Why is my text flip over when using CGContextShowAtPoint?

I am writing a simple practice. However, my text is flip upside 开发者_StackOverflow社区down when I trying to use CGContext to put some string on the UIView, I am wondering why and how to change it into correct format.

Here is my code in the drawRect

    char *string = "TEST";
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextBeginPath(context);
CGContextSelectFont (context,"Helvetica-Bold",12, kCGEncodingMacRoman); 

CGContextShowTextAtPoint(context, 5, 5, string, strlen(string));

CGContextClosePath(context);

Thanx for your help.

CoreGraphics uses cartesian coordinates, so you need to translate your context before doing any drawing

CGContextRef context = UIGraphicsGetCurrentContext();

// transforming context
CGContextTranslateCTM(context, 0.0, rect.size.height);
CGContextScaleCTM(context, 1.0, -1.0);

// your drawing code

Quartz2D has an inverted y axis - handy eh? If you are inside a drawRect method, you can use the following to flip the text over.

CGContextTranslateCTM(context, 0.0, rect.size.height);
CGContextScaleCTM(context, 1.0, -1.0);

Another way is;

transform = CGAffineTransformMake(1.0,0.0,0.0,-1.0,0.0,0.0);
CGContextSetTextMatrix(context, transform);

Or on one line;

CGContextSetTextMatrix(context, CGAffineTransformMake(1.0,0.0, 0.0, -1.0, 0.0, 0.0));

Use the UIKit additions in NSString:

NSString *string = @"TEST";
[string drawAtPoint:CGPointMake(5, 5)
           withFont:[UIFont boldSystemFontOfSize:12]];