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, 87 insertions, 0 deletions

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;
+}
+