[Maposmatic-dev] [PATCH] Generate nice thumbnails for multi-page renderings

[Thomas Petazzoni]

For multi-page renderings, the thumbnail was useless: it was the last
page of the index. Instead, we create with ImageMagick a small
thumbnail thats displays the cover page and overview page of the
multi-page PDF. We take into account landscape/portrait renderings to
combine those two images into a single thumbnail with a good ratio.

We directly use subprocess to run the ImageMagick commands, because
the Python ImageMagick API is so poorly documented that after spending
several hours trying to figure out which method to use, switching to
subprocess with ImageMagick commands turned out to be a more
reasonable solution.

Signed-off-by: Thomas Petazzoni <address@hidden>
---
 INSTALL           |    5 ++++-
 scripts/render.py |   40 +++++++++++++++++++++++++++++++++++-----
 2 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/INSTALL b/INSTALL
index b01a1ee..b1bafc9 100644
--- a/INSTALL
+++ b/INSTALL
@@ -23,10 +23,13 @@ MapOSMatic depends on :
 
  * JSON (any python-*json package should work).
 
+ * ImageMagick, for rendering the thumbnails of multi-page maps
+
 On an debian/ubuntu installation, the following should be enough:
 
   sudo aptitude install python-django python-psycopg2 \
-          python-feedparser python-imaging gettext
+          python-feedparser python-imaging gettext \
+          imagemagick
 
 You will also most likely need a working PostGIS installation for the
 entire pipeline to run. See the INSTALL documentation of OcitySMap for
diff --git a/scripts/render.py b/scripts/render.py
index e3a78b5..4a975fc 100755
--- a/scripts/render.py
+++ b/scripts/render.py
@@ -28,6 +28,7 @@ import logging
 import os
 import sys
 import threading
+import subprocess
 
 import ocitysmap2
 import ocitysmap2.coords
@@ -135,6 +136,38 @@ class JobRenderer(threading.Thread):
             ctypes.pythonapi.PyThreadState_SetAsyncExc(self.__get_my_tid(), 0)
             raise SystemError("PyThreadState_SetAsync failed")
 
+    def _gen_thumbnail(self, prefix, paper_width_mm, paper_height_mm):
+        l.info('Creating map thumbnail...')
+        if self.job.layout == "multi_page":
+            # Depending on whether we're rendering landscape or
+            # portrait, adapt how the tiling is done.
+            if paper_width_mm > paper_height_mm:
+                tile = "1x2"
+            else:
+                tile = "2x1"
+
+            # With the 'montage' command from ImageMagick, create an
+            # image with the first two pages of the PDF (cover page
+            # and overview page).
+            montage_cmd = [ "montage", "-tile", tile, "%s.pdf[0]" % prefix,
+                            "%s.pdf[2]" % prefix, "-geometry", "+10+10",
+                            "-shadow", "%s%s" % (prefix, THUMBNAIL_SUFFIX) ]
+            ret = subprocess.call(montage_cmd)
+            if ret != 0:
+                return
+
+            # And now scale it to the normal thumbnail size
+            mogrify_cmd = [ "mogrify", "-scale", "200x200",
+                            "%s%s" % (prefix, THUMBNAIL_SUFFIX) ]
+            ret = subprocess.call(mogrify_cmd)
+            if ret != 0:
+                return
+        else:
+            if 'png' in RENDERING_RESULT_FORMATS:
+                img = Image.open(prefix + '.png')
+                img.thumbnail((200, 200), Image.ANTIALIAS)
+                img.save(prefix + THUMBNAIL_SUFFIX)
+
     def run(self):
         """Renders the given job, encapsulating all processing errors and
         exceptions.
@@ -188,11 +221,8 @@ class JobRenderer(threading.Thread):
                             RENDERING_RESULT_FORMATS, prefix)
 
             # Create thumbnail
-            if 'png' in RENDERING_RESULT_FORMATS:
-                l.info('Creating map thumbnail...')
-                img = Image.open(prefix + '.png')
-                img.thumbnail((200, 200), Image.ANTIALIAS)
-                img.save(prefix + THUMBNAIL_SUFFIX)
+            self._gen_thumbnail(prefix, config.paper_width_mm,
+                                config.paper_height_mm)
 
             self.result = RESULT_SUCCESS
             l.info("Finished rendering of job #%d." % self.job.id)
-- 
1.7.4.1