Re: maintaining alpha value for intersecting lines?
Re: maintaining alpha value for intersecting lines?
- Subject: Re: maintaining alpha value for intersecting lines?
- From: Graham Cox <email@hidden>
- Date: Fri, 14 Sep 2012 09:24:04 +1000
On 14/09/2012, at 7:56 AM, Koen van der Drift <email@hidden> wrote:
>
> On Sep 13, 2012, at 1:01 PM, Andy Lee <email@hidden> wrote:
>
>>>
>>> Is that possible, since they all have different begin and end points?
>>
>> Yes. An NSBezierPath can contain multiple unconnected paths.
>
> This did the trick, I created all lines within the same NSBezierPath, and when they overlap, the color remained the same. No need to set any blending or composition modes. Saved me also a lot of creating NSBezierPath instances and drawing them one at a time.
Combining paths into a single NSBezierPath means those paths are treated as a single object for a drawing operation, and intersections are rendered accordingly. However, this behaviour doesn't come at no cost - the code has to find those intersections and deal with them by ensuring that the same pixels are not rendered twice. While usually faster than looping over separate paths, this intersection finding can potentially slows things down a lot.
--Graham
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