[Tutorial] Drawing to the screen.

can someone please help me make a clear button ?

Hello, i have a question.
I do everything follow the tutorial then build and run very good. But when i zoom in the "drawImage" object by multi touch on screen then i draw very slow and my app have CRASH.

anyone know that reason? Help me!
this is my TouchBegan method

Code:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {	
		touches = [event allTouches];
		switch ([touches count]) {
			case 1: { //Single touch	
			} break;
			case 2: { //Multi Touch
				//Track the initial distance between two fingers.
				UITouch *touch1 = [[touches allObjects] objectAtIndex:0];
				UITouch *touch2 = [[touches allObjects] objectAtIndex:1];
				initialDistance = [self distanceBetweenTwoPoints:[touch1 locationInView:[self drawImage]]
														 toPoint:[touch2 locationInView:[self drawImage]]];
			} break;
		}
}

and touchMoved Method

Code:

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
		touches = [event allTouches];
		switch ([touches count])
		{
		
			case 2: {
				//The image is being zoomed in or out.
				UITouch *touch1 = [[touches allObjects] objectAtIndex:0];
				UITouch *touch2 = [[touches allObjects] objectAtIndex:1];
				//Calculate the distance between the two fingers.
				finalDistance = [self distanceBetweenTwoPoints:[touch1 locationInView:[self drawImage]]
													   toPoint:[touch2 locationInView:[self drawImage]]];

				//Check if zoom in or zoom out.
				if(initialDistance > finalDistance&& drawImage.frame.size.width >160 && drawImage.frame.size.height >300) {		
					//here decreasing the rect width,height				
					drawImage.frame = CGRectMake(0,0, drawImage.frame.size.width - (initialDistance-finalDistance), drawImage.frame.size.height - (initialDistance-finalDistance)); 
					drawImage.center = CGPointMake(160,230);
					initialDistance = finalDistance;	
				}
				else if(initialDistance < finalDistance && drawImage.frame.size.width <740 && drawImage.frame.size.height < 880 ){
					//here increasing the rect width,height
					drawImage.frame = CGRectMake(0,0, drawImage.frame.size.width + (finalDistance-initialDistance), drawImage.frame.size.height + (finalDistance-initialDistance)) ; 
					drawImage.center = CGPointMake(160,230);
					initialDistance = finalDistance;

				}
			} break;
		}
}

Best Regards!

------------------double post merged------------------

may be this code can help you

Code:

CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);

If I put the following line of code in my Clear button the screen be cleared of all he stuff the draw on the screen ?

Code:

CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);

How about allowing drawing on a certain section of the screen ?

if you put this code before you are drawing line on the screen(an UIImageView), then instead you draw a line on screen, you will erase screen under the line you have just draw.

Code:

[COLOR="Red"]CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);[/COLOR]
//CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
.
.
.

This code like a trick.

seems no one wants to help me solve this problem. OK. I will ignore that. not allowed zoom in or zoom out. But how can i undo the picture after draw in it...?

this is a great post and works perfectly...i've been wrestling with it however for drawing in a rotated view. when i rotate to landscape the drawing is offset from the touch point by a significant factor, but the factor changes as i move my cursor around the screen. i suspect a scaling or content mode issue, but after countless hours and open ticket with apple developer support, i'm not getting anywhere. any one get this or a variant working in landscpape?

------------------double post merged------------------

drawImage.image = nil;

go back to older state

Hi, it's possible to go back to older state or undo? I've found CGContextSaveGState and CGContextRestoreGState but I don't know if is the way to do that and how to implement it

Thanks!

Build Errors

Hi Skylar

Thanks for the tutorial - this is exactly what I have been looking for.

When I ran it the first time in the simulator, I got 157 errors. I got hat fixed and it worked good.

I connected my iPad to it to run on the device, but I get two build errors I am not sure how to fix.

They are:

CFBundleIdentifier contains an illegal character

and

invalid bundle identifier

I am not sure if this is your code or me at my end?

Any ideas ?

Iain