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Add workaround to clipper zero-height path bug

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This commit is contained in:
jaseg 2021-02-06 14:59:44 +01:00
parent 13cb49b218
commit 3e323c953c
4 changed files with 67 additions and 14 deletions
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39
svg-flatten/src/svg_path.cpp
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@ -32,13 +32,14 @@ static void clipper_add_cairo_path(cairo_t *cr, ClipperLib::Clipper &c, bool clo
c.AddPaths(in_poly, ClipperLib::ptSubject, closed);
}
static void path_to_clipper_via_cairo(cairo_t *cr, ClipperLib::Clipper &c, const pugi::char_t *path_data) {
static bool path_to_clipper_via_cairo(cairo_t *cr, ClipperLib::Clipper &c, const pugi::char_t *path_data) {
istringstream d(path_data);
string cmd;
double x, y, c1x, c1y, c2x, c2y;
bool first = true;
bool has_closed = false;
bool path_is_empty = true;
while (!d.eof()) {
d >> cmd;
@ -48,6 +49,7 @@ static void path_to_clipper_via_cairo(cairo_t *cr, ClipperLib::Clipper &c, const
if (cmd == "Z") { /* Close path */
cairo_close_path(cr);
clipper_add_cairo_path(cr, c, /* closed= */ true);
has_closed = true;
cairo_new_path(cr);
path_is_empty = true;
@ -61,8 +63,9 @@ static void path_to_clipper_via_cairo(cairo_t *cr, ClipperLib::Clipper &c, const
*/
cairo_user_to_device(cr, &x, &y);
assert (!d.fail());
if (!first)
if (!first) {
clipper_add_cairo_path(cr, c, /* closed= */ false);
}
cairo_new_path (cr);
path_is_empty = true;
cairo_move_to(cr, x, y);
@ -93,6 +96,8 @@ static void path_to_clipper_via_cairo(cairo_t *cr, ClipperLib::Clipper &c, const
cairo_close_path(cr);
clipper_add_cairo_path(cr, c, /* closed= */ false);
}
return has_closed;
}
void gerbolyze::load_svg_path(cairo_t *cr, const pugi::xml_node &node, ClipperLib::PolyTree &ptree) {
@ -107,9 +112,33 @@ void gerbolyze::load_svg_path(cairo_t *cr, const pugi::xml_node &node, ClipperLi
ClipperLib::Clipper c;
c.StrictlySimple(true);
path_to_clipper_via_cairo(cr, c, path_data);
/* We canont clip the polygon here since that would produce incorrect results for our stroke. */
c.Execute(ClipperLib::ctUnion, ptree, fill_rule, ClipperLib::pftNonZero);
bool has_closed = path_to_clipper_via_cairo(cr, c, path_data);
if (!has_closed) {
/* FIXME: Workaround!
*
* When we render silkscreen layers from gerbv's output, we get a lot of two-point paths (lines). Many of these are
* horizontal. Now, clipper seems to have a bug (probably related to its scan-line algorithm) that makes it
* misbehave here:
*
* It seems that when the input paths are all perfectly colinear and horizontal, so that the resulting bounding box
* has zero height, clipper doesn't output anything. At least for open input paths.
*
* Since there is no way to get paths out of a Clipper once they're Add'ed, we work around this by just doing an
* intersection with a maximum-size rectangle instead, that seems to work.
*
* TODO: Fix clipper instead.
*/
auto le_min = -ClipperLib::loRange;
auto le_max = ClipperLib::hiRange;
ClipperLib::Path p = {{le_min, le_min}, {le_max, le_min}, {le_max, le_max}, {le_min, le_max}};
c.AddPath(p, ClipperLib::ptClip, /* closed= */ true);
c.Execute(ClipperLib::ctIntersection, ptree, fill_rule, ClipperLib::pftNonZero);
} else {
/* We cannot clip the polygon here since that would produce incorrect results for our stroke. */
c.Execute(ClipperLib::ctUnion, ptree, fill_rule, ClipperLib::pftNonZero);
}
}
void gerbolyze::parse_dasharray(const pugi::xml_node &node, vector<double> &out) {