Index: trunk/src/layer.c
===================================================================
--- trunk/src/layer.c	(revision 19367)
+++ trunk/src/layer.c	(revision 19368)
@@ -226,7 +226,7 @@
 	return pcb_false;
 }
 
-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)
 {
 	if (Layer->parent_type == PCB_PARENT_UI)
 		return pcb_uilayer_get_id(Layer);
@@ -244,7 +244,7 @@
 	return -1;
 }
 
-unsigned int pcb_layer_flags(pcb_board_t *pcb, pcb_layer_id_t layer_idx)
+unsigned int pcb_layer_flags(const pcb_board_t *pcb, pcb_layer_id_t layer_idx)
 {
 	pcb_layer_t *l;
 
@@ -261,7 +261,7 @@
 	return pcb_layergrp_flags(pcb, l->meta.real.grp);
 }
 
-unsigned int pcb_layer_flags_(pcb_layer_t *layer)
+unsigned int pcb_layer_flags_(const pcb_layer_t *layer)
 {
 
 	/* real layer: have to do a layer stack based lookup; but at least we have a real layer ID  */
@@ -292,7 +292,7 @@
 	return layer->meta.bound.type;
 }
 
-int pcb_layer_purpose(pcb_board_t *pcb, pcb_layer_id_t layer_idx, const char **out)
+int pcb_layer_purpose(const pcb_board_t *pcb, pcb_layer_id_t layer_idx, const char **out)
 {
 	pcb_layergrp_t *grp;
 
@@ -311,7 +311,7 @@
 		return -1;
 	}
 
-	grp = pcb_get_layergrp(pcb, pcb->Data->Layer[layer_idx].meta.real.grp);
+	grp = pcb_get_layergrp((pcb_board_t *)pcb, pcb->Data->Layer[layer_idx].meta.real.grp);
 
 	if (out != NULL) {
 		if (grp == NULL) {
@@ -328,7 +328,7 @@
 	return grp->purpi;
 }
 
-int pcb_layer_purpose_(pcb_layer_t *layer, const char **out)
+int pcb_layer_purpose_(const pcb_layer_t *layer, const char **out)
 {
 	/* real layer: have to do a layer stack based lookup; but at least we have a real layer ID  */
 	if (!layer->is_bound) {
@@ -389,7 +389,7 @@
 
 
 
-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(const pcb_board_t *pcb, pcb_layer_type_t mask, pcb_layer_id_t *res, int res_len)
 {
 	int n, used = 0;
 	pcb_virt_layer_t *v;
@@ -411,7 +411,7 @@
 }
 
 /* optimization: code dup for speed */
-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_listp(const pcb_board_t *pcb, pcb_layer_type_t mask, pcb_layer_id_t *res, int res_len, int purpi, const char *purpose)
 {
 	int n, used = 0;
 	pcb_virt_layer_t *v;
@@ -439,7 +439,7 @@
 }
 
 
-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_list_any(const pcb_board_t *pcb, pcb_layer_type_t mask, pcb_layer_id_t *res, int res_len)
 {
 	int n, used = 0;
 	pcb_virt_layer_t *v;
Index: trunk/src/layer.h
===================================================================
--- trunk/src/layer.h	(revision 19367)
+++ trunk/src/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