AGG

[Peter Bruton]

Hello;

I have been experimenting with AGG in MapServer (CVS April 26/2007) using
various OUTPUTFORMATs and found the results inconsistent.  To experiment
with various OUTPUTFORMATs (DRIVERs and IMAGEMODEs), a series of mapfiles
were created that have a single line layer where all features are drawn as
black lines with a width of one pixel.  

DRIVER GD/GIF and IMAGEMODE PC256
The lines were rendered as expected.  I performed this test as a baseline.
http://dev.atlas.gc.ca/cgi-bin/mapserv_dev?map=/home/atlas/mapdata/english/pb_gd_gif_pc256.map&mode=map

DRIVER AGG/PC256 and IMAGEMODE RGBA
While anti-aliasing was present the pattern of the line was not consistent.
 Sometimes a solid line and other times there were gaps in the line.
http://dev.atlas.gc.ca/cgi-bin/mapserv_dev?map=/home/atlas/mapdata/english/pb_agg_pc_rgba.map&mode=map

DRIVER AGG/PNG and IMAGEMODE RGBA
While anti-aliasing was present, the lines were gray and not black.  In
addition the pattern of the line was not consistent.  Sometimes a solid line
and other times there were gaps in the line.
http://dev.atlas.gc.ca/cgi-bin/mapserv_dev?map=/home/atlas/mapdata/english/pb_agg_png_rgba.map&mode=map

DRIVER AGG/PNG24 and IMAGEMODE RGBA
While anti-aliasing was present, the lines were gray and not black.  In
addition the pattern of the line was not consistent.  Sometimes a solid line
and other times there were gaps in the line.
http://dev.atlas.gc.ca/cgi-bin/mapserv_dev?map=/home/atlas/mapdata/english/pb_agg_png24_rgba.map&mode=map

DRIVER AGG/JPG and IMAGEMODE RGBA
While this produced the best rendering of the line, the background was
pixelated around the line.  
http://dev.atlas.gc.ca/cgi-bin/mapserv_dev?map=/home/atlas/mapdata/english/pb_agg_jpg_rgba.map&mode=map

DRIVER AGG/GIF and IMAGEMODE RGBA
While anti-aliasing was present the pattern of the line was not consistent.
 Sometimes a solid line and other times there were gaps in the line.
http://dev.atlas.gc.ca/cgi-bin/mapserv_dev?map=/home/atlas/mapdata/english/pb_agg_gif_rgba.map&mode=map

It is not clear to me why gray and/or lines with inconsistent patterns were
returned.   Are the DRIVER/IMAGEMODE conbinations I am using not compatible
with one another?  Or am I missing something else.

The symbol definition I am using for the lines in the mapfiles is:

SYMBOL
   TYPE ELLIPSE
   NAME solidline
   POINTS
     1 1
   END
   FILLED true
END

Any insight to the problems I am having is appreciated.

Peter Bruton