[mapguide-trac] #754: Polygon features are drawn wrong when not completely in the window

[MapGuide Open Source]

#754: Polygon features are drawn wrong when not completely in the window
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 Reporter:  waltweltonlair  |         Owner:  waltweltonlair
     Type:  defect          |        Status:  closed        
 Priority:  high            |     Milestone:  2.1           
Component:  General         |       Version:  2.0.2         
 Severity:  minor           |    Resolution:  fixed         
 Keywords:                  |   External_id:  1102648.01    
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Comment (by waltweltonlair):

 Since MapGuide 1.0, feature data has been clipped to the edge of the
 screen and the pseudo-edges have been displayed.  Only recently did we
 receive this request to not display these pseudo edges.

 As I explained above, we're dealing with two types of quirks: 1) the case
 where a polyline segment is clipped and not drawn, when in fact it should
 still be drawn (say because the line style has thickness); 2) the case
 where a clipped polygon segment (a pseudo edge) is drawn, when in fact it
 should not be drawn

 The fix for the first quirk is to expand the clip region by an amount
 corresponding to the "thickness" of the style being applied.  This ensures
 we don't clip away any feature geometry that would otherwise still be
 graphically visible inside the display area due to the style's
 "thickness".  This applies to both polylines and polygon edges.

 For the second quirk, one way to fix this is to not draw the pseudo-edges
 that get inserted when we clip polygons.  But the fix for the first quirk
 also happens to address the second quirk.  The pseudo-edges are currently
 still being rendered, but because we've expanded the clip region those
 pseudo-edges are now offscreen far enough so that they won't be
 graphically visible inside the display.

 So given that the graphical result should now be correct, I don't see any
 value in doing more work around this.  In fact, if we add code to filter
 out the rendering of pseudo-edges then the stylization / rendering
 performance will almost certainly decrease somewhat.

 The issue you describe with the status bar is a separate AJAX bug, and has
 nothing to do with the clipping / rendering work done in this submission.
 The AJAX viewer needs to account for the status bar and properly size /
 position the mapframe.

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Ticket URL: <http://trac.osgeo.org/mapguide/ticket/754#comment:5>
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