Custom view, drawRect, clip?
-
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. -
> - (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. -
> 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. -
> 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.
