examples: Add sendvirtimg.py script to send a print to virtual_imgdev

With this script it is possible to test libfprint/fprintd without any
hardware device. The image needs to be provides as a PNG with the alpha
channel storing the print data.

See the comment in the file on how the script can be used.

examples/sendvirtimg.py

@@ -0,0 +1,86 @@
+#!/usr/bin/env python3
+
+# This script can be used together with the virtual_imgdev to simulate an
+# image based fingerprint reader.
+#
+# To use, set the FP_VIRTUAL_IMGDEV environment variable for both the
+# libfprint using program (e.g. fprintd) and this script.
+#
+# Usually this would work by adding it into the systemd unit file. The
+# best way of doing so is to create
+#  /etc/systemd/system/fprintd.service.d/fprintd-test.conf
+#
+# [Service]
+# RuntimeDirectory=fprint
+# Environment=FP_VIRTUAL_IMGDEV=/run/fprint/virtimg_sock
+# Environment=G_MESSAGES_DEBUG=all
+# ReadWritePaths=$RUNTIME_DIR
+#
+# After that run:
+#
+#   systemctl daemon-reload
+#   systemctl restart fprintd.service
+#
+# You may also need to disable selinux.
+#
+# Then run this script with e.g.
+# FP_VIRTUAL_IMGDEV=/run/fprint/virtimg_sock ./sendvirtimg.py prints/whorl.png
+
+
+
+import cairo
+import sys
+import os
+import socket
+import struct
+
+if len(sys.argv) == 2:
+    png = cairo.ImageSurface.create_from_png(sys.argv[1])
+
+    # Cairo wants 4 byte aligned rows, so just add a few pixel if necessary
+    w = png.get_width()
+    h = png.get_height()
+    w = (w + 3) // 4 * 4
+    h = (h + 3) // 4 * 4
+    img = cairo.ImageSurface(cairo.Format.A8, w, h)
+    cr = cairo.Context(img)
+
+    cr.set_source_rgba(1, 1, 1, 1)
+    cr.paint()
+
+    cr.set_source_rgba(0, 0, 0, 0)
+    cr.set_operator(cairo.OPERATOR_SOURCE)
+
+    cr.set_source_surface(png)
+    cr.paint()
+else:
+    sys.stderr.write('You need to pass a PNG with an alpha channel!\n')
+    sys.exit(1)
+
+def write_dbg_img():
+    dbg_img_rgb = cairo.ImageSurface(cairo.Format.RGB24, img.get_width(), img.get_height())
+    dbg_cr = cairo.Context(dbg_img_rgb)
+    dbg_cr.set_source_rgb(0, 0, 0)
+    dbg_cr.paint()
+    dbg_cr.set_source_rgb(1, 1, 1)
+    dbg_cr.mask_surface(img, 0, 0)
+
+    dbg_img_rgb.write_to_png('/tmp/test.png')
+
+#write_dbg_img()
+
+# Send image through socket
+sockaddr = os.environ['FP_VIRTUAL_IMGDEV']
+
+sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+sock.connect(sockaddr)
+
+mem = img.get_data()
+mem = mem.tobytes()
+assert len(mem) == img.get_width() * img.get_height()
+
+encoded_img = struct.pack('ii', img.get_width(), img.get_height())
+encoded_img += mem
+
+sock.sendall(encoded_img)
+