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canvas LineSet: fix rendering to get coordinates precisely correct

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This commit is contained in:
Paul Davis 2023-06-15 20:08:35 -06:00
parent 1251b90b66
commit 248e37ac0c
1 changed files with 35 additions and 18 deletions
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53
libs/canvas/line_set.cc
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@ -18,6 +18,8 @@
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/ */
#include <cmath>
#include "canvas/line_set.h" #include "canvas/line_set.h"
using namespace std; using namespace std;
@ -55,19 +57,25 @@ LineSet::compute_bounding_box () const
if (_orientation == Horizontal) { if (_orientation == Horizontal) {
_bounding_box = Rect (0, /* x0 */ double y0 = _lines.front().pos - (_lines.front().width/2.0);
_lines.front().pos - (_lines.front().width/2.0), /* y0 */ double y1 = _lines.back().pos - (_lines.back().width/2.0);
_extent, /* x1 */
_lines.back().pos - (_lines.back().width/2.0) /* y1 */ if (fmod (_lines.front().width, 2.)) {
); y0 -= _lines.front().width * 0.5;
}
_bounding_box = Rect (0, y0, _extent, y1);
} else { } else {
_bounding_box = Rect (_lines.front().pos - _lines.front().width/2.0, /* x0 */ double x0 = _lines.front().pos - _lines.front().width/2.0;
0, /* y0 */ double x1 = _lines.back().pos + _lines.back().width/2.0;
_lines.back().pos + _lines.back().width/2.0, /* x1 */
_extent /* y1 */ if (fmod (_lines.front().width, 2.)) {
); x0 -= _lines.front().width * 0.5;
}
_bounding_box = Rect (x0, 0, x1, _extent);
} }
} }
@ -93,11 +101,19 @@ LineSet::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
for (auto const & l : _lines) { for (auto const & l : _lines) {
Rect self; Rect self;
const double shift = l.width * 0.5;
if (_orientation == Horizontal) { if (_orientation == Horizontal) {
self = item_to_window (Rect (0, l.pos - (l.width/2.0), _extent, l.pos + (l.width/2.0))); self = Rect (0, l.pos - (l.width/2.0), _extent, l.pos + (l.width/2.0));
if (fmod (l.width, 2.)) {
self.y0 -= shift;
}
} else { } else {
self = item_to_window (Rect (l.pos - (l.width/2.0), 0, l.pos + (l.width/2.0), _extent)); self = Rect (l.pos - (l.width/2.0), 0, l.pos + (l.width/2.0), _extent);
if (fmod (l.width, 2.)) {
self.x0 -= shift;
}
} }
Rect isect = self.intersection (area); Rect isect = self.intersection (area);
@ -114,16 +130,17 @@ LineSet::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
/* Not 100% sure that the computation of the invariant /* Not 100% sure that the computation of the invariant
* positions (y and x) below work correctly if the line width * positions (y and x) below work correctly if the line width
* is not 1.0, but visual inspection suggests it is OK. * is not 1.0, but visual inspection suggests it is OK.
* See Cairo FAQ on single pixel lines to understand why we add 0.5
*/ */
if (_orientation == Horizontal) { if (_orientation == Horizontal) {
double y = self.y0 + ((self.y1 - self.y0)/2.0); const double y = item_to_window (Duple (0, l.pos)).y;
context->move_to (intersection.x0, y); context->move_to (intersection.x0, y + shift);
context->line_to (intersection.x1, y); context->line_to (intersection.x1, y + shift);
} else { } else {
double x = self.x0 + ((self.x1 - self.x0)/2.0); const double x = item_to_window (Duple (l.pos, 0)).x;
context->move_to (x, intersection.y0); context->move_to (x + shift, intersection.y0);
context->line_to (x, intersection.y1); context->line_to (x + shift, intersection.y1);
} }
context->stroke (); context->stroke ();