Index: trunk/src/layer_grp.c
===================================================================
--- trunk/src/layer_grp.c	(revision 8680)
+++ trunk/src/layer_grp.c	(revision 8681)
@@ -340,6 +340,38 @@
 		memmove(&stk->grp[from + delta], &stk->grp[from], sizeof(pcb_layer_group_t) * remaining);
 }
 
+int pcb_layergrp_step_layer(pcb_layer_group_t *grp, pcb_layer_id_t lid, int delta)
+{
+	int idx, idx2;
+	pcb_layer_id_t tmp;
+
+	for(idx = 0; idx < grp->len; idx++) {
+		if (grp->lid[idx] == lid) {
+			if (delta > 0) {
+				if (idx == grp->len - 1) /* already the last */
+					return 0;
+				idx2 = idx+1;
+				goto swap;
+			}
+			else if (delta < 0) {
+				if (idx == 0) /* already the last */
+					return 0;
+				idx2 = idx-1;
+				goto swap;
+			}
+			else
+				return -1;
+		}
+	}
+	return -1;
+
+	swap:;
+	tmp = grp->lid[idx];
+	grp->lid[idx] =grp->lid[idx2];
+	grp->lid[idx2] = tmp;
+	return 0;
+}
+
 int pcb_layergrp_del(pcb_board_t *pcb, pcb_layergrp_id_t gid, int del_layers)
 {
 	int n;
Index: trunk/src/layer_grp.h
===================================================================
--- trunk/src/layer_grp.h	(revision 8680)
+++ trunk/src/layer_grp.h	(revision 8681)
@@ -107,6 +107,10 @@
 /* Insert a new layer group in the layer stack after the specified group */
 pcb_layer_group_t *pcb_layergrp_insert_after(pcb_board_t *pcb, pcb_layergrp_id_t where);
 
+/* Move lid 1 step towards the front (delta=-1) or end (delta=+1) of the
+   layer list of the group. Return 0 on success (even when already reached
+   the end of the list) or -1 on error */
+int pcb_layergrp_step_layer(pcb_layer_group_t *grp, pcb_layer_id_t lid, int delta);
 
 /* Enable/disable inhibition of layer changed events during layer group updates */
 void pcb_layergrp_inhibit_inc(void);