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comment fix and expansion re: Canvas::Rectangle outline

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Paul Davis 2014-10-30 09:05:27 -04:00
parent f7ce57e5b2
commit a942493565
1 changed files with 3 additions and 2 deletions
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libs/canvas/rectangle.cc
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@ -98,13 +98,14 @@ Rectangle::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) con
* thick, it will precisely align with the corner
* coordinates of the rectangle. So if the rectangle
* has a left edge at 0 and a right edge at 10, then
* the right edge must span -0.5..+0.5, the left edge
* the left edge must span -0.5..+0.5, the right edge
* must span 9.5..10.5 (i.e. the single full color
* pixel is precisely aligned with 0 and 10
* respectively).
*
* we have to shift left/up in all cases, which means
* subtraction along both axes.
* subtraction along both axes (i.e. edge at
* N, outline must start at N-0.5).
*
* see the cairo FAQ on single pixel lines to see why we do
* the 0.5 pixel additions.