Implement cloud alpha overlay tiles layer

This works very well for the most part with
two small problems:

- Webtiles will not support this yet (in probability,
  this will stop any clouds showing in webtiles)

- Floor items interact strangely and will draw over
  the top of clouds instead of behind them

1 files changed, 2 insertions, 0 deletions

diff --git a/crawl-ref/source/tilebuf.h b/crawl-ref/source/tilebuf.h
index 8e0402868d..911b906368 100644
--- a/crawl-ref/source/tilebuf.h
+++ b/crawl-ref/source/tilebuf.h
@@ -87,6 +87,8 @@ public:
 
     void add(tileidx_t idx, int x, int y, int z = 0, bool submerged = false,
              bool ghost = false, int ox = 0, int oy = 0, int ymax = -1);
+    void add_alpha(tileidx_t idx, int x, int y, int z,
+                   int ox, int oy, int ymax, int alpha);
 
     void draw() const;
     void clear();