renderdiff: add viewer for image differences (#8768)

- Modify the compare script to output more details of a
   comparison. This will include the source/golden directory,
   the comparison directory (the new renderings), and a file
   path to difference images if the golden does not match
   the rendered image.
 - The image_diff script can now output a TIFF that is the
   difference of two input TIFFs.
 - Add a viewer for examining the differences between rendered
   output and golden images.
 - The viewer consists of a simple server of web API endpoints
   for querying difference results (along with rendered images
   in TIFF).
 - And a web-based (html + lit-element) UI for looking at the
   rendered images and differences.

test/renderdiff/src/viewer.py

@@ -0,0 +1,81 @@
+# Copyright (C) 2025 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import os
+import sys
+import flask
+import pathlib
+import json
+
+from utils import ArgParseImpl
+
+from flask import Flask, request, make_response, send_from_directory
+
+DIR = pathlib.Path(__file__).parent.absolute()
+HTML_DIR = os.path.join(DIR, "viewer_html")
+
+def _create_app(config):
+  app = Flask(__name__)
+
+  client_config = config.copy()
+  base_dir = client_config['base_dir']
+  comparison_dir = client_config['comparison_dir']
+  diff_dir = client_config['diff_dir']
+
+  del client_config['base_dir']
+  del client_config['comparison_dir']
+  del client_config['diff_dir']
+
+  @app.route('/r/', methods=['GET'])
+  def get_r():
+    return json.dumps(client_config)
+
+  @app.route('/g/<path:filepath>', methods=['GET'])
+  def get_g(filepath):
+    return send_from_directory(base_dir, filepath)
+
+  @app.route('/d/<path:filepath>', methods=['GET'])
+  def get_d(filepath):
+    return send_from_directory(diff_dir, filepath)
+
+  @app.route('/c/<path:filepath>', methods=['GET'])
+  def get_c(filepath):
+    return send_from_directory(comparison_dir, filepath)
+
+  @app.route('/<path:filepath>')
+  def get_static_file(filepath):
+    return send_from_directory(HTML_DIR, filepath)
+
+  @app.route('/')
+  def get_index():
+    return send_from_directory(HTML_DIR, 'index.html')
+
+  app.url_map.strict_slashes = False
+  return app
+
+if __name__ == '__main__':
+  PORT = 8901
+  parser = ArgParseImpl()
+  parser.add_argument('--diff', help='Diff directory', required=True)
+  args, _ = parser.parse_known_args(sys.argv[1:])
+
+  with open(os.path.join(args.diff, 'compare_results.json'), 'r') as f:
+    config = json.loads(f.read())
+  config['diff_dir'] = os.path.abspath(args.diff)
+
+  app = _create_app(config)
+  from waitress import serve
+
+  print(f'Point your browser to http://localhost:{PORT} to see the diff results')
+  serve(app, host="127.0.0.1", port=PORT)