[GRASS-dev] Re: [GRASS GIS] #259: wxGUI: visualization problems with multiple rasters and vectors. not stable bug...

[GRASS GIS]

#259: wxGUI: visualization problems with multiple rasters and vectors. not stable
bug...
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  Reporter:  giohappy  |       Owner:  grass-dev at lists.osgeo.org
      Type:  defect    |      Status:  closed                   
  Priority:  major     |   Milestone:  6.4.0                    
 Component:  wxGUI     |     Version:  svn-develbranch6         
Resolution:  fixed     |    Keywords:                           
  Platform:  Linux     |         Cpu:  x86-32                   
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Comment (by glynn):

 Replying to [comment:7 giohappy]:

 > IMHO a modern GIS should automatically manage the display of the layers
 as the user interact with the Layer Manager. For example, if a user add a
 layer, it should be automatically added to the Map, triggering the "draw"
 or the "re-render" action...

 The main issue here is that Tk doesn't support masked, true-colour images;
 it supports GIF (masked, 256 colours) or PPM (true-colour, no mask). So
 you can't take the approach that you would in a C program, i.e. load all
 of the layers, then just redraw whenever the layer stack changes.

 Instead, it has to store the layers as image files. Whenever the layer
 stack changes, it has to call an external program (g.pnmcomp) to compose
 the layers into a single image, which it then loads and displays.

 The end result is that changing the set of layers could realistically be a
 hundred times slower than the ideal case (storing the layers in video
 memory, and having the GPU compose them).

 So, automatic updates should probably be user-selectable.

-- 
Ticket URL: <http://trac.osgeo.org/grass/ticket/259#comment:10>
GRASS GIS <http://grass.osgeo.org>