Implement monster_iterator.

monster_iterator allows iterating over live monsters in
env.mgrid, possibly subject to some location/visibility
restrictions.

Possible restrictions:
- within some radius (circle_def::contains(mon->pos())
- position inside some LOS (los_def::see_cell(mon->pos())
- visible to some actor (actor::can_see(mon))

Sample use:

for (int i = 0; i < MAX_MONSTERS; ++i)
{
    monsters* const monster = &menv[i];
    if (!monster->alive())
        continue;
    // ...

// becomes

for (monster_iterator mi; mi; ++mi)
{
    // ..., replacing monster-> by mi->
    //      and monster by *mi

If you were checking for mons_near(monster), use
    monster_iterator mi(&you.get_los());
if you were checking for you.can_see(monster), use
    monster_iterator mi(&you);
if you were checking for
(monster->pos()-you.pos()).abs() <= r*r+1, use
    monster_iterator mi(circle_def(you.pos(), r, C_ROUND)).

This is not as general as one might hope, but it should
allow reducing the amount of code that knows how monsters
are stored.

1 files changed, 49 insertions, 0 deletions

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