allow for image offset via DURIN_IMAGE_NUMBER_OFFSET environment

variable

src/file.c

@@ -257,11 +257,12 @@ done:
 
 int get_nxs_frame(
 		const struct ds_desc_t *desc,
-		const int n,
+		const int nin,
 		void *buffer) {
 	/* detector data are the two inner most indices */
 	/* TODO: handle ndims > 3 and select appropriately */
 	int retval = 0;
+	int n = nin - desc->image_number_offset;
 	hsize_t frame_idx[3] = {n, 0, 0};
 	hsize_t frame_size[3] = {1, desc->dims[1], desc->dims[2]};
 	if (n < 0 || n >= desc->dims[0]) {
@@ -280,10 +281,11 @@ done:
 
 int get_dectris_eiger_frame(
 		const struct ds_desc_t *desc,
-		int n,
+		int nin,
 		void *buffer) {
 
 	int retval = 0;
+	int n = nin - desc->image_number_offset;
 	int block, frame_count, idx;
 	struct eiger_ds_desc_t *eiger_desc = (struct eiger_ds_desc_t*) desc;
 	char data_name[16] = {0};

src/file.h

@@ -17,6 +17,7 @@ struct ds_desc_t {
 	hid_t data_g_id;
 	hsize_t dims[3];
 	int data_width;
+        int image_number_offset;
 	int (*get_pixel_properties)(const struct ds_desc_t*, double*, double*);
 	int (*get_pixel_mask)(const struct ds_desc_t*, int*);
 	int (*get_data_frame)(const struct ds_desc_t*, const int, void*);

src/plugin.c

@@ -125,6 +125,13 @@ void plugin_open(
 		ERROR_JUMP(-4, done, "");
 	}
 
+	data_desc->image_number_offset = 0;
+	char *cenv;
+	cenv = getenv("DURIN_IMAGE_NUMBER_OFFSET");
+	if (cenv!=NULL) {
+	  data_desc->image_number_offset = atoi(cenv);
+	}
+
 	mask_buffer = malloc(data_desc->dims[1] * data_desc->dims[2] * sizeof(int));
 	if (mask_buffer) {
 		retval = data_desc->get_pixel_mask(data_desc, mask_buffer);