forwardport #6477 (#6487)

* icy stone walls variation for Xos, based on adjacent terrain, not new code

* more variations for rocks, rubble, and snowbits

data/core/terrain-graphics.cfg

@@ -845,6 +845,7 @@ C*,K*,X*,Q*,W*,Ai,M*,*^V*,*^B*,_off^_usr#enddef
 {NEW:WALL_CORNER                 Xot           (!,Xo*,Xu*)      walls/stone/catacombs/wall-stone ALTERNATIVE=Xo*}
 {NEW:WALL_CORNER                 Xof^Efm       (!,Xo*,Xu*)      walls/stone/overgrown/wall-flowers ALTERNATIVE=Xof}
 {NEW:WALL_CORNER                 Xof           (!,Xo*,Xu*)      walls/stone/overgrown/wall-stone}
+{NEW:WALL_CORNER                 Xos           (Aa,Ai,Ha)       walls/stone/wall-stone-snow}
 {NEW:WALL_CORNER                 Xo*           (!,Xo*,Xu*)      walls/stone/wall-stone}
 {NEW:WALL_A10                    Xol           (!,Xu*,Xo*)      walls/stone/lit/wall-stone-lit}
 {NEW:WALL                        Xoi           (!,Xu*,Xo*)      walls/stone/wall-stone-white}
@@ -860,6 +861,7 @@ C*,K*,X*,Q*,W*,Ai,M*,*^V*,*^B*,_off^_usr#enddef
 {NEW:WALL_MINOR_VARIANTS         Xot           Xo*              (!,Xu*,Xo*)      walls/stone/catacombs/wall-stone}
 {NEW:WALL                        Xof^Efm       (!,Xu*,Xo*)      walls/stone/overgrown/wall-stone OVERLAYIMAGE=terrain/walls/stone/overgrown/wall-flowers}
 {NEW:WALL                        Xof           (!,Xu*,Xo*)      walls/stone/overgrown/wall-stone}
+{NEW:WALL                        Xos           (Aa,Ai,Ha)      walls/stone/wall-stone-snow ADJACENT2=!,Xu*,Xo*}
 {NEW:WALL                        Xo*           (!,Xu*,Xo*)      walls/stone/wall-stone}
 
 # New Generic Castle-to Chasm transition

data/core/terrain-graphics/new-macros.cfg

@@ -2775,6 +2775,9 @@ _off^Fp#endarg
 #arg PROB
 100#endarg
 
+#arg ADJACENT2
+{ADJACENT}#endarg
+
 #arg LAYER
 0#endarg
 
@@ -2801,7 +2804,7 @@ terrain/walls/dummy/dummy#endarg
         [/tile]
         [tile]
             pos=2
-            type={ADJACENT}
+            type={ADJACENT2}
             set_no_flag={FLAG}-@R2
         [/tile]
         [tile]
@@ -2826,6 +2829,39 @@ terrain/walls/dummy/dummy#endarg
         map="
 2
 ,  3
+1"
+        [tile]
+            pos=1
+            type={TERRAINLIST}
+            set_no_flag={FLAG}-@R0
+        [/tile]
+        [tile]
+            pos=2
+            type={ADJACENT}
+            set_no_flag={FLAG}-@R2
+        [/tile]
+        [tile]
+            pos=3
+            type={ADJACENT2}
+            set_no_flag={FLAG}-@R4
+        [/tile]
+
+        rotations=tr,r,br,bl,l,tl
+        probability={PROB}
+
+        [image]
+            layer={LAYER}
+            base={BASE}
+            # no @V in the BLIT() because there may not be a matching overlay image for each base variation
+            name={IMAGESTEM}@V-convex-@R0.png~BLIT({OVERLAYIMAGE}-convex-@R0.png)
+            variations=";2;3;4;5;6"
+        [/image]
+    [/terrain_graphics]
+
+    [terrain_graphics]
+        map="
+2
+,  3
 1"
         [tile]
             pos=1