Add new ContentParamType2 "CPT2_DEGROTATE"

This might break some mods, but it is important for all uses of the param2 to
be documented.

This doesn't need a serialisation version or network protocol version change,
as old clients will still work on new servers, and it is bearable to have
new clients getting non rotated plants on old servers.

doc/lua_api.txt

@@ -538,6 +538,10 @@ node definition:
       0 = y+    1 = z+    2 = z-    3 = x+    4 = x-    5 = y-
       facedir's two less significant bits are rotation around the axis
     paramtype2 == "leveled"
+    paramtype2 == "degrotate"
+    ^ The rotation of this node is stored in param2. Plants are rotated this way.
+      Values range 0 - 179. The value stored in param2 is multiplied by two to
+      get the actual rotation of the node.
     collision_box = {
       type = "fixed",
       fixed = {

src/content_mapblock.cpp

@@ -1125,16 +1125,16 @@ void mapblock_mesh_generate_special(MeshMakeData *data,
 					video::S3DVertex( s,-BS/2 + s*2,0, 0,0,0, c, 1,0),
 					video::S3DVertex(-s,-BS/2 + s*2,0, 0,0,0, c, 0,0),
 				};
+				float rotate_degree = 0;
+				if (f.param_type_2 == CPT2_DEGROTATE)
+					rotate_degree = n.param2 * 2;
 
-				if(j == 0)
-				{
+				if (j == 0) {
 					for(u16 i = 0; i < 4; i++)
-						vertices[i].Pos.rotateXZBy(46 + n.param2 * 2);
-				}
-				else if(j == 1)
-				{
+						vertices[i].Pos.rotateXZBy(46 + rotate_degree);
+				} else if (j == 1) {
 					for(u16 i = 0; i < 4; i++)
-						vertices[i].Pos.rotateXZBy(-44 + n.param2 * 2);
+						vertices[i].Pos.rotateXZBy(-44 + rotate_degree);
 				}
 
 				for (int i = 0; i < 4; i++)

src/nodedef.h

@@ -63,6 +63,8 @@ enum ContentParamType2
 	CPT2_WALLMOUNTED,
 	// Block level like FLOWINGLIQUID
 	CPT2_LEVELED,
+	// 2D rotation for things like plants
+	CPT2_DEGROTATE,
 };
 
 enum LiquidType

src/script/cpp_api/s_node.cpp

@@ -57,6 +57,7 @@ struct EnumString ScriptApiNode::es_ContentParamType2[] =
 		{CPT2_FACEDIR, "facedir"},
 		{CPT2_WALLMOUNTED, "wallmounted"},
 		{CPT2_LEVELED, "leveled"},
+		{CPT2_DEGROTATE, "degrotate"},
 		{0, NULL},
 	};