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alter the way the border of Canvas::Rectangle is drawn to meet the intent that a single pixel border passes through the corner coordinates

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This commit is contained in:
Paul Davis 2014-09-22 11:35:55 -04:00
parent 45fd3593eb
commit 2e2390d053
1 changed files with 24 additions and 12 deletions
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36
libs/canvas/rectangle.cc
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@ -88,36 +88,48 @@ Rectangle::render (Rect const & area, Cairo::RefPtr<Cairo::Context> 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);
}