[Fwd: Re: [mapserver-dev] Canvas support for MapServer]

[Jan Hartmann]

Another option would be to use GeoJSON. Is MapServer able to output

GeoJSON, or is it going to be? I guess it would be much easier to write 
a conversion program from GeoJSON to Canvas than from SVG, and I am sure 
it would be much more efficient.

Jan

Stephen Woodbridge wrote:
> Dan Little wrote:
>> I think there is some problems with the Canvas implementations across
>> the different browsers.  I've actually done quite a bit of work using
>> the Canvas and the exCanvas extension from Google.  While exCanvas
>> SAYS it is a 100% implementation for IE there tends to be a number of
>> quirks when it comes to actually placing objects in a drawing stack,
>> animating them, or simply clearing the canvas at a predictable point.
>>
>>
>> Also, I think it would be much more to the benefit to simply have a
>> VML output.  A little bit of browser sniffing is easy to do with any
>> JS application (or even some server side scripting) and you'd be
>> outputting either SVG or VML in that browser's native preferred
>> format.  No goofy javascript library required.
>
> I think converting some SVG into the proposed Canvas format would be a 
> good starting point so we can evaluate the performance. If consuming a 
> large Canvas file causes the browser to be slow or crash, then it 
> might not make sense to even consider moving forward with something 
> like this. It would seem to be a pretty straight forward task if we 
> can find someone that knows perl, Canvas and svg or is willing to do a 
> little research.
>
> -Steve W
>
>> ----- Original Message ----
>>> From: Brent Fraser <bfraser at geoanalytic.com> To: Jan Hartmann
>>> <j.l.h.hartmann at uva.nl> Cc: mapserver-dev at lists.osgeo.org Sent:
>>> Tuesday, January 27, 2009 9:07:32 AM Subject: Re: [mapserver-dev]
>>> Canvas support for MapServer
>>>
>>> Jan,
>>>
>>> So your thought is to have MapServer generate something like
>>> (hacked from the example on
>>> https://developer.mozilla.org/en/Canvas_tutorial/Basic_usage):
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> Sure, it could be done.  One way is to write another output driver
>>> for Mapserver.  Another is to use some server-side scripting to
>>> ingest Mapserver's SVG and change into JavaScript-canvas code like
>>> that above. A performance hit, but at least it would be on the
>>> server side, and it might be a good way to prototype the Mapserver
>>> driver.
>>>
>>> Brent
>>>
>>> Jan Hartmann wrote:
>>>> Hi Brent,
>>>>
>>>> First let me say that Canvas support is just an idea; I think it
>>>> can be done
>>> but whether it is advisable to do so is up to you to decide. I
>>> liked the idea because the Canvas element is supported nowadays by
>>> most browsers, unlike SVG which needs a plugin. It is also much
>>> simpler, so it's easier to use for simple maps, and especially for
>>> simple interactive operations like digitizing, or combining
>>> server-side with client-side graphics. That's why I would prefer 
>>> Canvas above SVG, let alone the fact that I much prefer to program
>>> in native Javascript above parsing XML. Most of my maps are simple
>>> (I would guess that goes for many people here), so SVG is decidedly
>>> overkill. The Canvas HTML element also fits nicely in the page
>>> layout and can be processed easily by web-editors.
>>>> Your suggestion that Canvas could be implemented at the client
>>>> side by
>>> catching SVG output and transforming it into Canvas directives is
>>> certainly viable. That is also Paul Spencer's view in his reply to
>>> my email.  Yet I would prefer a server-side approach: it's more
>>> efficient (no second parsing of SVG code that had to be generated
>>> in the first place), and I think the server-side code can be easily
>>> adapted from the SVG driver. Canvas is a very simple format, just a
>>> few graphic primitives, more like GD than SVG actually.
>>>> Again, I don't know how difficult it would be to add a Canvas
>>>> outputformat,
>>> and whether it fits at all into the MapServer design philosophy.
>>> However, when it could be done, it would give me an a far more
>>> easier tool than SVG  to combine server-side and client-side
>>> mapping.
>>>> Jan
>>>>
>>>> Brent Fraser wrote:
>>>>> Jan,
>>>>>
>>>>> My interest is in building a (or re-purposing an existing) tool
>>>>> for
>>> Cartographic Layout, for printing or rendering a graphics format
>>> for easy viewing (e.g. PDF).  Steve's comments were about using
>>> existing Web formats and syntax to describe the layout, and
>>> existing(?) web editors to do the placement/moving of the layout
>>> components.
>>>>> My (very limited) understanding of the HTML tag is that it's a
>>>>>
>>> "container" recognized by the browser, and vector (and raster)
>>> graphics are rendered into it using client-side JavaScript.  Sort
>>> of the JavaScript equivalent of the SVG format.
>>>>> It would be possible to add another output format to Mapserver
>>>>> to generate
>>> JavaScript code of canvas rendering methods, but a more elegant
>>> approach might be to write a small(?) JavaScript module to ingest
>>> Mapserver's SVG and render the objects to the canvas.
>>>>> Are there some specific features of the direct-canvas-output
>>>>> approach not
>>> available in SVG that you need?
>>>>> Brent Fraser
>>>>>
>>>>>
>>>>> Jan Hartmann wrote:
>>>>>> Hi folks,
>>>>>>
>>>>>> A few weeks ago I suggested in a thread about PDF support
>>>>>> that Mapserver
>>> could perhaps be made to support the new "Canvas" tag. There were
>>> no reactions to this, so I don't know if this suggestion is
>>> viable/advisable/practicable, or just downright stupid. Can anyone
>>> comment? (from 
>>> http://lists.osgeo.org/pipermail/mapserver-dev/2009-January/008055.html) 
>>>
>>>
>>>>>>> I am wondering if MapServer support for the "Canvas" tag
>>>>>>> could do what
>>> Steve suggests in a more simple way. Originally, only Safari, Opera
>>> and Firefox supported this tag to allow (simple) 2D drawing, but
>>> recently a surprisingly simple Javascript interface for IE has
>>> become available, translating Canvas command to native IE VRML
>>> commands. It requires just one single script tag in the web page.
>>>>>>> See the tutorial at the Mozilla site at:
>>> https://developer.mozilla.org/en/Canvas_tutorial
>>>>>>> and the IE interface (from the Google stables) at:
>>> http://excanvas.sourceforge.net/
>>>>>>> This is something I have long been looking for. The
>>>>>>> graphics are very
>>> simple, so the functionality is nothing like PDF or SVG, but I
>>> could imagine that a driver for MapServer could fulfill many needs.
>>> I can use it already by letting Mapserver generate raw coordinates
>>> and catching them with some sort of Ajax, but a separate driver
>>> would be very neat of course.
>>>>>>> How about it?
>>>>>>>
>>>>>>> Jan
>>>>>>>
>>>>>>>
>>>>>> ------------------------------------------------------------------------ 
>>>>>>
>>>>>>
>>>>>>
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>>
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