[Mapserver-users] Color allocation in Mapserver 4.0 8bit mode, possible bug

[Steve Lime]

The issue is when colors are allocated. Old versions of MapServer
allocated all possible
colors (with the exceptions of rasters) as the mapfile was parsed and
stored colors
as index values. The new code uses RGB for colors instead and colors
are not allocated
until necessary. I'm talking with Frank about possible fixes, best of
old and new.

Steve

>>> Claude Philipona <claude-mapserver at skirando.ch> 09/23/03 01:12PM
>>>
Hello,

Migrating an application (http://map.epfl.ch) from 3.6 version to 4.0,
I
was to a different behaviour in colors allocation.

We have a several vector layers of colored polygons representing
buildings
and rooms, each buildings level stacking together with transperency. On
top
of that, there are several layers that should appear in gray/black.

With version 3.6, the image generated by mapserver didn't eat all the
256
colors of the colormap before the handling of labels (even with the all
the
colors generated by the multi levels transparency processing on the
layers), and the labels were properly rendered.

With version 4.0, the colors of the label changes evreytime you change
location/zoom, since all the 256 colors are eaten just by the
transparency
process. When the colors of the surroundings polygon are in the blue
shades, labels appears in blue, when in green, labels appear in
green,...

You can see the difference between these two images produced with the
exact
same mapfile:

mapserver 3.6:
http://www.camptocamp.com/~claude/mapserver/demo_mapserver_36.gif 
(notice label in black as it should be)

mapserver 4.0:
http://www.camptocamp.com/~claude/mapserver/demo_mapserver_40.gif 
(notice text in green, but wanted in black)

Why is the behaviouor different? Is it a bug?

With 4.0, I could use RBG output, but it is not quite appropriate for
this
kind of data: jpeg give poor images for a reasonable size and PNG24
are
double the size of gif or png8. So I really want to stick to 8bit
mode.

As there is no COLOR_MATCH_THRESHOLD for transparency processing on
vector
data, I'm using a workaournd for now:
I'm using a fake layer (hidden by other layer), as first layer
containing
polygons covering the whole extent, with colors set to populate right
at
the beginning the colors needed for labels and symbols. It works fine,
but
it is not a very nice way to handle this problem.

As this application is quite heavy (>10'000 line mapfile), it is a
good
test sample. During the migration, I discoverd several little problem,
I
will give reports to the list on each of these next few days.

Thanks,

Claude
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