[GRASS-dev] [GRASS GIS] #2175: m.nviz.image: adding transparency_value= changes raster layer stacking order

[GRASS GIS]

#2175: m.nviz.image: adding transparency_value= changes raster layer stacking
order
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 Reporter:  hamish                      |       Owner:  grass-dev@…              
     Type:  defect                      |      Status:  new                      
 Priority:  normal                      |   Milestone:  6.4.4                    
Component:  Default                     |     Version:  svn-trunk                
 Keywords:  m.nviz.image, transparency  |    Platform:  Linux                    
      Cpu:  x86-64                      |  
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Comment(by hamish):

 Replying to [comment:1 annakrat]:
 > This is a duplicate of #2117. You get the same effect in `TclTk`
 > Nviz when you click on Draw button instead of Draw current. I
 > haven't looked into this yet what's the difference between those
 > two buttons.

 thanks. in tcl/tk nviz the 'Draw' button at the top re-renders the entire
 scene, i.e. all layers of all types. The 'Draw Current' button in the
 Raster Surfaces panel just renders the current raster layer (from the drop
 down list). So to produce the effect there I usually select the
 transparent planar surface, then click the main Clear and Draw buttons,
 then click the lower 'Draw current' button to overlay any planar surfaces,
 then take a screenshot.

 There seems to be a slight difference in behaviour between what Richard
 reported for wx #2117 and what happens from the command line: In #2117
 setting the transparency to 0 (i.e. opaque) had the rendering order go
 back to normal. On the command line that doesn't work, if you use the
 transparency_value= option at all (even with 0,0) the rendering order gets
 mixed up. In order to get a cutting plane effect from a constant surface
 you need to leave off the transparency_value= option altogether. I'd note
 that the tcl/tk NVIZ settings allow unset,0-255, with the default as
 unset. Perhaps unset != 0, and some test needs to be changed from
 if(unset) to if(unset || value == 0) ?


 Hamish

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Ticket URL: <https://trac.osgeo.org/grass/ticket/2175#comment:2>
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