Allow drivers to specify custom bz3 match threshold

aes4000 detects fewer minutiae and hence returns lower scores.

libfprint/drivers/aes4000.c

@@ -220,6 +220,9 @@ struct fp_img_driver aes4000_driver = {
 	.img_width = 96,
 	.enlarge_factor = 3,
 
+	/* temporarily lowered until image quality improves */
+	.bz3_threshold = 9,
+
 	.init = dev_init,
 	.exit = dev_exit,
 	.capture = capture,

libfprint/fp_internal.h

@@ -127,6 +127,7 @@ struct fp_img_driver {
 	int img_width;
 	int img_height;
 	unsigned int enlarge_factor;
+	int bz3_threshold;
 
 	/* Device operations */
 	int (*init)(struct fp_img_dev *dev, unsigned long driver_data);

libfprint/imgdev.c

@@ -186,12 +186,16 @@ int img_dev_enroll(struct fp_dev *dev, gboolean initial, int stage,
 	return FP_ENROLL_COMPLETE;
 }
 
+#define BOZORTH3_DEFAULT_THRESHOLD 40
+
 static int img_dev_verify(struct fp_dev *dev,
 	struct fp_print_data *enrolled_print)
 {
 	struct fp_img_dev *imgdev = dev->priv;
+	struct fp_img_driver *imgdrv = fpi_driver_to_img_driver(dev->drv);
 	struct fp_img *img;
 	struct fp_print_data *print;
+	int match_score = imgdrv->bz3_threshold;
 	int r;
 
 	r = fpi_imgdev_capture(imgdev, 0, &img);
@@ -209,11 +213,14 @@ static int img_dev_verify(struct fp_dev *dev,
 		return FP_VERIFY_RETRY;
 	}
 
+	if (match_score == 0)
+		match_score = BOZORTH3_DEFAULT_THRESHOLD;
+
 	r = fpi_img_compare_print_data(enrolled_print, print);
 	fp_print_data_free(print);
 	if (r < 0)
 		return r;
-	if (r >= 40)
+	if (r >= match_score)
 		return FP_VERIFY_MATCH;
 	else
 		return FP_VERIFY_NO_MATCH;