From 2e2390d0534f765281f67bae9c619f220687244c Mon Sep 17 00:00:00 2001 From: Paul Davis Date: Mon, 22 Sep 2014 11:35:55 -0400 Subject: alter the way the border of Canvas::Rectangle is drawn to meet the intent that a single pixel border passes through the corner coordinates --- libs/canvas/rectangle.cc | 36 ++++++++++++++++++++++++------------ 1 file changed, 24 insertions(+), 12 deletions(-) (limited to 'libs/canvas/rectangle.cc') diff --git a/libs/canvas/rectangle.cc b/libs/canvas/rectangle.cc index 1b75584849..4afdfbacd4 100644 --- a/libs/canvas/rectangle.cc +++ b/libs/canvas/rectangle.cc @@ -88,36 +88,48 @@ Rectangle::render (Rect const & area, Cairo::RefPtr context) con setup_outline_context (context); - /* see the cairo FAQ on single pixel lines to see why we do - * the 0.5 pixel additions. - */ - if (_outline_what == What (LEFT|RIGHT|BOTTOM|TOP)) { context->rectangle (self.x0 + 0.5, self.y0 + 0.5, self.width() - 1.0, self.height() - 1.0); } else { + /* the goal here is that if the border is 1 pixel + * 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 + * 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. + * + * see the cairo FAQ on single pixel lines to see why we do + * the 0.5 pixel additions. + */ + if (_outline_what & LEFT) { - /* vertical line: move x-coordinate by 0.5 pixels */ - context->move_to (self.x0 + 0.5, self.y0); - context->line_to (self.x0 + 0.5, self.y1); + /* vertical line: move x-coordinate left by 0.5 pixels */ + context->move_to (self.x0 - 0.5, self.y0); + context->line_to (self.x0 - 0.5, self.y1); } if (_outline_what & TOP) { - /* horizontal line: move y-coordinate by 0.5 pixels */ - context->move_to (self.x0, self.y0 + 0.5); - context->line_to (self.x1, self.y0 + 0.5); + /* horizontal line: move y-coordinate up by 0.5 pixels */ + context->move_to (self.x0, self.y0 - 0.5); + context->line_to (self.x1, self.y0 - 0.5); } if (_outline_what & BOTTOM) { - /* horizontal line: move y-coordinate by 0.5 pixels */ + /* horizontal line: move y-coordinate up by 0.5 pixels */ context->move_to (self.x0, self.y1 - 0.5); context->line_to (self.x1, self.y1 - 0.5); } if (_outline_what & RIGHT) { - /* vertical line: move x-coordinate by 0.5 pixels */ + /* vertical line: move x-coordinate left by 0.5 pixels */ context->move_to (self.x1 - 0.5, self.y0); context->line_to (self.x1 - 0.5, self.y1); } -- cgit v1.2.3