Strange behavior with UIBezierPath addClip - objective-c

Question

I'm trying to learn CoreGraphics and I have encountered a strange behavior.
I draw a rectangle and in it I draw given amount of diamonds,the shapes can be drawn with different filling (empty, filled and with stripes) my draw rect function looks like this:
- (void)drawRect:(CGRect)rect
{
UIBezierPath* roundedRect = [UIBezierPath bezierPathWithRoundedRect:self.bounds cornerRadius:9.0];
//don't draw where the round corners "cut" the rectangle
[roundedRect addClip];
//set a white background
[[UIColor whiteColor] setFill];
UIRectFill(self.bounds);
//set a black frame
[[UIColor darkGrayColor] setStroke];
[roundedRect stroke];
self.shade = STRIPED;
self.color = [UIColor greenColor];
self.number = 3;
rectOffset = self.bounds.size.width / (self.number * 2);
[self drawDiamondNumberOfTimes:self.number startOrigin:self.bounds.origin];
}
drawDiamondNumberOfTimes:startOrigin: is a recursive function that calculates the rectangle in which the shape will be drawing and draw the diamond boundaries using stroke
- (void) drawDiamondNumberOfTimes:(int) p_times startOrigin:(CGPoint) p_origin
{
if( p_times > 0)
{
CGRect drawArea;
drawArea.origin = CGPointMake(p_origin.x + rectOffset-shapeSize.width/2, self.bounds.size.height/4);
drawArea.size = shapeSize;
UIBezierPath *diamond = [[UIBezierPath alloc] init];
[diamond moveToPoint:CGPointMake(drawArea.origin.x, drawArea.origin.y+ shapeSize.height/2)];
[diamond addLineToPoint:CGPointMake(drawArea.origin.x+shapeSize.width/2, drawArea.origin.y)];
[diamond addLineToPoint:CGPointMake(drawArea.origin.x+shapeSize.width, drawArea.origin.y+ shapeSize.height/2)];
[diamond addLineToPoint:CGPointMake(drawArea.origin.x+shapeSize.width/2, drawArea.origin.y+ shapeSize.height)];
[diamond closePath];
[self.color setStroke];
[diamond stroke];
[self drawShadeOfDraw:diamond atRect:drawArea];
drawArea.origin.x += rectOffset + shapeSize.width/2;
[self drawDiamondNumberOfTimes:p_times-1 startOrigin:drawArea.origin ];
}
}
drawShadeOfDraw:atRect: set the different filling, where the strange behavior occurs.
With empty and solid fills it works perfect but with stripes, if I write [p_symbol addClip] then I get always one diamond striped even if self.number is set to 2 or 3. Without [p_symbol addClip] I get the correct number of diamonds but, of course, the stripes are all over the rectangle, here is the code for drawShadeOfDraw:atRect:
- (void)drawShadeOfDraw:(UIBezierPath*)p_symbol atRect:(CGRect)p_drawArea
{
switch (self.shade)
{
case STRIPED:
{
[p_symbol addClip];
for( int y = p_drawArea.origin.y; y < p_drawArea.origin.y+ p_drawArea.size.height; y+= 6)
{
[p_symbol moveToPoint:CGPointMake(p_drawArea.origin.x, y)];
[p_symbol addLineToPoint:CGPointMake(p_drawArea.origin.x+shapeSize.width, y)];
[self.color setStroke];
[p_symbol stroke];
}
break;
}
case SOLID:
{
[self.color setFill];
[p_symbol fill];
break;
}
default:
{
break;
}
}
}
Here are some images:
What am I doing wrong?

Answer 1

Adding to the clip is semi-permanent. Once the clipping area has been "reduced", you can't grow it again, per se. You can only restore it to a previous state. To do that you call CGContextSaveGState() before setting up context state (including clipping), do some drawing with that state, and then call CGContextRestoreGState() afterward to restore the context state to what it was before.
So, I suggest that you bracket your two methods with calls to save and restore the context state. Use UIGraphicsGetCurrentContext() to get a reference to the current context.