基于CoreText的基础排版引擎之不带图片的排版引擎

- (void)drawRect:(CGRect)rect {

[super drawRect:rect];

//步骤一:得到当前绘制画布上下文，用于后续将内容绘制在画布上

CGContextRef context = UIGraphicsGetCurrentContext();

//步骤二：将坐标系上下翻转。对于底层的绘制引擎来说，屏幕左下角是（0，0）坐标。而对于上层的UIKit来说，左上角是（0，0）坐标。所以我们为了之后的坐标系描述按UIKit来显示，这里做了一个坐标系上下翻转操作。翻转之后，底层和上层的（0，0）坐标就是重合的了。

CGContextSetTextMatrix(context, CGAffineTransformIdentity);

CGContextTranslateCTM(context, 0, self.bounds.size.height);

CGContextScaleCTM(context, 1.0, -1.0);

//步骤三：创建绘制区域

CGMutablePathRef path = CGPathCreateMutable();

CGPathAddRect(path, NULL, self.bounds);

//    CGPathAddEllipseInRect(path, NULL, self.bounds);

//步骤四

NSAttributedString *attString = [[NSAttributedString alloc] initWithString:@"ScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhang"];

CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)attString);

CTFrameRef frame = CTFramesetterCreateFrame(framesetter, CFRangeMake(0, [attString length]), path, NULL);

//步骤五

CTFrameDraw(frame, context);

//步骤六

CFRelease(frame);

CFRelease(path);

CFRelease(framesetter);

}