Index: layer.h
===================================================================
--- layer.h	(revision 19367)
+++ layer.h	(revision 19368)
@@ -160,7 +160,7 @@
 };
 
 /* returns the layer number for the passed copper or silk layer pointer */
-pcb_layer_id_t pcb_layer_id(pcb_data_t *Data, pcb_layer_t *Layer);
+pcb_layer_id_t pcb_layer_id(const pcb_data_t *Data, const pcb_layer_t *Layer);
 
 
 /* the offsets of the two additional special layers (e.g. silk) for 'component'
@@ -233,13 +233,13 @@
 
 
 /* returns a bitfield of pcb_layer_type_t; returns 0 if layer_idx or layer is invalid. */
-unsigned int pcb_layer_flags(pcb_board_t *pcb, pcb_layer_id_t layer_idx);
-unsigned int pcb_layer_flags_(pcb_layer_t *layer);
+unsigned int pcb_layer_flags(const pcb_board_t *pcb, pcb_layer_id_t layer_idx);
+unsigned int pcb_layer_flags_(const pcb_layer_t *layer);
 
 /* Return the purpi of the group of a layer; if out is not NULL, also copy
    a pointer to the purpose string there (valid until a layer change) */
-int pcb_layer_purpose(pcb_board_t *pcb, pcb_layer_id_t layer_idx, const char **out);
-int pcb_layer_purpose_(pcb_layer_t *layer, const char **out);
+int pcb_layer_purpose(const pcb_board_t *pcb, pcb_layer_id_t layer_idx, const char **out);
+int pcb_layer_purpose_(const pcb_layer_t *layer, const char **out);
 
 
 /* map bits of a layer type (call cb for each bit set); return number of bits
@@ -266,9 +266,9 @@
    The version that ends in 'p' also matches purpose if purpi is not -1
    and/or purpose is not NULL.
 */
-int pcb_layer_list(pcb_board_t *pcb, pcb_layer_type_t mask, pcb_layer_id_t *res, int res_len);
-int pcb_layer_list_any(pcb_board_t *pcb, pcb_layer_type_t mask, pcb_layer_id_t *res, int res_len);
-int pcb_layer_listp(pcb_board_t *pcb, pcb_layer_type_t mask, pcb_layer_id_t *res, int res_len, int purpi, const char *purpose);
+int pcb_layer_list(const pcb_board_t *pcb, pcb_layer_type_t mask, pcb_layer_id_t *res, int res_len);
+int pcb_layer_list_any(const pcb_board_t *pcb, pcb_layer_type_t mask, pcb_layer_id_t *res, int res_len);
+int pcb_layer_listp(const pcb_board_t *pcb, pcb_layer_type_t mask, pcb_layer_id_t *res, int res_len, int purpi, const char *purpose);
 
 
 /**** layer creation (for load/import code) ****/
@@ -335,7 +335,7 @@
 
 /* Return the real layer, resolving layer bindings. Returns NULL on
    error (e.g. binding loop) */
-PCB_INLINE pcb_layer_t *pcb_layer_get_real(pcb_layer_t *layer)
+PCB_INLINE pcb_layer_t *pcb_layer_get_real(const pcb_layer_t *layer)
 {
 	int rec = 0;
 
@@ -345,7 +345,7 @@
 		if ((rec > PCB_MAX_BOUND_LAYER_RECURSION) || (layer == NULL))
 			return NULL;
 	}
-	return layer;
+	return (pcb_layer_t *)layer;
 }
 
 /* list of virtual layers: these are generated by the draw code but do not