make PolyLine use distance_to_segment_squared(), and add separate (null, for now) method Curve::covers(Duple) because the math there needs to be different, maybe

libs/canvas/canvas/curve.h

@@ -32,6 +32,8 @@ public:
     void render (Rect const & area, Cairo::RefPtr<Cairo::Context>) const;
     void set (Points const &);
 
+    bool covers (Duple const &) const;
+
   protected:
     void render_path (Rect const &, Cairo::RefPtr<Cairo::Context>) const;
     void render_curve (Rect const &, Cairo::RefPtr<Cairo::Context>) const;

libs/canvas/curve.cc

@@ -103,6 +103,8 @@ Curve::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
 void 
 Curve::render_path (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
 {
+	std::cerr << whatami() << '/' << name << " render curve w/" << _points.size() << " points, " << first_control_points.size() << " first and "
+		  << second_control_points.size() << " second\n";
 	PolyItem::render_curve (area, context, first_control_points, second_control_points);
 }
 
@@ -209,3 +211,9 @@ Curve::solve (std::vector<double> const & rhs)
 	
 	return x;
 }
+
+bool
+Curve::covers (Duple const & point) const
+{
+	return false;
+}

libs/canvas/lookup_table.cc

@@ -64,6 +64,7 @@ DumbLookupTable::items_at_point (Duple point) const
 		}
 		
 		if ((*i)->covers (point)) {
+			std::cerr << "\t\t" << (*i)->whatami() << '/' << (*i)->name << " covers " << point << std::endl;
 			vitems.push_back (*i);
 		}
 	}

libs/canvas/poly_item.cc

@@ -94,7 +94,13 @@ PolyItem::render_curve (Rect const & area, Cairo::RefPtr<Cairo::Context> context
 
 	for (Points::const_iterator i = _points.begin(); i != _points.end(); ++i) {
 
-		if (done_first) {
+		if (!done_first) {
+
+			Duple c = item_to_window (Duple (i->x, i->y));
+			context->move_to (c.x, c.y);
+			done_first = true;
+
+		} else {
 
 			Duple c1 = item_to_window (Duple (cp1->x, cp1->y));
 			Duple c2 = item_to_window (Duple (cp2->x, cp2->y));
@@ -104,12 +110,6 @@ PolyItem::render_curve (Rect const & area, Cairo::RefPtr<Cairo::Context> context
 
 			cp1++;
 			cp2++;
-			
-		} else {
-
-			Duple c = item_to_window (Duple (i->x, i->y));
-			context->move_to (c.x, c.y);
-			done_first = true;
 		}
 	}
 }

libs/canvas/poly_line.cc

@@ -17,7 +17,11 @@
     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
 
+#include <algorithm>
+
 #include "canvas/poly_line.h"
+#include "canvas/canvas.h"
+#include "canvas/utils.h"
 
 using namespace ArdourCanvas;
 
@@ -54,19 +58,37 @@ PolyLine::covers (Duple const & point) const
 
 	/* repeat for each line segment */
 
+	const Rect visible (_canvas->visible_area());
+	static const double threshold = 2.0;
+
 	for (i = 1, j = 0; i < npoints; ++i, ++j) {
 
-		/* compute area of triangle computed by the two line points and the one
+		Duple at;
-		   we are being asked about. If zero (within a given tolerance), the
+		double t;
-		   points are co-linear and the argument is on the line.
+		Duple a (_points[j]);
+		Duple b (_points[i]);
+		
+		/*
+		  Clamp the line endpoints to the visible area of the canvas. If we do
+		  not do this, we may have a line segment extending to COORD_MAX and our
+		  math goes wrong.
 		*/
 		
-		double area = fabs (_points[j].x * (_points[j].y - p.y)) + 
+		a.x = std::min (a.x, visible.x1);
-  			           (_points[i].x * (p.y - _points[j].y)) + 
+		a.y = std::min (a.y, visible.y1);
-			           (p.x * (_points[j].y - _points[i].y));
+		b.x = std::min (b.x, visible.x1);
-		if (area < 0.001) {
+		b.y = std::min (b.y, visible.y1);
+		
+		double d = distance_to_segment_squared (p, a, b, t, at);
+		
+		if (t < 0.0 || t > 1.0) {
+			return false;
+		}
+		
+		if (d < threshold) {
 			return true;
 		}
+		
 	}
 	
 	return false;