[OSM-dev] Experiment: AJAX and <canvas> based online editor

[Nick Whitelegg]

As part of my investigations into online editor options I am experimenting 
with an AJAX and <canvas> tag based solution to see if it gives improved 
performance (compared to the applet).

I'm not so sure right now. If you go to

http://www.free-map.org.uk/osmajax/

you can see a demo. Wait until the data has been downloaded then try moving 
using the buttons. Drawing the nodes, segments and ways becomes progressively 
slower as more data gets loaded in - it thus seems the rate determining step 
is less the rendering but more looping through the nodes, segments and ways. 
This is on a fast machine (Linux, Firefox 1.5, 1gb ram, 3GHz)

However - given a screen covers 5km x 5km, it may be suitable for editing 
tasks such as creating new ways and editing the tags of the existing ways. On 
the other hand, maybe it's worth just updating the applet, in view of the 
less-than-great performance. An AJAX-based solution would have advantages 
such as easy integration with the rest of the web page (HTML-based tag 
editing facilities could easily be used for example).

On the other hand, does anyone have any general tips on improving drawing 
performance? This also applies to osmeditor2 which is also rather slow when 
drawing data - even though it does not attempt to draw things outside the 
current viewing area. The algorithm at present is more or less:

loop through nodes
    if node is in current viewing area, draw it
end

loop through ways
    loop through segments in way
         if node1 or node2 in view
              draw segment
         end if
    end
end

Nick