Index: trunk/src/hid_cam.c
===================================================================
--- trunk/src/hid_cam.c	(revision 37319)
+++ trunk/src/hid_cam.c	(revision 37320)
@@ -263,6 +263,8 @@
 				dst->flip_x = 1;
 			else if (strcmp(curr, "flip_y") == 0)
 				dst->flip_y = 1;
+			else if (strcmp(curr, "force_nonempty") == 0)
+				dst->force_nonempty = 1;
 			else
 				rnd_message(RND_MSG_ERROR, "CAM: ignoring unknown global parameter [%s]\n", curr);
 		}
@@ -361,6 +363,13 @@
 	return -1;
 }
 
+rnd_bool pcb_cam_layergrp_is_empty(pcb_cam_t *dst, pcb_board_t *PCB, rnd_layergrp_id_t group)
+{
+	if (dst->force_nonempty)
+		return 0;
+	return pcb_layergrp_is_empty(PCB, group);
+}
+
 int pcb_cam_end(pcb_cam_t *dst)
 {
 	free(dst->inst);
Index: trunk/src/hid_cam.h
===================================================================
--- trunk/src/hid_cam.h	(revision 37319)
+++ trunk/src/hid_cam.h	(revision 37320)
@@ -23,6 +23,7 @@
 	unsigned int okempty_group:1;   /* do not warn if no group exported */
 	unsigned flip_x:1;
 	unsigned flip_y:1;
+	unsigned force_nonempty:1;      /* export even if layer group is empty */
 
 	/* private/internal/cache */
 	const char *fn_template;
@@ -97,4 +98,8 @@
    directly, instead  of manipulating an attribute */
 char *pcb_derive_default_filename_(const char *pcbfile, const char *suffix);
 
+/* Returns whether the layer groups hould be considered empty; most of the times
+   this matches pcb_layergrp_is_empty(), but cam may override this */
+rnd_bool pcb_cam_layergrp_is_empty(pcb_cam_t *dst, pcb_board_t *PCB, rnd_layergrp_id_t group);
+
 #endif