Re: drawRect runs twice, bounds are changed in between
Re: drawRect runs twice, bounds are changed in between
- Subject: Re: drawRect runs twice, bounds are changed in between
- From: N!K <email@hidden>
- Date: Sat, 17 Jan 2015 14:33:03 -0800
On Jan 16, 2015, at 5:30 AM, Uli Kusterer <email@hidden> wrote:
> On 15 Jan 2015, at 07:58, Quincey Morris <email@hidden> wrote:
>> Putting those two ideas together leads to a better approach. Create the bezier path once, relative to an arbitrary bounding rect — say 1000 x 1000. (But any rect would do.) When you need to draw the path, set the CTM of the context to scale 1000 x 1000 (the reference bounds) to the context’s width x height (the view bounds). Then just draw the original path and AppKit will scale the bezier path for you.
>
> That's not the be-all end-all, though. Scaling the CTM scales line widths and heights as well. So if you for example want to skew the path, you'd get lines that are wider than they are tall (kind of calligraphic). Also, changing the CTM means that mouse click coordinates will be in a different coordinate system then your drawing, so if you’re e.g. implementing a graphics editor, you'll have to manually translate the coordinates each time.
>
> A better idea might be to have a list of original objects and projected objects. The list of projected objects is generated by transforming the paths. Whenever your view's bounds change, you rebuild this list of projected objects from the originals (thus keeping rounding errors etc. to a minimum as they can't accumulate). The drawing code just draws this projected list.
>
> As I don't know where 'temp' comes from in N!K’s code,
NSBezierPath* temp; is in the list of declarations.
_path is created once, in -(id)initWithCoder:(NSCoder*)coder .
_path is scaled to the new size and assigned to temp each time drawRect is called. Thus, there is no error buildup.
> this may be what's already happening, in which case I find that a better approach than mangling the CTM if your interest is in having a shape drawn crisply in a window. If you're instead looking to scale a drawing (whether vector or otherwise), where you want lines to be skewed, then Quincy.s approach is preferrable.
>
> -- Uli
Nick
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