坐標(biāo)系

如果你了解過 iOS UIKit，你就知道坐標(biāo)的原點就在屏幕的左上角，但是底層Core Graphics的context使用的坐標(biāo)系的原點是在屏幕的左下角。那從底層到上層一定是做了轉(zhuǎn)變。蘋果官方例圖

圖1.png

 - (void)drawRect:(CGRect)rect{
    [super drawRect:rect];

    //獲得當(dāng)前的Graphics Context
    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextSetTextMatrix(context, CGAffineTransformIdentity);
    //向上平移一個視圖高度的距離
    CGContextTranslateCTM(context, 0, self.bounds.size.height);
    //圍繞x軸的翻轉(zhuǎn)
    CGContextScaleCTM(context, 1.0, -1.0);
   }

寫一小段文字效果：

圖2.png

- (void)drawRect:(CGRect)rect
{
[super drawRect:rect];

//獲得當(dāng)前的Graphics Context
CGContextRef context = UIGraphicsGetCurrentContext();

CGContextSetTextMatrix(context, CGAffineTransformIdentity);
//向上平移一個視圖高度的距離
CGContextTranslateCTM(context, 0, self.bounds.size.height);
//圍繞x軸的翻轉(zhuǎn)
CGContextScaleCTM(context, 1.0, -1.0);


// 創(chuàng)建繪制區(qū)域
CGMutablePathRef path = CGPathCreateMutable();
CGPathAddRect(path, NULL, self.bounds);

//文字相關(guān)的屬性都是由NSMutableAttributedString來設(shè)置的
NSMutableAttributedString *att = [[NSMutableAttributedString alloc] initWithString:@"愛笑的女孩運氣不會太差，太差你倒是也笑不出來的"];
[att addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:25] range:NSMakeRange(4, 5)];
[att addAttribute:NSFontAttributeName value:[UIFont boldSystemFontOfSize:20] range:NSMakeRange(11, 4)];
[att addAttribute:NSForegroundColorAttributeName value:[UIColor purpleColor] range:NSMakeRange(3, 4)];

//上下行的間距
CGFloat lineSpace = 30 ;

const CFIndex num = 1;
CTParagraphStyleSetting theSettings[num] = {
            {kCTParagraphStyleSpecifierLineSpacingAdjustment,sizeof(CGFloat),&lineSpace},
};
CTParagraphStyleRef theParagraphRef = CTParagraphStyleCreate(theSettings, num);

// NSMakeRange(0, att.length) 整段文字長度
[att addAttribute:NSParagraphStyleAttributeName value:(__bridge id)(theParagraphRef) range:NSMakeRange(0, att.length)];



//排版
CTFramesetterRef framesetter =
CTFramesetterCreateWithAttributedString((CFAttributedStringRef)att);
CTFrameRef frame =
CTFramesetterCreateFrame(framesetter,
                         CFRangeMake(0, [att length]), path, NULL);

//繪制
CTFrameDraw(frame, context);

//釋放
CFRelease(theParagraphRef);
CFRelease(frame);
CFRelease(path);
CFRelease(framesetter);
}