Re: Method for finding intersection points

If you just want to find the intersections, it's actually trivial to
implement. It seems Raphael implements this.
The hard part is to optimize path (= remove path segments that are painted
on both side), making paths impervious to winding rules and doing
operations like union and xor

On Wed, Jun 19, 2013 at 12:05 PM, Stephen Chenney <schenney@chromium.org>wrote:

> It's a very hard thing to implement correctly for all cases, and a call
> might be rather expensive. I worry that different implementations will give
> different answers under surprisingly simple situations.
>
> Still, I think we will reasonably soon have the ability to do this in the
> Chrome back-end (Skia) so for us it might be a fairly easy thing to
> implement.
>
> Thanks for providing motivation for the change.
>
> Stephen.
>
>
> On Wed, Jun 19, 2013 at 9:19 AM, Doug Schepers <schepers@w3.org> wrote:
>
>> Hi, Nikita-
>>
>> I strongly agree.
>>
>> In writing apps with SVG and JS, I've wanted to have an easy way to get
>> intersections for many different things. I'm currently using Kevin
>> Lindsey's intersection library on a personal project.
>>
>> I actually believe that we should work on a more comprehensive API for
>> point, vector, and matrix math (including intersections), which could be
>> used for both SVG and Canvas (and possibly CSS); JS libs like Sylvester [1]
>> and mjs [2] are a good start, but would have better performance if
>> implemented natively in browsers. I don't have the math skills to do this
>> myself, but if we could find someone to help spec it out, I could
>> facilitate the spec production.
>>
>> [1] http://sylvester.jcoglan.com/
>> [2] http://webgl-mjs.googlecode.**com/hg/docs/files/mjs-js.html<http://webgl-mjs.googlecode.com/hg/docs/files/mjs-js.html>
>>
>> Regards-
>> -Doug
>>
>>
>> On 6/19/13 6:27 AM, Nikita Vasilyev wrote:
>>
>>> I propose to implement a method for finding intersection points for
>>> basic shapes and paths.
>>>
>>> svgElements.**getIntersectionPoints( svgElement )
>>> -> Array of points, e.g. [{x: 1, y: 120}, …]
>>>
>>> There are JavaScript libraries for this
>>> http://www.kevlindev.com/**geometry/2D/intersections/<http://www.kevlindev.com/geometry/2D/intersections/>
>>> http://raphaeljs.com/**reference.html#Raphael.**pathIntersection<http://raphaeljs.com/reference.html#Raphael.pathIntersection>
>>>
>>> There is a getIntersectionList method which calculates intersection
>>> using bounding boxes of the elements
>>> (http://dev.w3.org/SVG/**profiles/1.1F2/publish/struct.**
>>> html#__svg__SVGSVGElement__**getIntersectionList<http://dev.w3.org/SVG/profiles/1.1F2/publish/struct.html#__svg__SVGSVGElement__getIntersectionList>
>>> )
>>> It does NOT return intersection points.
>>>
>>> Motivation
>>> Finding intersection is commonly used for drawing and prototyping
>>> applications such as Adobe Illustrator to "snap" objects.
>>>
>>
>>
>>
>>
>