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Drawing Quick Response Code in Objective-C Graphics: Quartz, Core Animation, and OpenGL

Graphics: Quartz, Core Animation, and OpenGL
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We re not quite done with Quartz yet. Before we finish up this chapter, we re going to put together a more fully featured example combining some of the Quartz lessons from this chapter with some of the photographic work we covered in chapter 18.
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19.6 Drawing on a picture: an example
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To put together the lessons we ve covered, you re going to create a program that allows a user to load up a picture, draw on it, and then save the results. Figure 19.5 shows our intended result. As usual, you ll start in Interface Builder, but you only have two simple things to do here:
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Create a UIButtonBar with a single action-type button (which is one of the standard styles you can select for a button). Link the existing UIView to a new drawView class (which should be a UIView subclass).
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Once you get into Xcode, the programming will look a lot like the collage program in the last chapter, but with some nuances related to your greater understanding of Quartz. You ll be doing your coding in two parts. The overall structure of the program will go in photodrawViewController.m and the drawing specifics will go in drawView.m.
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Figure 19.5 Photodraw can place drawings on pictures.
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19.6.1 The photodraw view controller
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The view controller manages an image selector as well as several toolbar buttons, including the action button that you created in Interface Builder and Save and Cancel buttons that will appear later on. The code is shown in listing 19.7. We ve omitted some of the view controller s overall structure and focused on the code that s involved when the user pushes the action button and activates choosePic:.
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Listing 19.7 The important bits of a view controller for a photodraw program
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-(IBAction)choosePic:(id)sender { UIImagePickerController *myImagePicker = [[UIImagePickerController alloc] init]; myImagePicker.delegate = self; myImagePicker.allowsImageEditing = NO; } - (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)image
Starts image picker
[self presentModalViewController:myImagePicker animated:YES];
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editingInfo:(NSDictionary *)editingInfo { [self dismissModalViewControllerAnimated:YES]; [picker release];
387 Finishes image picker
[myTools setItems:[NSArray arrayWithObjects: [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemSave target:self action:@selector(savePic:)], [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemCancel target:self action:@selector(clearDrawing:)], nil] animated:YES]; [self.view drawPic:image]; } - (void)imagePickerControllerDidCancel: (UIImagePickerController *)picker {
Resolves image cancellation
[self dismissModalViewControllerAnimated:YES]; [picker release]; } - (void)savePic:(id)sender {
Saves picture
UIGraphicsBeginImageContext(self.view.bounds.size); [myTools removeFromSuperview]; [self.view.layer renderInContext:UIGraphicsGetCurrentContext()]; UIImage *finishedPic = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); UIImageWriteToSavedPhotosAlbum(finishedPic,self, @selector(exitProg:didFinishSavingWithError:contextInfo:),nil); } - (void)exitProg:(UIImage *)image didFinishSavingWithError:(NSError *)error contextInfo:(void *)contextInfo {
Ends program
exit(0); } -(void)clearDrawing:(id)sender { [self.view cancelDrawing]; }
Clears drawing
This is a pretty simple snippet of code because it shows the view controller acting as a traffic cop, accepting input from controls and sending off messages to other objects, which is pretty much the definition of what a view controller should do. For once, you don t have any setup in viewDidLoad:. Instead, the toolbar created in Interface Builder will initiate your program s actions. At startup, the user has only one choice, to click the action button and start the image picker B. When the picker returns, you modify the UIButtonBar to now give options for Save and Cancel, and then you send the picture off to drawView to be dealt with C. Alternatively, you clear the image picker away if the user canceled it D. The save picture routine works the same way as the one you wrote in the collage program E. The only difference is that this one includes a callback, which ends the
Graphics: Quartz, Core Animation, and OpenGL
program after the saving is done F. The clear drawing method G, meanwhile, makes a call to the drawView object again. To learn what s done with the initial picture, how drawing occurs, and what happens when the drawing is cleared, we need to look at this program s other major class.
19.6.2 The photodraw view
As we saw in the previous section, the view controller hands off three responsibilities to the view: displaying a picture, responding to touch events, and clearing the drawing. We re going to step through these functions one at a time. Listing 19.8 shows what s done when a user picks an image.
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