Question

I am working on a drawing project, where I have an eraser option. The code given below is for when I start my app and draw some lines and the proceed to use the eraser. It works fine and I get the eraser effect. Now the second scenario is where I draw some 10 lines and then click on the “undo button” and undo the whole thing, then I redo the whole thing, and now when I click on the “eraser button” and try to erase some part, but instead, it will clear the whole drawing. This is what I am trying to figure out, but i’m not understanding where I am going wrong so friends, please help me out.

Below is my code.

- (void)drawRect:(CGRect)rect
{


      case DRAW:
    {
        [m_curImage drawAtPoint:CGPointMake(0, 0)];

        CGPoint mid1 = midPoint(m_previousPoint1, m_previousPoint2); 
        CGPoint mid2 = midPoint(m_currentPoint, m_previousPoint1);
        CGContextRef context = UIGraphicsGetCurrentContext(); 



        [self.layer renderInContext:context];
        CGContextMoveToPoint(context, mid1.x, mid1.y);
        CGContextAddQuadCurveToPoint(context, m_previousPoint1.x, m_previousPoint1.y, mid2.x, mid2.y); 
        CGContextSetLineCap(context, kCGLineCapRound);
        CGContextSetLineWidth(context, self.lineWidth);
        CGContextSetStrokeColorWithColor(context, self.lineColor.CGColor);
        CGContextSetAlpha(context, self.lineAlpha);
        CGContextSetAllowsAntialiasing(context, YES);
        CGContextStrokePath(context); 
       //            [super drawRect:rect];           
    }
         break;



        case ERASE:
        {
            [m_curImage drawAtPoint:CGPointMake(0, 0)];
            CGContextRef context = UIGraphicsGetCurrentContext();     
            CGContextClearRect(context, rect);                
            CGContextSetBlendMode(context, kCGBlendModeClear);
            [super drawRect:rect];
            break;                

  }      


        case UNDO:
        {
            [m_curImage drawInRect:self.bounds];
             break;

        }

        case REDO:
        {
            [m_curImage drawInRect:self.bounds];  
             break;           
        }


        default:
            break;
    }    
}

These are functions that run when I click on undo/redo.

-(void)redrawLine
{
    UIGraphicsBeginImageContextWithOptions(self.bounds.size, NO, 0.0f);
    [self.layer renderInContext:UIGraphicsGetCurrentContext()];
    NSDictionary *lineInfo = [m_lineArray lastObject];
    m_curImage = (UIImage*)[lineInfo valueForKey:@"IMAGE"];
    UIGraphicsEndImageContext();
    [self setNeedsDisplayInRect:self.bounds];   
}


-(void)undoButtonClicked
{
    if([m_lineArray count] > 0)
    {
        NSMutableArray *line = [m_lineArray lastObject];
        [m_bufferArray addObject:line];
        [m_lineArray removeLastObject];
        [self redrawLine];
    }
    m_drawStep = UNDO;

}

-(void)redoButtonClicked
{
    if([m_bufferArray count] > 0)
    {
        NSMutableArray *line = [m_bufferArray lastObject];
        [m_lineArray addObject:line];
        [m_bufferArray removeLastObject];        
        [self redrawLine];
    }
     m_drawStep = REDO;

}

Please tell me whether I am doing it right.

Regards,

Ranjit

Answer 1

I have solved this issue, the problem and below is the code which works perfectly

case :ERASE
{
 CGPoint mid1 = midPoint(m_previousPoint1, m_previousPoint2); 
            CGPoint mid2 = midPoint(m_currentPoint, m_previousPoint1);

            [m_curImage drawAtPoint:CGPointMake(0, 0)];
            CGContextRef context = UIGraphicsGetCurrentContext(); 

            [self.layer renderInContext:context];
            CGContextMoveToPoint(context, mid1.x, mid1.y);
            CGContextAddQuadCurveToPoint(context, m_previousPoint1.x, m_previousPoint1.y, mid2.x, mid2.y); 
            CGContextSetLineCap(context, kCGLineCapRound);


            CGContextSetBlendMode(context, kCGBlendModeClear);
            CGContextSetLineJoin(context, kCGLineJoinRound);
            CGContextSetLineWidth(context, self.lineWidth);
            CGContextSetStrokeColorWithColor(context, self.lineColor.CGColor);
            CGContextSetShouldAntialias(context, YES);  
            CGContextSetAllowsAntialiasing(context, YES); 
            CGContextSetFlatness(context, 0.1f);

            CGContextSetAlpha(context, self.lineAlpha);
            CGContextStrokePath(context); 
}

Regards
Ranjit.

This solved my issue, if anyone has the same issue, please implement this.