使用NSString drawInRect绘制旋转的文本

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

我的代码看起来像:

           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];

因此,当我使用它时,我看到文本被绘制在x轴下方45度.我想沿着lineargradient垂直绘制文本.所以我认为我可以通过使用M_PI/2 90度来做到这一点.我没看到我的文字.我已经为旋转尝试了不同的变换,只有一些似乎像M_PI/4和M_PI/8一样工作.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.但两者都没有出现.

有什么想法吗？谢谢.

Answer 1

我以下一个方式解决了这个问题.

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绘制文本,在一行中并使用给定的字体和角度.

2)此类别的实施如下:

@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,在下一个方面:

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

Answer 2

我认为发生的事情是你将文本旋转到视图之外的位置,因为它通过在原点上旋转来旋转上下文.

旋转后,您需要进行翻译以将上下文移回视图.在下面的示例中,我将上下文逆时针旋转90度.然后我翻译上下文的tx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,您还可以获取字符串的呈现大小,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String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:

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

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