[mapserver-dev] GSoC UTFGrid Project

Daniel Morissette dmorissette at mapgears.com
Mon Jul 8 10:52:40 PDT 2013

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.  :-(

Daniel Morissette
Provider of Professional MapServer Support since 2000

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