lib: Add fp_driver_supports_imaging()

So we don't need to open a device before checking whether it supports
imaging.

doc/libfprint-sections.txt

@@ -40,6 +40,7 @@ fp_driver_get_name
 fp_driver_get_full_name
 fp_driver_get_driver_id
 fp_driver_get_scan_type
+fp_driver_supports_imaging
 </SECTION>
 
 <SECTION>

libfprint/fpi-core.c

@@ -579,6 +579,24 @@ API_EXPORTED enum fp_scan_type fp_driver_get_scan_type(struct fp_driver *drv)
 	return drv->scan_type;
 }
 
+/**
+ * fp_driver_supports_imaging:
+ * @drv: the driver
+ *
+ * Determines if a driver has imaging capabilities. If a driver has imaging
+ * capabilities you are able to perform imaging operations such as retrieving
+ * scan images using fp_dev_img_capture(). However, not all drivers support
+ * imaging devices – some do all processing in hardware. This function will
+ * indicate which class a device in question falls into.
+ *
+ * Returns: 1 if the device is an imaging device, 0 if the device does not
+ * provide images to the host computer
+ */
+API_EXPORTED int fp_driver_supports_imaging(struct fp_driver *drv)
+{
+	return drv->capture_start != NULL;
+}
+
 /**
  * fp_dev_supports_imaging:
  * @dev: the fingerprint device

libfprint/fprint.h

@@ -130,6 +130,7 @@ const char *fp_driver_get_name(struct fp_driver *drv);
 const char *fp_driver_get_full_name(struct fp_driver *drv);
 uint16_t fp_driver_get_driver_id(struct fp_driver *drv);
 enum fp_scan_type fp_driver_get_scan_type(struct fp_driver *drv);
+int fp_driver_supports_imaging(struct fp_driver *drv);
 
 /* Device discovery */
 struct fp_dscv_dev **fp_discover_devs(void);