[mapguide-trac] #496: Fix inconsistent naming of units in stylization

[MapGuide Open Source]

#496: Fix inconsistent naming of units in stylization
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   Reporter:  waltweltonlair  |       Owner:  waltweltonlair
       Type:  task            |      Status:  new           
   Priority:  high            |   Milestone:  2.1           
  Component:  General         |     Version:  2.0.0         
   Severity:  minor           |    Keywords:                
External_id:                  |  
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 Stylization code uses terms like "pixels", screen units", and "rendering
 units" inconsistently, which leads to confusion when working with the
 code.  For example, the SE_Renderer class defines a virtual method named
 !GetPixelsPerMillimeterScreen.  This is supposed to return the number of
 native renderer units per millimeter in device space.  For some renderers
 (AGG, GD) the native units are indeed normal device pixels, but for other
 renderers (DWF) the native units are W2D units and not pixels.

 The SE_Renderer API also defines low level rendering methods:
 !DrawScreenPolyline, !DrawScreenText, etc.  These take native renderer
 units as arguments, and hence "screen units" are the native renderer
 units.

 The following changes need to be made:
  * code needs to be updated everywhere to use "screen units" when working
 with native renderer units
  * the word "pixel" should only be used when referring to actual physical
 pixels
  * !GetPixelsPerMillimeterScreen will be renamed to
 !GetScreenUnitsPerMillimeterDevice
  * !GetPixelsPerMillimeterWorld will be renamed to
 !GetScreenUnitsPerMillimeterWorld

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Ticket URL: <https://trac.osgeo.org/mapguide/ticket/496>
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