one standing clump per grass tile; ledge pillars at ledge height

Grass: each 8x8 tile is one whole clump, so it stands as ONE full-height
slab at its own depth. The first cut split every tile again into its top
and bottom four art rows and stood those at two different depths, which
cut each blade in half -- two 4px stubs 4px apart rather than a tuft.
A cell's 2x2 tiles still stand independently, so the player walks
between the north and south rows.

Ledges: $34 is the cliff slope's foot AND the pillar between hop-down
segments. Pinned `wall` with the rest of the slope chain it stood 16px
beside a 6px lip, breaking the ledge line with blocks nearly three times
its height. At ledge height the run reads continuous, and the Diglett
mound is unchanged -- its foot row reads as the talus it is drawn as.

lib/Structures.lua

@@ -2091,14 +2091,21 @@ end
 
 -- ---- tall grass ----
 
--- A tall-grass tile draws its four tuft segments in two ROWS: the art's
--- top half is one row of grass, the bottom half another. Each row stands
--- as a thin per-pixel slab at its own drawn depth inside the tile, over
--- the flat grass base the tile already renders -- so the player walks
--- BETWEEN rows, and the southern row occludes their feet the way the 2D
--- grass overdraw did. Transparency respected: only the tuft strokes stand.
--- Runs of adjacent pixels merge into single quads, and one template per
--- grass tile id is stamped across the map (grass comes in fields).
+-- A tall-grass CELL is four tufts: 2x2 tiles, and each 8x8 tile is one
+-- whole clump of grass. Each tile stands as its own thin per-pixel slab
+-- at ITS OWN depth -- the cell's north tile row in the north half of the
+-- cell, the south row in the south half -- over the flat grass base the
+-- tile already renders. So the player walks BETWEEN the two rows, and
+-- the southern row occludes their feet the way the 2D grass overdraw
+-- did. Transparency respected: only the tuft strokes stand. Runs of
+-- adjacent pixels merge into single quads, and one template per grass
+-- tile id is stamped across the map (grass comes in fields).
+--
+-- One tile is ONE standing piece, full height. The first cut split each
+-- tile again into its top and bottom four art rows and stood those at
+-- two different depths, which cut every blade that runs down the tile
+-- clean in half -- the two halves ended up 4px tall and 4px apart in
+-- depth, so a clump read as two stubs rather than one tuft.
 local GRASS_THICK = 2
 
 local function grassTemplate(map, data, tileId)
@@ -2115,49 +2122,48 @@ local function grassTemplate(map, data, tileId)
   end
 
   local quads = {}
-  for half = 0, 1 do
-    local rowBase = half * 4
-    local zMid = half == 0 and 2.5 or 6.5
-    local zB, zF = zMid - GRASS_THICK / 2, zMid + GRASS_THICK / 2
-    for iy = 0, 3 do
-      local yTop = 4 - iy
-      local yBot = yTop - 1
-      local ix = 0
-      while ix < 8 do
-        if opaque(ix, rowBase + iy) then
-          local ix2 = ix
-          while ix2 + 1 < 8 and opaque(ix2 + 1, rowBase + iy) do
-            ix2 = ix2 + 1
-          end
-          local u0 = (ax0 + ix + 0.05) / atlasW
-          local u1 = (ax0 + ix2 + 0.95) / atlasW
-          local v0 = (ay0 + rowBase + iy + 0.05) / atlasH
-          local v1 = (ay0 + rowBase + iy + 0.95) / atlasH
-          quads[#quads + 1] = {           -- front
-            { ix, yBot, zF }, { ix2 + 1, yBot, zF },
+  -- the slab stands across the middle of its own tile, so the two tile
+  -- rows of a cell are half a cell apart in depth
+  local zMid = 4
+  local zB, zF = zMid - GRASS_THICK / 2, zMid + GRASS_THICK / 2
+  for iy = 0, 7 do
+    local yTop = 8 - iy
+    local yBot = yTop - 1
+    local ix = 0
+    while ix < 8 do
+      if opaque(ix, iy) then
+        local ix2 = ix
+        while ix2 + 1 < 8 and opaque(ix2 + 1, iy) do
+          ix2 = ix2 + 1
+        end
+        local u0 = (ax0 + ix + 0.05) / atlasW
+        local u1 = (ax0 + ix2 + 0.95) / atlasW
+        local v0 = (ay0 + iy + 0.05) / atlasH
+        local v1 = (ay0 + iy + 0.95) / atlasH
+        quads[#quads + 1] = {           -- front
+          { ix, yBot, zF }, { ix2 + 1, yBot, zF },
+          { ix2 + 1, yTop, zF }, { ix, yTop, zF },
+          uv = { { u0, v1 }, { u1, v1 }, { u1, v0 }, { u0, v0 } },
+          shade = 1,
+        }
+        quads[#quads + 1] = {           -- back
+          { ix2 + 1, yBot, zB }, { ix, yBot, zB },
+          { ix, yTop, zB }, { ix2 + 1, yTop, zB },
+          uv = { { u1, v1 }, { u0, v1 }, { u0, v0 }, { u1, v0 } },
+          shade = 0.68,
+        }
+        -- blade tips: a top strip where the row above is clear
+        if not opaque(ix, iy - 1) then
+          quads[#quads + 1] = {
+            { ix, yTop, zB }, { ix2 + 1, yTop, zB },
             { ix2 + 1, yTop, zF }, { ix, yTop, zF },
-            uv = { { u0, v1 }, { u1, v1 }, { u1, v0 }, { u0, v0 } },
+            uv = { { u0, v0 }, { u1, v0 }, { u1, v0 }, { u0, v0 } },
             shade = 1,
           }
-          quads[#quads + 1] = {           -- back
-            { ix2 + 1, yBot, zB }, { ix, yBot, zB },
-            { ix, yTop, zB }, { ix2 + 1, yTop, zB },
-            uv = { { u1, v1 }, { u0, v1 }, { u0, v0 }, { u1, v0 } },
-            shade = 0.68,
-          }
-          -- blade tips: a top strip where the row above is clear
-          if not opaque(ix, rowBase + iy - 1) then
-            quads[#quads + 1] = {
-              { ix, yTop, zB }, { ix2 + 1, yTop, zB },
-              { ix2 + 1, yTop, zF }, { ix, yTop, zF },
-              uv = { { u0, v0 }, { u1, v0 }, { u1, v0 }, { u0, v0 } },
-              shade = 1,
-            }
-          end
-          ix = ix2 + 1
-        else
-          ix = ix + 1
         end
+        ix = ix2 + 1
+      else
+        ix = ix + 1
       end
     end
   end