gistfile1.m

- (void)drawRect:(CGRect)rect
{
	[super drawRect:rect];
	
	CGRect lastLineFragmentRect = CGRectZero;
	CGFloat lastBaselineOrigin = 0;
	
	CGFloat lineY = 0;
	CGFloat lineHeight = 0;
	
	for (NSInteger i=0; i<self.text.length; i++)
	{
		NSUInteger glyphIndex = [self.layoutManager glyphIndexForCharacterAtIndex:i];
		
		CGRect lineFragmentRect = [self.layoutManager lineFragmentRectForGlyphAtIndex:glyphIndex effectiveRange:NULL];
		lineFragmentRect.origin.y += self.textContainerInset.top;
		lineFragmentRect.origin.x += self.textContainerInset.left;
		
		if (CGRectEqualToRect(lineFragmentRect, lastLineFragmentRect))
		{
			continue;
		}
		
		CGFloat baselineOrigin = CGRectGetMaxY(lineFragmentRect)+self.font.descender;
		
		if (baselineOrigin != lastBaselineOrigin)
		{
			if (lineY)
			{
				lineHeight = baselineOrigin - lastBaselineOrigin;
				break;
			}
			else
			{
				lineY = baselineOrigin;
			}
		}
		
		lastLineFragmentRect = lineFragmentRect;
		lastBaselineOrigin = baselineOrigin;
	}

	
	if (!lineHeight)
	{
		lineHeight = self.font.lineHeight;
	}
	
	if (!lineY)
	{
		lineY = self.textContainerInset.top + self.font.ascender;
	}
	
	// draw lines in dirty area

	CGContextRef context = UIGraphicsGetCurrentContext();
	CGContextSetStrokeColorWithColor(context, [UIColor colorWithRed:0.0f green:0.0f blue:0.0f alpha:0.2f].CGColor);
	CGContextSetLineWidth(context, 1.0f);
	
	CGContextBeginPath(context);
	
	while (lineY < CGRectGetMaxY(rect))
	{
		if (lineY< CGRectGetMinX(rect))
		{
			// optimize, this line is not visible
			continue;
		}
		
		CGContextMoveToPoint(context, self.bounds.origin.x, lineY);
		CGContextAddLineToPoint(context, self.bounds.size.width, lineY);

		lineY += lineHeight;
	}
	
	CGContextClosePath(context);
	CGContextStrokePath(context);
}