3 files changed, 137 insertions, 0 deletions
diff --git a/crawl-ref/source/makefile.obj b/crawl-ref/source/makefile.obj
index c85450cd5f..ccbfb75aeb 100644
--- a/crawl-ref/source/makefile.obj
+++ b/crawl-ref/source/makefile.obj
@@ -103,6 +103,7 @@ mon-behv.o \
 mon-cast.o \
 mon-gear.o \
 mon-info.o \
+mon-iter.o \
 mon-pick.o \
 mon-util.o \
 monplace.o \
diff --git a/crawl-ref/source/mon-iter.cc b/crawl-ref/source/mon-iter.cc
new file mode 100644
index 0000000000..1158a9028d
--- /dev/null
+++ b/crawl-ref/source/mon-iter.cc
@@ -0,0 +1,87 @@
+#include "AppHdr.h"
+
+#include "mon-iter.h"
+
+#include "actor.h"
+#include "coord-circle.h"
+#include "env.h"
+#include "monster.h"
+
+monster_iterator::monster_iterator()
+    : restr(R_NONE), curr_mid(0)
+{
+    advance(true);
+}
+
+monster_iterator::monster_iterator(const circle_def* circle_)
+    : restr(R_CIRC), curr_mid(0), circle(circle_)
+{
+    advance(true);
+}
+
+monster_iterator::monster_iterator(const los_def* los_)
+    : restr(R_LOS), curr_mid(0), los(los_)
+{
+    advance(true);
+}
+
+monster_iterator::monster_iterator(const actor* act_)
+    : restr(R_ACT), curr_mid(0), act(act_)
+{
+    advance(true);
+}
+
+monster_iterator::operator bool() const
+{
+    return (curr_mid < MAX_MONSTERS);
+}
+
+monsters* monster_iterator::operator*() const
+{
+    return (&env.mons[curr_mid]);
+}
+
+monsters* monster_iterator::operator->() const
+{
+    return (&env.mons[curr_mid]);
+}
+
+monster_iterator& monster_iterator::operator++()
+{
+    advance();
+    return (*this);
+}
+
+monster_iterator monster_iterator::operator++(int)
+{
+    monster_iterator copy = *this;
+    ++(*this);
+    return (copy);
+}
+
+bool monster_iterator::valid(int mid) const
+{
+    monsters* mon = &env.mons[mid];
+    if (!mon->alive())
+        return (false);
+    switch (restr)
+    {
+    case R_CIRC:
+        return (circle->contains(mon->pos()));
+    case R_LOS:
+        return (los->see_cell(mon->pos()));
+    case R_ACT:
+        return (act->can_see(mon));
+    default:
+        return (true);
+    }
+}
+
+void monster_iterator::advance(bool may_stay)
+{
+    if (!may_stay)
+        ++curr_mid;
+    while (curr_mid < MAX_MONSTERS && !valid(curr_mid))
+        ++curr_mid;
+}
+
diff --git a/crawl-ref/source/mon-iter.h b/crawl-ref/source/mon-iter.h
new file mode 100644
index 0000000000..7f31831c64
--- /dev/null
+++ b/crawl-ref/source/mon-iter.h
@@ -0,0 +1,49 @@
+/*
+ * Provide a way to iterator over all monsters,
+ * subject to a few common restrictions.
+ *
+ * TODO:
+ *  - Iterate over actors?
+ */
+
+#ifndef MON_ITER_H
+#define MON_ITER_H
+
+enum restr_type
+{
+    R_NONE,
+    R_CIRC,
+    R_LOS,
+    R_ACT
+};
+
+class circle_def;
+class los_def;
+class actor;
+
+class monster_iterator
+{
+public:
+    monster_iterator();
+    monster_iterator(const circle_def* circle_);
+    monster_iterator(const los_def* los_);
+    monster_iterator(const actor* act_);
+
+    operator bool() const;
+    monsters* operator*() const;
+    monsters* operator->() const;
+    monster_iterator& operator++();
+    monster_iterator operator++(int);
+
+protected:
+    restr_type restr;
+    int curr_mid;
+    const circle_def* circle;
+    const los_def* los;
+    const actor* act;
+
+    bool valid(int mid) const;
+    void advance(bool may_stay=false);
+};
+
+#endif