4 files changed, 55 insertions, 3 deletions
diff --git a/crawl-ref/source/geom2d.cc b/crawl-ref/source/geom2d.cc
index de8d86724b..35ec5138ae 100644
--- a/crawl-ref/source/geom2d.cc
+++ b/crawl-ref/source/geom2d.cc
@@ -44,6 +44,11 @@ double intersect(const ray &r, const line &l)
     return (t);
 }
 
+double lineseq::index(const vector &v) const
+{
+    return ((f(v) - offset) / dist);
+}
+
 // Find the next intersection of r with a line in ls.
 double nextintersect(const ray &r, const lineseq &ls)
 {
@@ -129,6 +134,9 @@ vector reflect(const vector &v, const form &f)
     return (v - 2 * f(v)/f(n) * n);
 }
 
+
+
+//////////////////////////////////////////////////
 // vector space implementation
 
 const vector& vector::operator+=(const vector &v)
diff --git a/crawl-ref/source/geom2d.h b/crawl-ref/source/geom2d.h
index 504f1ed77a..6f7e147ab1 100644
--- a/crawl-ref/source/geom2d.h
+++ b/crawl-ref/source/geom2d.h
@@ -70,6 +70,8 @@ struct lineseq
     lineseq() {}
     lineseq(double a, double b, double o, double d)
         : f(a,b), offset(o), dist(d) {}
+
+    double index(const vector &v) const;
 };
 
 struct grid
diff --git a/crawl-ref/source/ray.cc b/crawl-ref/source/ray.cc
index dff1d3e82a..56fc3058d1 100644
--- a/crawl-ref/source/ray.cc
+++ b/crawl-ref/source/ray.cc
@@ -15,6 +15,7 @@
 
 #include <cmath>
 
+#include "los.h"
 #include "ray.h"
 #include "geom2d.h"
 
@@ -26,6 +27,36 @@ static int ifloor(double d)
     return static_cast<int>(floor(d));
 }
 
+static bool double_is_integral(double d)
+{
+    return (double_is_zero(d - round(d)));
+}
+
+
+// Is v in a diamond?
+static bool in_diamond(const geom::vector &v)
+{
+    int i1 = ifloor(diamonds.ls1.index(v));
+    int i2 = ifloor(diamonds.ls2.index(v));
+    return ((i1 + i2) % 2 == 0);
+}
+
+// Is v in the interiour of a diamond?
+static bool in_diamond_int(const geom::vector &v)
+{
+    double d1 = diamonds.ls1.index(v);
+    double d2 = diamonds.ls2.index(v);
+    return (!double_is_integral(d1) && !double_is_integral(d2));
+}
+
+// Is v an intersection of grid lines?
+static bool is_corner(const geom::vector &v)
+{
+    double d1 = diamonds.ls1.index(v);
+    double d2 = diamonds.ls2.index(v);
+    return (double_is_integral(d1) && double_is_integral(d2));
+}
+
 coord_def ray_def::pos() const
 {
     // XXX: pretty arbitrary if we're just on a corner.
@@ -37,8 +68,10 @@ coord_def ray_def::pos() const
 // Return false if we passed or hit a corner.
 bool ray_def::advance()
 {
+    ASSERT(on_corner || in_diamond_int(r.start));
     if (on_corner)
     {
+        ASSERT (is_corner(r.start));
         on_corner = false;
         r.move_half_cell(diamonds);
     }
@@ -54,13 +87,19 @@ bool ray_def::advance()
             return (false);
         }
     }
+
     // Now inside a non-diamond.
+    ASSERT(!in_diamond(r.start));
 
     if (r.to_next_cell(diamonds))
+    {
+        ASSERT(in_diamond_int(r.start));
         return (true);
+    }
     else
     {
         // r is now on a corner, going from non-diamond to non-diamond.
+        ASSERT(is_corner(r.start));
         on_corner = true;
         return (false);
     }
@@ -68,7 +107,10 @@ bool ray_def::advance()
 
 void ray_def::bounce(const reflect_grid &rg)
 {
-    // XXX
+    ASSERT(in_diamond(r.start));
+    // Find out which side of the diamond r leaves through.
+    geom::ray copy = r;
+
     r.dir = -r.dir;
 }
 
diff --git a/crawl-ref/source/ray.h b/crawl-ref/source/ray.h
index cc7688571d..6748090348 100644
--- a/crawl-ref/source/ray.h
+++ b/crawl-ref/source/ray.h
@@ -17,9 +17,9 @@ struct ray_def
     bool on_corner;
     int cycle_idx;
 
-    ray_def() {}
+    ray_def() : on_corner(false), cycle_idx(-1) {}
     ray_def(const geom::ray& _r)
-        : r(_r), on_corner(false), cycle_idx(0) {}
+        : r(_r), on_corner(false), cycle_idx(-1) {}
 
     coord_def pos() const;
     bool advance();