how to print barcode in vb.net 2008 Graphics: Quartz, Core Animation, and OpenGL in Objective-C

Draw QR-Code in Objective-C Graphics: Quartz, Core Animation, and OpenGL

image-editing functions. When you do decide to display your newly saved image, you ll see results like the image in figure 13.4. The code needed to accomplish this simple crossing out is shown in listing 13.1.

UIImage *origPic = [UIImage imageNamed:@"pier.jpg"]; UIGraphicsBeginImageContext(origPic.size); CGContextRef thisctx = UIGraphicsGetCurrentContext();

image CGContextRotateCTM(ctx, M_PI); CGContextTranslateCTM(ctx, -origPic.size.width, -origPic.size.height); CGContextDrawImage(ctx,CGRectMake(0,0,origPic.size.width, origPic.size.height),[origPic CGImage]);

image CGContextSetLineWidth(ctx, 20); CGContextBeginPath(ctx); CGContextMoveToPoint(ctx, 0, 0); CGContextAddLineToPoint(ctx, origPic.size.width,origPic.size.height); CGContextMoveToPoint(ctx, 0, origPic.size.height); CGContextAddLineToPoint(ctx, origPic.size.width, 0); CGContextSetStrokeColorWithColor(ctx, [[UIColor redColor] CGColor]); CGContextStrokePath(ctx); UIImage *newPic = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext();

The process of modifying an image involves relatively few steps. You start by creating your bitmap context. Next, you apply any transformations that you want to use for the picture B. If you want to rotate or scale the original picture, here s where you do it. Likewise, you can use a combination of translations and the context size to easily crop an image. In this example, you flip the picture over by applying a rotation and a translation, to account for the fact that CGContextDrawImage produces an inverted picture. (You ll see an alternative way to do this in the next example.) When your transformations are finished, you can draw your image and then draw whatever you want on top of it C (or modify it in some other way). Finally, you save the new picture. We ll return to the idea of drawing on pictures in section 13.6 (though we ll do it in a much more interactive way), but in the meantime we re ready to draw words.

Unlike Canvas, Quartz supports drawing words on top of your pictures. The functions required are intricate, though, and we generally suggest using UILabel or other UIKit objects and placing them on top of your Quartz objects. But if you need words in Quartz (either because you re interweaving the words with other Quartz content or because you re adding words to a picture), you ll need to use the CGContext text options. The majority of the text-related functions modify the graphical state, as described in table 13.13. The last two functions in the table draw your text.

Table 13.13 A variety of functions for drawing text in Quartz Function CGContextSelectFont Arguments context, font name, size, text encoding context, CGTextDrawingMode context, affine transform Summary Sets a font for the graphical state

Defines how to draw text in the graphical state Places a transformation matrix in the graphical state for drawing only text Sets where to draw in the graphical state Draws the text at the current position Draws the text at the specified position

You can find several other text-related functions in the CGContext reference. Most notably, if you need more control over your fonts (and particularly if you want to link up to UIFonts), you should use CGContextSetFont and CGContextSetFontSize instead of the CGContextSelectFont function that s noted here but keep in mind that you can t use CGContextShowTextAtPoint when you set your font in this alternative way. Here s a simple example of printing text in Quartz:

CGContextSelectFont (ctx, "Helvetica",20,kCGEncodingMacRoman); CGContextSetTextDrawingMode(ctx, kCGTextFill); CGAffineTransform flip = CGAffineTransformMake(1,0,0,-1,0,0); CGContextSetTextMatrix(ctx, flip); CGContextShowTextAtPoint(ctx, 20, 85, "A Quartz Example", 16);

The only thing of note is the creation of the affine transformation matrix, flip. We ve already pointed out that the text-drawing functions don t use the iPhone OS coordinate system at present. Instead, they re stored in an inverted manner, so you need to flip them over to use them correctly. (We hope that this changes in some future release of the iPhone OS.) The affine transformation shown here describes the matrix using the CGAffineTransformMake function. It effectively does the same thing as the two-part transformation in listing 13.1. In our view, it s a bit simpler but less clear. That s only the basics of using text, but it should be enough to get you started when you need to draw in Quartz.