height*0.5);
    CGRect imagePosition = CGRectMake(textLeft,textTop,textSize.width,textSize.height);
    CGRect imagePixelAligned = CGRectIntegral(imagePosition);
    [newImage drawInRect:imagePixelAligned blendMode:kCGBlendModeNormal alpha:1.0];
    
    // Get merged image from context
    UIImage *mergedImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();
    return mergedImage;
}

要在图像上居中，调用函数如下：

[self drawText:@"Text" onImage:img withSize:120 posLeft:0.5 posTop:0.5];

归功于：

答案 14 :(得分：-2)

UIImageView *imageView = [UIImageView alloc];
imageView.image = [UIImage imageNamed:@"img.png"];
UILabel *label = [UILabel alloc];
label.text = @"Your text";
[imageView addsubview:label];

设置标签的框架，以便显示标签。

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