Rework cave shader - make default proportional for variable world height

forge-1.12.2/src/main/java/org/dynmap/forge_1_12_2/ForgeMapChunkCache.java

@@ -109,6 +109,7 @@ public class ForgeMapChunkCache extends MapChunkCache
         private BlockStep laststep;
         private DynmapBlockState blk;
         private final int worldheight;
+        private final int ymin, sealevel;
         private final int x_base;
         private final int z_base;
 
@@ -124,6 +125,8 @@ public class ForgeMapChunkCache extends MapChunkCache
 
             initialize(x0, y0, z0);
             worldheight = w.getHeight();
+            ymin = 0;
+            sealevel = w.getSeaLevel();
         }
         @Override
         public final void initialize(int x0, int y0, int z0)
@@ -719,6 +722,14 @@ public class ForgeMapChunkCache extends MapChunkCache
             return worldheight;
         }
         @Override
+        public int getWorldYMin() {
+        	return ymin;
+        }
+        @Override
+        public int getWorldSeaLevel() {
+        	return sealevel;
+        }
+        @Override
         public long getBlockKey()
         {
             return (((chunkindex * worldheight) + y) << 8) | (bx << 4) | bz;