msClipPolygonRect() / msClipPolylineRect()

[Frank Warmerdam]

Folks,

As part of an optimization project, funded by the Department of
Fisheries and Oceans I am digging through a few things.  I found
that in my test rendering something 15% of my time was spent in
msClipPolygonRect() as part of normal rendering.

A quick review highlighted that many of the features being put
through clipping were completely within the clip rectangle, so alot
of work was being done to accomplish no change.  I have modified
msClipPolygonRect() and msClipPolylineRect() in 4.5 CVS to return
immediately if they determine that the bounds of the shape are
completely within the clip rectangle.

In my case this cut the clipping time by about 50%.

My only concern with this change is whether there is any risk of
shapeObj bounds not being correct.  Does anyone know of circumstances
when the bound might not be in sync with the actual contents of the
shape?

I have applied the same change to msClipPolygonRect() though I
don't use it much in my test case.

I suspect that there may be futher opportunities for optimization on
this function. For instance, it doesn't seem like there is any point
in computing intersects for line segments where both end points are
within the search rect.

Best regards,
--
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent