addText 函数

-(UIImage *)addText:(UIImage *)img text:(NSString *)text1
{
    //get image width and height
    int w = img.size.width;
    int h = img.size.height;
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    //create a graphic context with CGBitmapContextCreate
    CGContextRef context = CGBitmapContextCreate(NULL, w, h, 8, 4 * w, colorSpace, kCGImageAlphaPremultipliedFirst);
    CGContextDrawImage(context, CGRectMake(0, 0, w, h), img.CGImage);
    CGContextSetRGBFillColor(context, 0.0, 1.0, 1.0, 1);
    char* text = (char *)[text1 cStringUsingEncoding:NSASCIIStringEncoding];
    CGContextSelectFont(context, "Georgia", 30, kCGEncodingMacRoman);
    CGContextSetTextDrawingMode(context, kCGTextFill);
    CGContextSetRGBFillColor(context, 255, 0, 0, 1);
    CGContextSetTextMatrix(context, CGAffineTransformMakeRotation( -M_PI/4 ));
    CGContextShowTextAtPoint(context, 60, 390, text, strlen(text));
    //Create image ref from the context
    CGImageRef imageMasked = CGBitmapContextCreateImage(context);
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    return [UIImage imageWithCGImage:imageMasked];

}