Question

I understand there is CGContextClearRect though that makes you clear everything inside the drawRect class.
How do i select one CGContextRef and clear that instead?
for my case my code goes:

//Put clearing syntax here
if(dp.gPoints == nil || dp.gPoints->size() < 1)
    return;
CGContextBeginPath(g);
vector<CGPoint>::iterator k = dp.gPoints->begin();
CGContextMoveToPoint(g, (*k).x, (*k).y);
++k;
while(k != dp.gPoints->end()){
    CGContextAddLineToPoint(g, (*k).x, (*k).y);
    ++k;
}
vector<CGPoint>::reverse_iterator L = dp.dPoints->rbegin();
while(L != dp.doodlePoints->rend()){
    CGContextAddLineToPoint(g, (*L).x, (*L).y);
    ++L;
}
//CGContextAddLineToPoint(g, (*k).x, (*k).y);
CGContextSetFillColor(g, CGColorGetComponents([[UIColor greenColor] CGColor]));
CGContextEOFillPath(g);

Answer 1

Replace these two lines:

CGContextSetFillColor(g, CGColorGetComponents([[UIColor greenColor] CGColor]));
CGContextEOFillPath(g);

with these lines:

CGContextSaveGState(g);
CGContextEOClip(g);
CGContextClearRect(g, rect);
CGContextRestoreGState(g);

assuming rect was the argument passed to your drawRect: method.