From cd09cbab68d96c4c59fea486fa9f6d795419e7b1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Laura=20Kl=C3=BCnder?= <laura@codingcatgirl.de>
Date: Fri, 20 Oct 2017 22:37:54 +0200
Subject: [PATCH] take shortcut in get_png if this is an empty tile rendering

---
 src/c3nav/mapdata/tasks.py     | 1 +
 src/c3nav/mapdata/utils/svg.py | 9 +++++++++
 2 files changed, 10 insertions(+)

diff --git a/src/c3nav/mapdata/tasks.py b/src/c3nav/mapdata/tasks.py
index 294d4877..0274a91c 100644
--- a/src/c3nav/mapdata/tasks.py
+++ b/src/c3nav/mapdata/tasks.py
@@ -1,4 +1,5 @@
 import os
+
 from django.conf import settings
 
 from c3nav.celery import app
diff --git a/src/c3nav/mapdata/utils/svg.py b/src/c3nav/mapdata/utils/svg.py
index 7c6fc000..135c96f4 100644
--- a/src/c3nav/mapdata/utils/svg.py
+++ b/src/c3nav/mapdata/utils/svg.py
@@ -85,8 +85,17 @@ class SVGImage:
         result += '</svg>'
         return result
 
+    empty_tile = (b'\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR\x00\x00\x01\x00\x00\x00\x01\x00\x01\x03\x00\x00\x00f\xbc:%\x00'
+                  b'\x00\x00\x03PLTE\x00\x00\x00\xa7z=\xda\x00\x00\x00\x01tRNS\x00@\xe6\xd8f\x00\x00\x00\x1fIDATh\xde'
+                  b'\xed\xc1\x01\r\x00\x00\x00\xc2\xa0\xf7Om\x0e7\xa0\x00\x00\x00\x00\x00\x00\x00\x00\xbe\r!\x00\x00'
+                  b'\x01\x7f\x19\x9c\xa7\x00\x00\x00\x00IEND\xaeB`\x82')
+
     def get_png(self, f=None):
         # render the image to png. returns bytes if f is None, otherwise it calls f.write()
+
+        if self.get_dimensions_px(buffer=False) == (256, 256) and not self.g:
+            return self.empty_tile
+
         if settings.SVG_RENDERER == 'rsvg':
             # create buffered surfaces
             buffered_surface = cairocffi.SVGSurface(None, *(int(i) for i in self.get_dimensions_px(buffer=True)))