Change corner handling.

ray_def should now deal with hitting corners gracefully, though the
raycasting will still discard such rays. If a ray hits a corner
between two diamonds, it will stay there, and calling ray_def::pos
will arbitrarily give one of the squares -- this is not optimal,
but these rays shouldn't usually show up anyway.

4 files changed, 54 insertions, 7 deletions

diff --git a/crawl-ref/source/geom2d.cc b/crawl-ref/source/geom2d.cc
index 62930aec9c..eef902f14d 100644
--- a/crawl-ref/source/geom2d.cc
+++ b/crawl-ref/source/geom2d.cc
@@ -68,8 +68,9 @@ static double tdist(const ray &r, const lineseq &ls)
 }
 
 // Shoot the ray inside the next cell.
-// Returns true if succesfully advanced, false if aborted due to corner.
-bool nextcell(ray &r, const grid &g, bool pass_corner)
+// Returns true if succesfully advanced into a new cell,
+// false if it hit a corner.
+bool nextcell(ray &r, const grid &g)
 {
     // ASSERT(!parallel(g.vert, g.horiz));
     lineseq ls;
@@ -84,7 +85,12 @@ bool nextcell(ray &r, const grid &g, bool pass_corner)
         double sd = tdist(r, g.ls1);
         double td = tdist(r, g.ls2);
         if (double_is_zero(s - t))
+        {
+            // Move onto the corner. The fact that we're on a corner
+            // should be tracked externally.
+            r.advance(s);
             return (false);
+        }
         double dmin = std::min(s,t);
         double dnext = std::min(std::max(s,t), dmin + std::min(sd, td));
         r.advance((dmin + dnext) / 2.0);
@@ -96,6 +102,19 @@ bool nextcell(ray &r, const grid &g, bool pass_corner)
     return (true);
 }
 
+void movehalfcell(ray &r, const grid &g)
+{
+    // ASSERT(!parallel(g.vert, g.horiz));
+    lineseq ls;
+    double t;
+    if (parallel(r.dir, g.ls1.f))
+        t = tdist(r, g.ls2);
+    else if (parallel(r.dir, g.ls2.f))
+        t = tdist(r, g.ls1);
+    else
+        t = std::min(tdist(r, g.ls1), tdist(r, g.ls2));
+    r.advance(0.5 * t);
+}
 
 // vector space implementation
 
diff --git a/crawl-ref/source/geom2d.h b/crawl-ref/source/geom2d.h
index d65ea06842..37b62745df 100644
--- a/crawl-ref/source/geom2d.h
+++ b/crawl-ref/source/geom2d.h
@@ -76,7 +76,8 @@ struct grid
 
 double intersect(const ray &r, const line &l);
 double nextintersect(const ray &r, const lineseq &ls);
-bool nextcell(ray &r, const grid &g, bool pass_corner);
+bool nextcell(ray &r, const grid &g);
+void movehalfcell(ray &r, const grid &g);
 
 }
 
diff --git a/crawl-ref/source/ray.cc b/crawl-ref/source/ray.cc
index e6952f2102..bbf812009f 100644
--- a/crawl-ref/source/ray.cc
+++ b/crawl-ref/source/ray.cc
@@ -20,16 +20,42 @@ static int ifloor(double d)
 
 coord_def ray_def::pos() const
 {
-    // TODO: Assert we're in a central diamond.
+    // XXX: pretty arbitrary if we're just on a corner.
     int x = ifloor(r.start.x);
     int y = ifloor(r.start.y);
     return (coord_def(x, y));
 }
 
+// Return false if we passed or hit a corner.
 bool ray_def::advance()
 {
-    return (geom::nextcell(r, diamonds, true)
-            && geom::nextcell(r, diamonds, false));
+    if (on_corner)
+    {
+        on_corner = false;
+        geom::movehalfcell(r, diamonds);
+    }
+    else
+    {
+        // Starting inside a diamond.
+        bool c = !geom::nextcell(r, diamonds);
+
+        if (c)
+        {
+            // r is now on a corner, going from diamond to diamond.
+            geom::movehalfcell(r, diamonds);
+            return (false);
+        }
+    }
+    // Now inside a non-diamond.
+
+    if (geom::nextcell(r, diamonds))
+        return (true);
+    else
+    {
+        // r is now on a corner, going from non-diamond to non-diamond.
+        on_corner = true;
+        return (false);
+    }
 }
 
 void ray_def::advance_and_bounce()
diff --git a/crawl-ref/source/ray.h b/crawl-ref/source/ray.h
index 477f8fcbf7..671ca0fa8a 100644
--- a/crawl-ref/source/ray.h
+++ b/crawl-ref/source/ray.h
@@ -11,11 +11,12 @@
 struct ray_def
 {
     geom::ray r;
+    bool on_corner;
     int cycle_idx;
 
     ray_def() {}
     ray_def(const geom::ray& _r)
-        : r(_r), cycle_idx(0) {}
+        : r(_r), on_corner(false), cycle_idx(0) {}
 
     coord_def pos() const;
     bool advance();