[OpenLayers-Users] Towards an eraser tool in OpenLayers

[Dan Garland]

Thanks for your response Atle,

I'm trying to achieve a result that when I draw lots of lines on a page, 
that I can erase everything underneath a path, preserving the parts of 
the features not touched by the eraser. This isn't therefore a case of 
removing the entire feature (more of a 'hide' feature) but cutting out 
parts of the drawing. I've tried deleting points from the geometry, but 
found it imprecise and slow.

Thanks,
Dan

Atle Frenvik Sveen wrote:
> Hmm, I think your proposal looks overly complicated. Why don't just
> remove the feature from the layer it is drawn on? 
> 
> And possibly store it somewhere else if you want to regret the deletion?
> 
> Or am I misunderstanding you here?
> 
> -atle
> 
> On Wed, 2010-01-27 at 12:28 +0000, Dan Garland wrote:
>> Any takers? Or am I on the wrong track here?
>>
>> Thanks in advance,
>> Dan
>>
>> Dan Garland wrote:
>>> Hi all,
>>>
>>> I'm a Ruby on Rails developer working on my first project with 
>>> OpenLayers. I'm tasked with developing an free-hand eraser tool that can 
>>> erase features created by the drawFeatures tool. Amongst other things 
>>> we've tried, my thinking is moving towards creating a SVG mask, based on 
>>> the existing drawing tool, in which the 'erased' line is actually a 
>>> black line within a white, rectangular SVG mask, which when applied over 
>>> the top of the tile layer would mask any drawn features from underneath. 
>>> I anticipate something like this:
>>>
>>> <svg width="8cm" height="8cm" viewBox="0 0 800 800" version="1.1"
>>>       xmlns="http://www.w3.org/2000/svg" 
>>> xmlns:xlink="http://www.w3.org/1999/xlink">
>>>    <defs>
>>>      <mask id="Mask" maskUnits="userSpaceOnUse" x="0" y="0" width="3968" 
>>> height="2964">
>>>        <rect x="0" y="0" width="3968" height="2964" fill="white" />
>>>        <!-- The 'eraser' line -->
>>>        <polyline fill="none" stroke="black" stroke-width="25" 
>>> points="400,0 400,800" />
>>>      </mask>
>>>    </defs>
>>>
>>> <!-- Example drawn features -->
>>>
>>>    <polyline id="myline" points="0,0 800,800" fill="none" 
>>> stroke-opacity="1" stroke-width="25" stroke-linecap="round" 
>>> stroke-linejoin="round" stroke-dasharray="none"/>
>>>    <polyline id="myline2" points="0,100 800,100" fill="none" 
>>> stroke-opacity="1" stroke-width="25" stroke-linecap="round" 
>>> stroke-linejoin="round" stroke-dasharray="none"/>
>>>    <polyline id="myline3" points="0,400 800,400" fill="none" 
>>> stroke-opacity="1" stroke-width="25" stroke-linecap="round" 
>>> stroke-linejoin="round" stroke-dasharray="none"/>
>>>
>>>     <use xlink:href="#myline" stroke="red" mask="url(#Mask)" />
>>>     <use xlink:href="#myline2" stroke="red" mask="url(#Mask)" />
>>>     <use xlink:href="#myline3" stroke="red" mask="url(#Mask)" />
>>>
>>> </svg>
>>>
>>> The problems I face with this approach is knowing how best to manipulate 
>>> the existing SVG object being referenced by OpenLayers. I wonder whether 
>>> it is feasible in OpenLayers to develop a control based on the 
>>> drawFeature tool that
>>>
>>> 1) Adds the mask <defs> section to the SVG Root at startup
>>> 2) Creates polyline elements with the mask
>>> 3) Adds <use> elements for each element in the tile layer to connect the 
>>> id and the mask
>>>
>>> Before I dive in and spent hours in an unfamiliar area I wonder if any 
>>> OpenLayers developers have encountered this use case and have a better 
>>> solution, or can shed any light on this proposed approach.
>>>
>>> Best Regards,
>>> Dan Garland
>>>
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