display guide anchor on canvas; anchor and angle can be edited by mouse

(bzr r7180)

2 files changed, 16 insertions, 1 deletions

diff --git a/src/2geom/point.cpp b/src/2geom/point.cpp
index 5dd7b52f2..b8a858f8d 100644
--- a/src/2geom/point.cpp
+++ b/src/2geom/point.cpp
@@ -2,7 +2,7 @@
 #include <assert.h>
 #include <2geom/coord.h>
 #include <2geom/isnan.h> //temporary fix for isnan()
-#include <2geom/matrix.h>
+#include <2geom/transforms.h>
 
 namespace Geom {
 
@@ -150,6 +150,18 @@ Point &Point::operator*=(Matrix const &m)
     return *this;
 }
 
+Point constrain_angle(Point const &ref, Point const &pt, unsigned int n, Point const &dir)
+{
+    // for special cases we could perhaps use faster routines
+    if (n == 0.0) {
+        return pt;
+    }
+    Point diff(pt - ref);
+    double angle = -angle_between(diff, dir);
+    double k = round(angle * (double)n / (2.0*M_PI));
+    return ref + dir * Rotate(k * 2.0 * M_PI / (double)n) * L2(diff);
+}
+
 }  //Namespace Geom
 
 /*
diff --git a/src/2geom/point.h b/src/2geom/point.h
index d89b53f83..39538c832 100644
--- a/src/2geom/point.h
+++ b/src/2geom/point.h
@@ -229,6 +229,9 @@ Point operator*(Point const &v, Matrix const &m);
 
 Point operator/(Point const &p, Matrix const &m);
 
+/** Constrains the angle between a and b to a multiple of pi/n with respect to dir. */
+Point constrain_angle(Point const &ref, Point const &pt, unsigned int n = 4, Geom::Point const &dir = Geom::Point(1,0));
+
 } /* namespace Geom */
 
 #endif /* !SEEN_Geom_POINT_H */