[whatwg] بخصوص: isPointInPath v. set of pixels in canvas hit regions

رنا عبدالله wedyan6221 at yahoo.com
Sat Jul 7 09:03:06 PDT 2012

pls.dont send any msg to my adress

 من: Maciej Stachowiak <mjs at apple.com>
إلى: Tab Atkins Jr. <jackalmage at gmail.com> 
نسخة كربونية: whatwg at lists.whatwg.org; Edward O'Connor <eoconnor at apple.com> 
تاريخ الإرسال: الجمعة 6 يوليو، 2012‏ 10:26 م
الموضوع: Re: [whatwg] isPointInPath v. set of pixels in canvas hit regions

On Jul 5, 2012, at 11:28 PM, Tab Atkins Jr. <jackalmage at gmail.com> wrote:

> On Thu, Jul 5, 2012 at 1:05 PM, Edward O'Connor <eoconnor at apple.com> wrote:

>> As things currently stand in the spec, implementations basically need to

>> keep N+1 bitmaps per canvas, where N is the number of hit regions. I

>> doubt any implementors would be enthusiastic to implement hit regions

>> like this. From a WebKit perspective, we'd much prefer keeping a Path

>> for each hit region, and then simply using isPointInPath for hit

>> testing. This also implies that the current piggybacking of "Clear

>> regions that cover the pixels" in clearRect() could go away. Yay! :)


> Bog-standard hit-testing algorithms apply.  Keep a single extra canvas

> around, draw each region into it with a different color.  When you're

> hit-testing, just see what color that pixel is, and look up which

> region is associated with it.  This is extremely fast and simple to

> implement, and has all the right properties - the "topmost" region for

> a given pixel is the one returned.

It also doubles the memory cost of the canvas if you use hit regions, which is likely much more than path-based hit testing would cost.

- Maciej

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