Add thumbnail templating code

common/common/images.py

@@ -0,0 +1,46 @@
+
+import os
+from io import BytesIO
+
+from PIL import Image
+
+# The region of the frame image to place on the template.
+# Format is (top_left_x, top_left_y, bottom_right_x, bottom_right_y).
+# The frame is scaled to the size of the template before this is done.
+FRAME_CROP = None # no crop
+
+# The location in the template to place the frame image after cropping.
+# Format is (x, y) of top-left corner.
+FRAME_LOCATION = (0, 90)
+
+
+def compose_thumbnail_template(base_dir, template_name, frame_data):
+	template_path = os.path.join(base_dir, "thumbnail_templates", f"{template_name}.png")
+	template = Image.open(template_path)
+	# PIL can't load an image from a byte string directly, we have to pretend to be a file
+	frame = Image.open(BytesIO(frame_data))
+
+	# The parameters of how we overlay the template are hard-coded for now.
+	# We can make this configurable later if needed.
+
+	# Create a new blank image of the same size as the template
+	result = Image.new('RGBA', template.size)
+	# If the frame is not the same size, scale it so it is.
+	# For choice of rescaling filter, pick LANCZOS (aka. ANTIALIAS) as it is highest quality
+	# and we don't really care about performance.
+	if frame.size != template.size:
+		frame = frame.resize(template.size, Image.LANCZOS)
+	# Insert the frame at the desired location and cropping
+	if FRAME_CROP is not None:
+		frame = frame.crop(FRAME_CROP)
+	result.paste(frame, FRAME_LOCATION)
+	# Place the template "on top", letting the frame be seen only where the template's alpha
+	# lets it through.
+	result.alpha_composite(template)
+
+	buf = BytesIO()
+	# PIL can't save an image to a byte string directly, we have to pretend to write it to
+	# a file, rewind the file, then read it again.
+	result.save(buf, format='png')
+	buf.seek(0)
+	return buf.read()

cutter/setup.py

@@ -7,6 +7,7 @@ setup(
 	install_requires = [
 		"argh",
 		"gevent",
+		"Pillow", # for thumbnail templating
 		"prometheus-client",
 		"psycogreen",
 		"psycopg2",