1 files changed, 222 insertions, 0 deletions
diff --git a/src/line-geometry.cpp b/src/line-geometry.cpp
new file mode 100644
index 0000000..1951bd5
--- /dev/null
+++ b/src/line-geometry.cpp
@@ -0,0 +1,222 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Routines for dealing with lines (intersections, etc.)
+ *
+ * Authors:
+ *   Maximilian Albert <Anhalter42@gmx.de>
+ *
+ * Copyright (C) 2007 authors
+ *
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#include "line-geometry.h"
+#include "desktop.h"
+#include "desktop-style.h"
+
+#include "display/sp-canvas.h"
+#include "display/sp-ctrlline.h"
+#include "display/sodipodi-ctrl.h"
+#include "ui/control-manager.h"
+
+using Inkscape::ControlManager;
+
+namespace Box3D {
+
+/** 
+ * Draw a line beginning at 'start'. If is_endpoint is true, use 'vec' as the endpoint
+ * of the segment. Otherwise interpret it as the direction of the line.
+ * FIXME: Think of a better way to distinguish between the two constructors of lines.
+ */
+Line::Line(Geom::Point const &start, Geom::Point const &vec, bool is_endpoint):
+    pt(start)
+{
+    if (is_endpoint)
+        v_dir = vec - start;
+    else
+    	v_dir = vec;
+    normal = v_dir.ccw();
+    d0 = Geom::dot(normal, pt);
+}
+
+Line::Line(Line const &line)
+= default;
+
+Line &Line::operator=(Line const &line) = default;
+
+boost::optional<Geom::Point> Line::intersect(Line const &line) {
+    Geom::Coord denom = Geom::dot(v_dir, line.normal);
+    boost::optional<Geom::Point> no_point;
+    if (fabs(denom) < 1e-6)
+        return no_point;
+
+    Geom::Coord lambda = (line.d0 - Geom::dot(pt, line.normal)) / denom;
+    return pt + lambda * v_dir;
+}
+
+void Line::set_direction(Geom::Point const &dir)
+{
+    v_dir = dir;
+    normal = v_dir.ccw();
+    d0 = Geom::dot(normal, pt);
+}
+
+Geom::Point Line::closest_to(Geom::Point const &pt)
+{
+	/* return the intersection of this line with a perpendicular line passing through pt */ 
+    boost::optional<Geom::Point> result = this->intersect(Line(pt, (this->v_dir).ccw(), false));
+    g_return_val_if_fail (result, Geom::Point (0.0, 0.0));
+    return *result;
+}
+
+double Line::lambda (Geom::Point const pt)
+{
+    double sign = (Geom::dot (pt - this->pt, this->v_dir) > 0) ? 1.0 : -1.0;
+    double lambda = sign * Geom::L2 (pt - this->pt);
+    // FIXME: It may speed things up (but how much?) if we assume that
+    //        pt lies on the line and thus skip the following test
+    Geom::Point test = point_from_lambda (lambda);
+    if (!pts_coincide (pt, test)) {
+        g_warning ("Point does not lie on line.\n");
+        return 0;
+    }
+    return lambda;
+}
+
+/* The coordinates of w with respect to the basis {v1, v2} */
+std::pair<double, double> coordinates (Geom::Point const &v1, Geom::Point const &v2, Geom::Point const &w)
+{
+    double det = determinant (v1, v2);;
+    if (fabs (det) < epsilon) {
+        // vectors are not linearly independent; we indicate this in the return value(s)
+        return std::make_pair (HUGE_VAL, HUGE_VAL);
+    }
+
+    double lambda1 = determinant (w, v2) / det;
+    double lambda2 = determinant (v1, w) / det;
+    return std::make_pair (lambda1, lambda2);
+}
+
+/* whether w lies inside the sector spanned by v1 and v2 */
+bool lies_in_sector (Geom::Point const &v1, Geom::Point const &v2, Geom::Point const &w)
+{
+    std::pair<double, double> coords = coordinates (v1, v2, w);
+    if (coords.first == HUGE_VAL) {
+        // catch the case that the vectors are not linearly independent
+        // FIXME: Can we assume that it's safe to return true if the vectors point in different directions?
+        return (Geom::dot (v1, v2) < 0);
+    }
+    return (coords.first >= 0 && coords.second >= 0);
+}
+
+bool lies_in_quadrangle (Geom::Point const &A, Geom::Point const &B, Geom::Point const &C, Geom::Point const &D, Geom::Point const &pt)
+{
+    return (lies_in_sector (D - A, B - A, pt - A) && lies_in_sector (D - C, B - C, pt - C));
+}
+
+static double pos_angle (Geom::Point v, Geom::Point w)
+{
+    return fabs (Geom::atan2 (v) - Geom::atan2 (w));
+}
+
+/*
+ * Returns the two corners of the quadrangle A, B, C, D spanning the edge that is hit by a semiline
+ * starting at pt and going into direction dir.
+ * If none of the sides is hit, it returns a pair containing two identical points.
+ */
+std::pair<Geom::Point, Geom::Point>
+side_of_intersection (Geom::Point const &A, Geom::Point const &B, Geom::Point const &C, Geom::Point const &D,
+                      Geom::Point const &pt, Geom::Point const &dir)
+{
+    Geom::Point dir_A (A - pt);
+    Geom::Point dir_B (B - pt);
+    Geom::Point dir_C (C - pt);
+    Geom::Point dir_D (D - pt);
+
+    std::pair<Geom::Point, Geom::Point> result;
+    double angle = -1;
+    double tmp_angle;
+
+    if (lies_in_sector (dir_A, dir_B, dir)) {
+        result = std::make_pair (A, B);
+        angle = pos_angle (dir_A, dir_B);
+    }
+    if (lies_in_sector (dir_B, dir_C, dir)) {
+        tmp_angle = pos_angle (dir_B, dir_C);
+        if (tmp_angle > angle) {
+            angle = tmp_angle;
+            result = std::make_pair (B, C);
+        }
+    }
+    if (lies_in_sector (dir_C, dir_D, dir)) {
+        tmp_angle = pos_angle (dir_C, dir_D);
+        if (tmp_angle > angle) {
+            angle = tmp_angle;
+            result = std::make_pair (C, D);
+        }
+    }
+    if (lies_in_sector (dir_D, dir_A, dir)) {
+        tmp_angle = pos_angle (dir_D, dir_A);
+        if (tmp_angle > angle) {
+            angle = tmp_angle;
+            result = std::make_pair (D, A);
+        }
+    }
+    if (angle == -1) {
+        // no intersection found; return a pair containing two identical points
+        return std::make_pair (A, A);
+    } else {
+        return result;
+    }
+}
+
+boost::optional<Geom::Point> Line::intersection_with_viewbox (SPDesktop *desktop)
+{
+    Geom::Rect vb = desktop->get_display_area();
+    /* remaining viewbox corners */
+    Geom::Point ul (vb.min()[Geom::X], vb.max()[Geom::Y]);
+    Geom::Point lr (vb.max()[Geom::X], vb.min()[Geom::Y]);
+
+    std::pair <Geom::Point, Geom::Point> e = side_of_intersection (vb.min(), lr, vb.max(), ul, this->pt, this->v_dir);
+    if (e.first == e.second) {
+        // perspective line lies outside the canvas
+        return boost::optional<Geom::Point>();
+    }
+
+    Line line (e.first, e.second);
+    return this->intersect (line);
+}
+
+void create_canvas_point(Geom::Point const &pos, unsigned int size, guint32 rgba)
+{
+    SPDesktop *desktop = SP_ACTIVE_DESKTOP;
+    SPCanvasItem * canvas_pt = sp_canvas_item_new(desktop->getControls(), SP_TYPE_CTRL,
+                          "size", size,
+                          "filled", 1,
+                          "fill_color", rgba,
+                          "stroked", 1,
+                          "stroke_color", 0x000000ff,
+                          NULL);
+    SP_CTRL(canvas_pt)->moveto(pos);
+}
+
+void create_canvas_line(Geom::Point const &p1, Geom::Point const &p2, guint32 rgba)
+{
+    SPDesktop *desktop = SP_ACTIVE_DESKTOP;
+    SPCtrlLine *line = ControlManager::getManager().createControlLine(desktop->getControls(), p1, p2);
+    line->setRgba32(rgba);
+    sp_canvas_item_show(line);
+}
+
+} // namespace Box3D 
+ 
+/*
+  Local Variables:
+  mode:c++
+  c-file-style:"stroustrup"
+  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
+  indent-tabs-mode:nil
+  fill-column:99
+  End:
+*/
+// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:fileencoding=utf-8:textwidth=99 :