[GRASS-dev] [GRASS GIS] #2009: thumbnails.py failure

GRASS GIS trac at osgeo.org
Wed Jun 19 04:14:30 PDT 2013

#2009: thumbnails.py failure
 Reporter:  neteler             |       Owner:  grass-dev@…              
     Type:  defect              |      Status:  new                      
 Priority:  normal              |   Milestone:  7.0.0                    
Component:  Compiling           |     Version:  svn-trunk                
 Keywords:  r.colors, v.colors  |    Platform:  All                      
      Cpu:  Unspecified         |  

Comment(by glynn):

 Replying to [comment:4 hamish]:

 > I note in trunk there is some rendering error in the top-left corners of
 all the image boxes, manifested as a missing pixel. (in GRASS 6 there
 was/is a similar bug in d.barscale + Xdriver)

 > Finally, this is a clear case where the Xdriver does a better job than
 the Cairo driver, compare the thumbnails in trunk with the crispness of
 the devbr6 versions:
 >   source:grass/branches/develbranch_6/raster/r.colors/thumbnails
 > ... sometimes you want 1px lines to be exactly 1px wide, and no anti-

 Both of these are a result of the d.* modules having been "minimally
 ported" from the 6.x display API.

 Closed paths should be closed with D_close() rather than by
 D_cont_{abs,rel} back to the starting point. The latter will result in the
 path being treated as open and thus having end caps.

 Single-pixel lines should be drawn along the centre-line of a pixel row or
 column, not along the boundary between rows/columns. IOW, the vertices
 should have coordinates which are offset from an integer value by 0.5,
 rather than being integers.

 The display API can't realistically do this automatically because it can't
 easily and reliably determine when it needs to "fix" the coordinates and
 when it should use them verbatim. E.g. d.vect shouldn't fix boundaries
 which happen to be axis-aligned rectangles because they'll be misaligned
 with the rest of the data.

 OTOH, if you have a 200-dpi display, single-pixel lines may as well just
 not be drawn, because you probably won't be able to see them. For a quick
 fix, setting the line width to 2 pixels is probably simpler than changing
 the coordinates.

Ticket URL: <https://trac.osgeo.org/grass/ticket/2009#comment:5>
GRASS GIS <http://grass.osgeo.org>

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