Question

No doubt this might be a duplicate question but I am not able to get proper solution from any post here. So I am posting this as new post with a hope that I get some solution.

I my drawing app I want to give a feature of opacity for lines to be drawn.
But when I assign alpha to color, I am getting overlapped points in between the line.

Some where I found that drawing in two views solves this issue, but I was not able to understand the logic behind that.

I am using normal quartz 2d code to draw line on touch events.

Answer 1

Hie..

This is my final solution..
I am now drawing lines on drawRect event and drawing the entire line at a time as a path..
This creates opacity to retain and now no line caps drawn in between..

No doubt this is the trick that is working since I am drawing on every touch and this works..

- (void)drawRect:(CGRect)rect {
for (int j=0; j<[pathArray count]; j++) 
{
    context = UIGraphicsGetCurrentContext();
    NSMutableDictionary *tmp=[pathArray objectAtIndex:j];
    NSMutableArray *currentPath=[tmp objectForKey:@"path"];
    for (int i=0; i<[currentPath count]; i++) 
    {
        CGPoint mid1 = [[self midPoint:[currentPath objectAtIndex:i+1]  :[currentPath objectAtIndex:i]] CGPointValue]; 
        CGPoint mid2 = [[self midPoint:[currentPath objectAtIndex:i+2] :[currentPath objectAtIndex:i+1]] CGPointValue];
        CGContextMoveToPoint(context, mid1.x, mid1.y);
        CGContextAddQuadCurveToPoint(context, [[currentPath objectAtIndex:i+1] CGPointValue].x, [[currentPath objectAtIndex:i+1] CGPointValue].y, mid2.x, mid2.y); 
        CGContextSetShadow(context, CGSizeMake(-2, -2), 3);
        CGContextSetAlpha(context, [[tmp objectForKey: @"opacity"] floatValue]);    
        CGContextSetLineCap(context, kCGLineCapRound);
        CGContextSetStrokeColorWithColor(context,[[tmp objectForKey: @"Color"] CGColor]);               
        CGContextSetLineWidth(context, [[tmp objectForKey: @"width"] floatValue]);              
        i+=2;
    }   
    CGContextStrokePath(context);

}
}