[mapguide-trac] #632: Polylines can disappear completely using AGG renderer

[MapGuide Open Source]

#632: Polylines can disappear completely using AGG renderer
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 Reporter:  jbirch             |         Owner:  tonyfang
     Type:  defect             |        Status:  closed  
 Priority:  medium             |     Milestone:          
Component:  Rendering Service  |       Version:  2.0.1   
 Severity:  major              |    Resolution:  fixed   
 Keywords:  agg, gd, renderer  |   External_id:  1161231 
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Changes (by tonyfang):

  * status:  assigned => closed
  * resolution:  => fixed

Comment:

 In AGGRenderer::DrawScreenPolyline, the outline renderer is used to draw
 the polylines if the line weight is thin (<= 3 pixels). For Parcels.sdf
 (from the Redding data set), it is 1 pixel. The outline renderer seems to
 be dropping vertices when they are overlapping -- thus the lines don't all
 get rendered when the polyline data is dense.

 I removed the outline renderer code in AGGRenderer::DrawScreenPolyline,
 forcing it to stroke the lines as polygons -- this is code path taken when
 the lines are thick (> 3 pixels). After doing so, all the dense lines are
 rendered, yielding the expected results.

 There is a performance penalty. With my debug MG server, using the outline
 renderer, it takes 2.39 sec to render (albeit with missing lines). Using
 the stroke as polygon code, it takes 3.407 sec to render.

 The user can get around this rendering slowness by using standard
 optimization techniques such as generalization and/or scale ranges. So
 this slowness will probably not affect our end users in general.



 http://trac.osgeo.org/mapguide/changeset/3454

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Ticket URL: <http://trac.osgeo.org/mapguide/ticket/632#comment:5>
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