Q119164: INFO: Use of Polygon() Versus PolyPolygon()

Article: Q119164
Product(s): Microsoft Windows Software Development Kit
Version(s): winnt:3.5,3.51
Operating System(s): 
Keyword(s): kb16bitonly kbOSWinNT350 kbOSWinNT351 kbSDKWin16
Last Modified: 12-MAY-2001

3.10 3.50
WINDOWS NT
kbgraphic

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The information in this article applies to:

- Microsoft Win32 Application Programming Interface (API) 
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SUMMARY
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Polygon() draws a polygon, while PolyPolygon() draws a series of polygons. Using
multiple calls to Polygon() can offer better performance than using a single
call to PolyPolygon(); this is because PolyPolygon() does not consider the
polygons to be independent, but considers them to be one polygon with multiple
disjointed edges. However, there are times when PolyPolygon() is preferable,
particularly if the number of polygons is small.

MORE INFORMATION
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PolyPolygon() batches polygons in a single call, so there is less call overhead
than there is for multiple calls to Polygon(). However, to perform one combined
fill, PolyPolygon() has to work with all the edges in all of the polygons
simultaneously, resulting in sorting overhead. The overhead involved in sorting
becomes quite expensive when there are a lot of polygons, causing a net loss of
performance in comparison to Polygon().

GDI batches multiple Polygon() calls to be more efficient. Setting the batch
limit higher than the default of 10 with GdiSetBatchLimit() improves performance
even further. GDI and some drivers optimize convex polygons, but will only
optimize a single polygon drawn with either Polygon() or PolyPolygon().

Because PolyPolygon() treats all edges as part of one big polygon, it also draws
every pixel to be filled exactly once; this may be a performance advantage if a
lot of overlapping polygons are drawn, because Polygon() draws every pixel in
each polygon only once, even where there is an overlap.

PolyPolygon() considers all the polygons when applying the current fill mode, as
set by calling SetPolyFillMode(). Consequently, if any polygons overlap, the
result of one PolyPolygon() call may be different than the result of the
equivalent multiple Polygon() calls. If the polygons overlap and the raster
operation takes the destination pixel values into account, or if you want the
fill rule to be applied to overlapping areas, then it is preferable to use
PolyPolygon().

Additional query words: 3.10

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Keywords          : kb16bitonly kbOSWinNT350 kbOSWinNT351 kbSDKWin16 
Technology        : kbAudDeveloper kbWin32sSearch kbWin32API
Version           : winnt:3.5,3.51
Issue type        : kbinfo

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