inlined 'iterate_chunkblocks' (backported from Xon's code)

From the discussion in the massive Issue #271 discussion:
https://github.com/brownan/Minecraft-Overviewer/issues/#issue/271

chunk.py

@@ -97,21 +97,6 @@ def get_tileentity_data(level):
     data = level['TileEntities']
     return data
 
-def iterate_chunkblocks(xoff,yoff):
-    """Iterates over the 16x16x128 blocks of a chunk in rendering order.
-    Yields (x,y,z,imgx,imgy)
-    x,y,z is the block coordinate in the chunk
-    imgx,imgy is the image offset in the chunk image where that block should go
-    """
-    for x in xrange(15,-1,-1):
-        for y in xrange(16):
-            imgx = xoff + x*12 + y*12
-            imgy = yoff - x*6 + y*6 + 128*12 + 16*12//2
-            for z in xrange(128):
-                yield x,y,z,imgx,imgy
-                imgy -= 12
-
-
 # This set holds blocks ids that can be seen through, for occlusion calculations
 transparent_blocks = set([0, 6, 8, 9, 18, 20, 37, 38, 39, 40, 44, 50, 51, 52, 53, 55,
     59, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 74, 75, 76, 77, 78, 79, 81, 83, 85])
@@ -689,7 +674,14 @@ class ChunkRenderer(object):
         if not img:
             img = Image.new("RGBA", (384, 1728), (38,92,255,0))
 
-        for x,y,z,imgx,imgy in iterate_chunkblocks(xoff,yoff):
+        for x in xrange(15,-1,-1):
+            for y in xrange(16):
+                imgx = xoff + x*12 + y*12
+                imgy = yoff - x*6 + y*6 + 128*12 + 16*12//2
+                imgy += 12
+                for z in xrange(128):
+                    imgy -= 12
+
                     blockid = blocks[x,y,z]
 
                     # the following blocks don't have textures that can be pre-computed from the blockid