include and translate texture slots during copy&paste

When blocks of map geometry are copy-pasted between maps (or xmaps), this
commit translates the texture slot numbers between different texture
config sets. Missing textures are assigned a slot in the target map.

When texture slots are added, automapconfig gets enabled.

If the paste gets removed by the undo function, the newly assigned texture
slots will NOT be removed. This is by design.

source/src/texture.cpp

@@ -1036,3 +1036,51 @@ void edittextureslot(int *n, char *scale, char *name) // edit slot parameters !=
 }
 COMMAND(edittextureslot, "iss");
 
+// helper functions to allow copy&paste between different maps while keeping the proper textures assigned
+// (pasting will add any missing texture slots)
+
+void *texconfig_copy()
+{
+    vector<Slot> *s = new vector<Slot>;
+    loopv(slots) s->add(slots[i]);
+    return (void *)s;
+}
+
+void texconfig_delete(void *s)
+{
+    delete (vector<Slot> *)s;
+}
+
+uchar *texconfig_paste(void *_s, uchar *usedslots) // create mapping table to translate pasted geometry to this maps texture list - add any missing textures
+{
+    vector<Slot> *s = (vector<Slot> *)_s;
+    static uchar res[256];
+    loopi(256) res[i] = i;
+    loopi(256) if(usedslots[i] && s->inrange(i))
+    {
+        Slot &os = (*s)[i];
+        bool found = false;
+        loopvj(slots)
+        {
+            if(slots[j].scale == os.scale && !strcmp(slots[j].name, os.name))
+            {
+                res[i] = j;
+                found = true;
+                break;
+            }
+        }
+        if(!found)
+        {
+            if(slots.length() < 255)
+            {
+                res[i] = slots.length();
+                _texture(slots.add(), &os.scale, os.name);
+                conoutf("added texture \"%s\" (scale %.7g) in slot #%d", os.name, os.scale, res[i]);
+                if(!(hdr.flags & MHF_AUTOMAPCONFIG)) automapconfig(); // make sure, the new texture slots will be saved with the map
+            }
+            else conoutf("\f3failed to add texture \"%s\" (scale %.7g): no texture slot available", os.name, os.scale);
+        }
+    }
+    return res;
+}
+