INFO-TECH

Author: Ghanshyam Maliwal

One of the basic requirement for filling any Technical forms needs attached signature. Following code describes how to add Signature functionality in your project.

SignatureViewController:

This  ViewController opens in UIPopOverViewController and holds user Signature. User sketches here on UIView using CALayer , 
CGContext classes ( Core-Data framework API) . While making Signature, if any Correction is required, than tap three times 
continuously enables incorrect signature disappear and can make new one signature . After so, tap outside UIPopOverViewController 
that displays Signature in UIImageView that appears on MainViewController.
        

SignatureViewController.h file includes : 

@interface SignatureViewController : UIViewController{
    CALayer *canvasLayer;
    CALayer *backgroundLayer;
    UIImage *cacheImage;
    CGMutablePathRef path;
    CGPoint pathPoint;
    BOOL touching;
}

SignatureViewController.m file includes  :


1) put this below code in viewDidLoad

//Set Up drawing Layer
    canvasLayer = [[CALayer layer] retain];
    canvasLayer.bounds = CGRectMake(0,0,768, 600);
    canvasLayer.position = CGPointMake(canvasLayer.bounds.size.width/2,     canvasLayer.bounds.size.height/2);
    [canvasLayer setDelegate:self];
    [self.view.layer addSublayer:canvasLayer];
    //Set up storage Layer
    backgroundLayer = [[CALayer layer] retain];
    backgroundLayer.bounds = CGRectMake(0,0,768, 600);
    backgroundLayer.position = CGPointMake(backgroundLayer.bounds.size.width/2, backgroundLayer.bounds.size.height/2);
    [backgroundLayer setDelegate:self];
    [self.view.layer addSublayer:backgroundLayer];
    //Initialize some other Variable
    cacheImage = nil;
    touching = NO;
NOTE: we are taking two Layer 
     a) Canvaslayer is used to hold signature temporarily
     b) background layer is used to hold signature permanently.
     
     
2) Implement Touches Delegate in your ViewController

  -(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
    NSLog(@"touch moving is calling");
    if(touching){
        //get the Current location of touch event
        UITouch *touch = [touches anyObject];
        pathPoint = [touch locationInView:self.view];
        CGPathAddLineToPoint(path, NULL, pathPoint.x, pathPoint.y);
        [canvasLayer setNeedsDisplay];
}
}
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *touch = [touches anyObject];
    if ([touch tapCount]==3) {
        NSLog(@"calling to hide ");
        [self resetSignature];
    }else{
        NSLog(@"touch begin is calling");
        if (touching) return;
        //Start a new Path
        path = CGPathCreateMutable();
        //set the path's starting point
        UITouch *touch = [touches anyObject];
        CGPathMoveToPoint(path, NULL, [touch locationInView:self.view].x, [touch locationInView:self.view].y); 
        touching = YES;
    }                  
}
-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{
    NSLog(@"touch end is calling");
    UITouch *touch = [touches anyObject];
    if ([touch tapCount]==3) {
        NSLog(@"calling to hide in end ");
        [self resetSignature];
    }else{
        if (!touching) return;
        //create a new image context (Bitmap based graphic context and make it current context)
        UIGraphicsBeginImageContext(CGSizeMake(backgroundLayer.bounds.size.width, backgroundLayer.bounds.size.height));
        //grab a reference to the new image context
        CGContextRef ctx = UIGraphicsGetCurrentContext();
        //push the image context to the top of the drawing stack
        UIGraphicsPushContext(ctx);
        //set the blend mode to prevent white pixels from
        //covering up the lines that have already been drawn
        CGContextSetBlendMode(ctx, kCGBlendModeDarken);
        if (cacheImage != nil) {
            //draw the cached state of the image to the image context and release it
            [cacheImage drawInRect:CGRectMake(0,0,backgroundLayer.bounds.size.width,backgroundLayer.bounds.size.height)];
            [cacheImage release];
        }
        //blend the drawing layer into the image context
        [canvasLayer drawInContext:ctx];
        
        //we're done drawing to the image context
        UIGraphicsPopContext();
        //store the image context so we can add to it again later (this is refresh Image)
        cacheImage = UIGraphicsGetImageFromCurrentImageContext();
        [cacheImage retain];
        //we're finished with the image context altogether
        UIGraphicsEndImageContext();
        touching = NO;
        //release the path
        CGPathRelease(path);
        //update the background layer (we'll need to draw the cached image to the background)
        [backgroundLayer setNeedsDisplay];
    }
}


3) This drawLayer is called when either canvas layer or background layer is going to send setNeedsDisplay message

- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx {
    
    NSLog(@"calling drawing line ");
    //this method is handling multiple layers, so first
    //determine which layer we're drawing to
    if (layer == canvasLayer) {
        //we don't want this to fire after the background layer update
        //and after the path has been released
        if (!touching) return;
        //add the path to the context
        CGContextAddPath(ctx, path);
        //set a line width and draw the path
        CGContextSetLineWidth(ctx, 2.0f);
        //CGContextSetStrokeColorWithColor(ctx, [[UIColor greenColor] CGColor]);
        CGContextStrokePath(ctx);
        //CGContextRelease(ctx);
    }
    else if (layer == backgroundLayer) {
        //remember the current state of the context
        CGContextSaveGState(ctx);
        //the cached image coordinate system is upside down, so do a backflip
        CGContextTranslateCTM(ctx, 0, backgroundLayer.bounds.size.height);
        CGContextScaleCTM(ctx, 1.0, -1.0);
        //draw the image
        CGImageRef ref = cacheImage.CGImage;
        CGContextDrawImage(ctx, backgroundLayer.bounds, ref);
        //restore the context to its pre-flipped state
        CGContextRestoreGState(ctx);
    }
}


4) We use below resetSingnature function to remover signature and create platform to get new Signature

-(void)resetSignature{
    path =nil;
    cacheImage = nil;
    canvasLayer.contents = nil;
    backgroundLayer.contents = nil;
}