2d barcode generator c# free Preparing a picture for drawing in Objective-C

Encoding Quick Response Code in Objective-C Preparing a picture for drawing

Listing 19.8 Preparing a picture for drawing
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-(void)drawPic:(UIImage *)thisPic { myPic = thisPic; [myPic retain]; [self setNeedsDisplay]; }
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This routine is simple: it saves the picture to an instance variable and then alerts the UIView that its CALayer must be drawn. We are going to save the CALayer s drawRect: method for last, so we ll look now at how the drawView class interprets touch events. This is shown in listing 19.9.
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Listing 19.9 Recording touch events
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- (void) touchesBegan:(NSSet *) touches withEvent:(UIEvent *)event {
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Sets up touches
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[myDrawing addObject:[[NSMutableArray alloc] initWithCapacity:4]]; CGPoint curPoint = [[touches anyObject] locationInView:self]; [[myDrawing lastObject] addObject:[NSNumber numberWithFloat:curPoint.x]]; [[myDrawing lastObject] addObject:[NSNumber numberWithFloat:curPoint.y]]; } - (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
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Displays touches temporarily
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CGPoint curPoint = [[touches anyObject] locationInView:self]; [[myDrawing lastObject] addObject:[NSNumber numberWithFloat:curPoint.x]]; [[myDrawing lastObject] addObject:[NSNumber numberWithFloat:curPoint.y]]; [self setNeedsDisplay]; } - (void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
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Resolves touches
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CGPoint curPoint = [[touches anyObject] locationInView:self];
Drawing on a picture: an example
[[myDrawing lastObject] addObject:[NSNumber numberWithFloat:curPoint.x]]; [[myDrawing lastObject] addObject:[NSNumber numberWithFloat:curPoint.y]]; [self setNeedsDisplay]; }
The overall concept here is pretty simple. You maintain an NSMutableArray called myDrawing as an instance variable. Within that, you create a number of NSMutableArray subarrays, each of which contains an individual path. You set up a new subarray when a touch starts B and then add the current point when the touch moves C or ends D. The result is an array that contains a complete listing of all touches. But once again, we re going to have to wait a bit to see how that s drawn. It s notable that we tell drawView to draw (via the setNeedsDisplay method) both when a touch moves and when it ends. That s because whenever the touch moves, you want to provide instant gratification by drawing what the user has sketched out so far. When the touch ends, you do the same thing. Listing 19.10 shows the method that clears all current drawings. Its functionality is pretty obvious now that we know that the list of drawings is held as an array.
Listing 19.10 Clearing drawings
-(void)cancelDrawing { [myDrawing removeAllObjects]; [self setNeedsDisplay]; }
At this point, your drawView object is maintaining two different instance variables: myPic contains the current picture and myDrawing contains an array of paths. Putting them together into a coherent whole just requires using some of the Quartz functions that we ve discussed in the last two chapters. The results are shown in listing 19.11.
Listing 19.11 Drawing from user-created variables
- (void)drawRect:(CGRect)rect { float newHeight; float newWidth; if (!myDrawing) { myDrawing = [[NSMutableArray alloc] initWithCapacity:0]; } CGContextRef ctx = UIGraphicsGetCurrentContext(); if (myPic != NULL) { float ratio = myPic.size.height/460; if (myPic.size.width/320 > ratio) { ratio = myPic.size.width/320; } newHeight = myPic.size.height/ratio; newWidth = myPic.size.width/ratio; [myPic drawInRect:CGRectMake(0,0,newWidth,newHeight)];
Graphics: Quartz, Core Animation, and OpenGL
} if ([myDrawing count] > 0) { CGContextSetLineWidth(ctx, 5); for (int i = 0 ; i < [myDrawing count] ; i++) { NSArray *thisArray = [myDrawing objectAtIndex:i]; if ([thisArray count] > 2) { float thisX = [[thisArray objectAtIndex:0] floatValue]; float thisY = [[thisArray objectAtIndex:1] floatValue]; CGContextBeginPath(ctx); CGContextMoveToPoint(ctx, thisX, thisY);
for (int j = 2; j < [thisArray count] ; j+=2) { thisX = [[thisArray objectAtIndex:j] floatValue]; thisY = [[thisArray objectAtIndex:j+1] floatValue]; CGContextAddLineToPoint(ctx, thisX,thisY); } CGContextStrokePath(ctx);
} } } }
The main bulk of this method is spent iterating through the information that you saved in other methods. There are five Quartz functions that do the drawing work. First, you draw the selected image. We ve gone back to using the UIKit methods from the last chapter B, so that your image doesn t end up upside-down. Then, you start working through the myDrawing array. Each subarray results in your program beginning a new path C and moving to the start D. As you move through the array, you add lines E. Finally, when a subarray is complete, you stroke the path F. The result allows for drawing simple lines on a picture, which can then be saved, as we saw back in the view controller. But is it possible to do more with this example As usual, the answer is Yes.
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