[mapserver-dev] GSoC UTFGrid Project

thomas bonfort thomas.bonfort at gmail.com
Mon Jul 8 10:55:57 PDT 2013

On 8 July 2013 19:52, Daniel Morissette <dmorissette at mapgears.com> wrote:
> On 13-07-08 1:36 PM, thomas bonfort wrote:
>> Yes, I don't think you can cut on that. The existing agg renderer uses
>> an 8bit RGBA buffer whereas you'll be writing to a single band 32bit
>> one (to encode the ids). You might be tempted to hack the current one
>> so that ids are encoded as an rgba quadruplet (as both are 32bits
>> wide) but that's probably asking for failure in the long run (You'll
>> have to rewrite most of the code anyway as you need to turn off
>> antialiasing).
> Encoding the 32 bits ids as rgba quadruplet is exactly what we were planning
> on doing. With respect to disabling antialiasing, I would have thought that
> this could have been handled by adding a few if statements here and there in
> mapagg.cpp, controlled by an outputformat option that the utfgrid renderer
> would have passed to the agg renderer at creation time to disable
> antialiasing.
> I have to admit that I had not looked deeply enough into the mapagg.cpp code
> to confirm the feasibility of all this. At least François' first
> implementation using this approach did work without too much impact on
> mapagg.cpp unless I'm mistaked. If you tell us that this approach could
> become a maintenance nightmare in the long run then we'll look for
> alternatives, but I hate to think that we'll be duplicating AGG rendering
> calls in order to produce a second class renderer to maintain with limited
> features.  :-(

A *very strong* +1 at writing your own agg code. There is going to be
so very little overlap between the rgba and int32 renderers that it's
not worth going into the pain of making mapagg.cpp do both.


> --
> Daniel Morissette
> http://www.mapgears.com/
> Provider of Professional MapServer Support since 2000
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