Custom view, drawRect, clip?

• Martin Custom view, drawRect, clip? Feb 04 2008, 19:45
  Hi,
  
  I have a custom view in which I do my drawing in the -(void)drawRect:
  (NSRect)rect method. For a start, I just want to draw a huge gradient
  in that view. So I just do:
  - (void)drawRect:(NSRect)rect {
  [fancyGradient drawInRect:rect angle:270.0];
  }
  
  But then, Cocoa needs to refresh some small parts of that view, so it
  calls drawRect: with rect being much smaller than the view's frame. If
  I keep the previous version of drawRect, the result produced is not
  what I want: since fancyGradient is computed for rect, with rect being
  smaller that my view's frame, a small gradient is overlayed on top of
  the big one.
  
  I have one solution for that problem :
  - (void)drawRect:(NSRect)rect {
  rect.origin.y = 0;
  rect.size.height = [self frame].size.height;
  [fancyGradient drawInRect:rect angle:270.0];
  }
  
  My first question is: is it bad to draw outside the initial rect?
  
  My second question is: should I create the gradient first, then clip
  it, then draw it? Can I clip NSGradient? (If no, do I have to use
  CGGradient and CoreGraphics instead ?)
  
  My third question is: I have the same problem with a NSBezierPath. How
  do I clip it? What does [myPath addClip] do (yes, I've read the doc,
  so my question is: is clipping path of the current graphic context
  automagically set to rect)? What is the difference with [NSBezierPath
  clipRect:rect]?
  
  Thanks,
  Martin.
• I. Savant Re: Custom view, drawRect, clip? Feb 04 2008, 19:54
  > - (void)drawRect:(NSRect)rect {
  > [fancyGradient drawInRect:rect angle:270.0];
  > }
  >
  > But then, Cocoa needs to refresh some small parts of that view, so it
  > calls drawRect: with rect being much smaller than the view's frame.
  

  
    The Cocoa Drawing Guide explains the reasons for this in great
  detail. The short version: Cocoa only asks you to draw what's "dirty".
  It's up to you to give your view intelligence enough to deal with
  drawing all or part of itself.
  
  

  > I have one solution for that problem :
  > - (void)drawRect:(NSRect)rect {
  > rect.origin.y = 0;
  > rect.size.height = [self frame].size.height;
  > [fancyGradient drawInRect:rect angle:270.0];
  > }
  >
  > My first question is: is it bad to draw outside the initial rect?
  

  
    Not at all, but there's an easier way:
  
  - (void)drawRect:(NSRect)rect
  {
    [fancyGradient drawInRect:[self bounds] angle:270.0];
  }
  
  

  > My second question is: should I create the gradient first, then clip
  > it, then draw it? Can I clip NSGradient? (If no, do I have to use
  > CGGradient and CoreGraphics instead ?)
  >
  > My third question is: I have the same problem with a NSBezierPath. How
  > do I clip it? What does [myPath addClip] do (yes, I've read the doc,
  > so my question is: is clipping path of the current graphic context
  > automagically set to rect)? What is the difference with [NSBezierPath
  > clipRect:rect]?
  

  
    Again, read the Cocoa Drawing Guide:
  
  http://developer.apple.com/documentation/Cocoa/Conceptual/CocoaDrawingGuide
  /GraphicsContexts/chapter_3_section_3.html#
  
    The above page covers this in detail.
  
  --
  I.S.
• Martin Re: Custom view, drawRect, clip? Feb 04 2008, 20:02
  > Again, read the Cocoa Drawing Guide:
  >
  > http://developer.apple.com/documentation/Cocoa/Conceptual/CocoaDrawingGuide
  /GraphicsContexts/chapter_3_section_3.html#
  >
  > The above page covers this in detail.
  

  
  Everything I need to know is indeed in that document.
  Thanks and sorry for not having read the doc more carefully.
  
  -Martin.
• I. Savant Re: Custom view, drawRect, clip? Feb 04 2008, 20:09
  > Everything I need to know is indeed in that document.
  > Thanks and sorry for not having read the doc more carefully.
  

  
    For what it's worth (and not to sound like a smart-a**), the page
  was found immediately by googling the phrase "cooca drawing clip" - it
  was the top result (above some links for hot cocoa and cookie clip
  art, apparently). I already knew the drawing guide would have the
  answer, though I haven't read it in awhile, but I didn't know where.
  Google knows, though.
  
    Then again, Google just sent me on a merry chase for a phantom
  restaurant that turned out to be a parking garage during lunch today
  ...
  
  --
  I.S.