使用 NSString drawInRect 绘制旋转文本

Question

我找到了关于如何使用 NSString drawInRect: 绘制旋转文本的答案，但我不确定它是如何工作的，因为它只对我有用：https://discussions.apple.com/thread/1779814?start=0&tstart=0

我的代码如下：

           CGContextSaveGState(context);
           CGContextDrawLinearGradient(context, gradient, CGPointMake(0, centY - halfWidth), CGPointMake(0, centY + halfWidth), 0);

            // Add text                
            CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor); 
            NSString *str = @"some test string";

            CGAffineTransform transform1 = CGAffineTransformMakeRotation(M_PI/4);

            CGContextConcatCTM(context, transform1);
            CGContextTranslateCTM(context, 0, 0);
            UIFont *font = [UIFont systemFontOfSize:16.0];

            [str drawInRect:CGRectMake(0, 0, 200, 100) withFont:font lineBreakMode:UILineBreakModeWordWrap alignment:UIBaselineAdjustmentNone];

所以当我使用它时，我看到文本在 x 轴下方 45 度处绘制。我想沿着我的线性渐变垂直绘制文本。所以我想我可以通过使用 M_PI/2 90 度来做到这一点。我没有看到我的文字。我尝试了不同的旋转变换，只有一些看起来像 M_PI/4 和 M_PI/8。我认为如果我使用 -M_PI/4 它将使文本在 x 轴上方 45 度，而 M_PI/2 将在 x 轴下方 90 度。但两者都一无所获。

有什么想法吗？谢谢。

Answer 1

我用下一个方法解决这个问题。

1) 在 NSString 上声明类别

@interface NSString (NMSchemeItemDraw)
-(void)  drawWithBasePoint:(CGPoint)basePoint
                    andAngle:(CGFloat)angle
                     andFont:(UIFont*)font;
@end

此类别将使用给定的中心点在一行中以给定的字体和角度绘制文本。

2) 这个类的实现如下：

@implementation NSString (NMSchemeItemDraw)

    -(void)  drawWithBasePoint:(CGPoint)basePoint
                     andAngle:(CGFloat)angle
                      andFont:(UIFont *)font{
    CGSize  textSize    =   [self   sizeWithFont:font];

    CGContextRef    context =   UIGraphicsGetCurrentContext();
    CGAffineTransform   t   =   CGAffineTransformMakeTranslation(basePoint.x, basePoint.y);
    CGAffineTransform   r   =   CGAffineTransformMakeRotation(angle);


    CGContextConcatCTM(context, t);
    CGContextConcatCTM(context, r);

    [self   drawAtPoint:CGPointMake(-1 * textSize.width / 2, -1 * textSize.height / 2)
               withFont:font];

    CGContextConcatCTM(context, CGAffineTransformInvert(r));
    CGContextConcatCTM(context, CGAffineTransformInvert(t));
    }
@end

3) 现在我可以在我的[UIView drawRect:] 方法中使用它。 例如，在下一个方式：

 -(void)drawRect:(CGRect)rect{
 NSString* example = @"Title";
 [example drawWithBasePoint:CGPointMake(0.0f, 0.0f)
                   andAngle:M_PI
                    andFont:[UIFont boldSystemFontOfSize:16.0]];
 }

Answer 2

我认为正在发生的事情是您将文本旋转到视图之外的位置，因为它通过旋转原点来旋转上下文。

旋转后，您需要进行平移以将上下文移回视图中。在下面的示例中，我将上下文逆时针旋转 90 度。然后我将上下文的 tx 转换为高度的距离。

- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext(); 

    CGContextSaveGState(context);

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    // Create the gradient 
    CGColorRef startColor = [UIColor colorWithRed:1.0 green:1.0 blue:1.0 alpha:1.0].CGColor; 
    CGColorRef endColor = [UIColor colorWithRed:200.0/255.0 green:200.0/255.0 blue:200.0/255.0 alpha:1.0].CGColor;
    NSArray *colors = [NSArray arrayWithObjects:(id)startColor, (id)endColor, nil];
    CGFloat locations[] = { 0.0, 1.0 };
    CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (CFArrayRef) colors, locations);
    CGContextDrawLinearGradient(context, gradient, CGPointMake(rect.origin.x + rect.size.width / 2, rect.origin.y), CGPointMake(rect.origin.x + rect.size.width / 2, rect.origin.y + rect.size.height), 0);

    // Create text              
    CGContextSetFillColorWithColor(context, [UIColor blackColor].CGColor); 
    NSString *string = @"some test string";
    UIFont *font = [UIFont systemFontOfSize:16.0];

    // Rotate the context 90 degrees (convert to radians)
    CGAffineTransform transform1 = CGAffineTransformMakeRotation(-M_PI_2);
    CGContextConcatCTM(context, transform1); 

    // Move the context back into the view 
    CGContextTranslateCTM(context, -rect.size.height, 0);

    // Draw the string 
    [string drawInRect:rect withFont:font lineBreakMode:UILineBreakModeWordWrap alignment:UITextAlignmentLeft];

    // Clean up 
    CGGradientRelease(gradient);
    CGColorSpaceRelease(colorSpace);

    CGContextRestoreGState(context);
}

请注意，您还可以获取如何呈现字符串的大小，这有助于计算文本的对齐方式。

    CGSize stringSize = [string sizeWithFont:font]; 

Answer 3

这是 KoNEW 答案的更新和简化版本。它保留了图形上下文的状态作为奖励。这也是一个简单的函数，而不是字符串扩展。

func drawRotatedText(_ text: String, at p: CGPoint, angle: CGFloat, font: UIFont, color: UIColor) {
  // Draw text centered on the point, rotated by an angle in degrees moving clockwise.
  let attrs = [NSFontAttributeName: font, NSForegroundColorAttributeName: color]
  let textSize = text.size(attributes: attrs)
  let c = UIGraphicsGetCurrentContext()!
  c.saveGState()
  // Translate the origin to the drawing location and rotate the coordinate system.
  c.translateBy(x: p.x, y: p.y)
  c.rotate(by: angle * .pi / 180)
  // Draw the text centered at the point.
  text.draw(at: CGPoint(x: -textSize.width / 2, y: -textSize.height / 2), withAttributes: attrs)
  // Restore the original coordinate system.
  c.restoreGState()
}

Answer 4

KoNew 在 Swift 中的解决方案：

extension NSString {

    func drawWithBasePoint(basePoint:CGPoint, angle:CGFloat, font:UIFont) {

        var attrs: NSDictionary = [
            NSFontAttributeName: font
        ]

        var textSize:CGSize = self.sizeWithAttributes(attrs as [NSObject : AnyObject])

        // sizeWithAttributes is only effective with single line NSString text 
        // use boundingRectWithSize for multi line text

        var context: CGContextRef =   UIGraphicsGetCurrentContext()

        var t:CGAffineTransform   =   CGAffineTransformMakeTranslation(basePoint.x, basePoint.y)
        var r:CGAffineTransform   =   CGAffineTransformMakeRotation(angle)


        CGContextConcatCTM(context, t)
        CGContextConcatCTM(context, r)


        self.drawAtPoint(CGPointMake(-1 * textSize.width / 2, -1 * textSize.height / 2), withAttributes: attrs as [NSObject : AnyObject])


        CGContextConcatCTM(context, CGAffineTransformInvert(r))
        CGContextConcatCTM(context, CGAffineTransformInvert(t))


    }


}

使用方法：

let fieldFont = UIFont(name: "Helvetica Neue", size: 14)

myNSString.drawWithBasePoint(CGPointMake(bounds.width/2, bounds.height/2), angle: CGFloat(-M_PI_2), font: fieldFont!)

Answer 5

感谢这篇文章，以及Chris's answer 和Arkadiusz's answer at another post。

最后，我通过一个名为MyVerticalLabel 的UILabel 子类解决了这个问题，并让它绘制垂直文本。

@implementation MyVerticalLabel

// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect {
    // Drawing code

    CGContextRef context = UIGraphicsGetCurrentContext();

    CGAffineTransform transform = CGAffineTransformMakeRotation(-M_PI_2);
    CGContextConcatCTM(context, transform);
    CGContextTranslateCTM(context, -rect.size.height, 0);

    // The drawing rect should be applied with transform to.
    CGRect newRect = CGRectApplyAffineTransform(rect, transform);
    newRect.origin = CGPointZero;

    NSMutableParagraphStyle *textStyle = [[NSMutableParagraphStyle defaultParagraphStyle] mutableCopy];
    textStyle.lineBreakMode = self.lineBreakMode;
    textStyle.alignment = self.textAlignment;

    // Apply current label attributes for drawing function.
    NSDictionary *attributeDict =
    @{
      NSFontAttributeName : self.font,
      NSForegroundColorAttributeName : self.textColor,
      NSParagraphStyleAttributeName : textStyle,
      };
    [self.text drawInRect:newRect withAttributes:attributeDict];
}

@end

Answer 6

我发现上面 Todd 的答案非常有帮助。但是，我经常想相对于文本的边缘之一（顶部、左侧等）定位和旋转文本。所以，我扩展了他的回答。另外，使用了属性文本，所以可以独立处理字体、颜色等。

enum StringOrigin: Int { case
    upperLeft, upperCenter, upperRight,
    centerLeft, centerCenter, centerRight,
    lowerLeft, lowerCenter, lowerRight }

func drawRotatedAttrString(_ s: NSAttributedString, p: CGPoint, angle: CGFloat, origin: StringOrigin) {
    let width = s.size().width
    let height = s.size().height

    let c = UIGraphicsGetCurrentContext()!
    c.saveGState()
    // Translate the origin to the drawing location and rotate the coordinate system.
    c.translateBy(x: p.x, y: p.y)
    c.rotate(by: angle * .pi / 180)
    // Draw the text offset to handle "origin" choice
    switch origin {
    case .upperLeft:
        s.draw(at: .zero)
    case .upperCenter:
        s.draw(at: CGPoint(x: -0.5 * width, y: 0))
    case .upperRight:
        s.draw(at: CGPoint(x: -width, y: 0))
    case .centerLeft:
        s.draw(at: CGPoint(x: 0, y: -0.5 * height))
    case .centerCenter:
        s.draw(at: CGPoint(x: -0.5 * width, y: -0.5 * height))
    case .centerRight:
        s.draw(at: CGPoint(x: -width, y: -0.5 * height))
    case .lowerLeft:
        s.draw(at: CGPoint(x: 0, y: -height))
    case .lowerCenter:
        s.draw(at: CGPoint(x: -0.5 * width, y: -height))
    case .lowerRight:
        s.draw(at: CGPoint(x: -width, y: -height))
    }
    // Restore the original coordinate system.
    c.restoreGState()
}