Switch to Cairo-based SVG 2 PDF converter

We previously used a (terribly nice) Makefile to invoke Inkscape to
convert our SVG images to PDF. This was not always reliable. Copying the
Cairo-based SVG2PDF Sphinx extension from OpTiMSoC is much nicer.

Author: imphil

Makefile

@@ -13,14 +13,6 @@ SPHINXPROJ    = OpenSoCDebug
 SOURCEDIR     = src
 BUILDDIR      = build
 
-SVG2PDF       = inkscape
-SVG2PDF_FLAGS =
-
-# Build a list of SVG files to convert to PDFs
-IMAGES_SVG_REL := $(shell find $(SOURCEDIR) -iname '*.svg' -printf '%P\n')
-IMAGES_PDF := $(addprefix $(BUILDDIR)/,$(IMAGES_SVG_REL:.svg=.pdf))
-
-
 # Put it first so that "make" without argument is like "make help".
 help: .venv
 	@$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
@@ -31,21 +23,6 @@ help: .venv
 	.venv/bin/pip -q install --upgrade pip
 	.venv/bin/pip -q install -r requirements.txt
 
-.SECONDEXPANSION:
-$(IMAGES_PDF): %.pdf : $$(subst $$(BUILDDIR),$$(SOURCEDIR),%).svg
-	mkdir -p $(@D)
-	$(SVG2PDF) -f $< -A $@
-
-# Convert images from SVG to PDF for LaTeX PDF output
-images-pdf: $(IMAGES_PDF)
-
-# Convert images to PDF before running the LaTeX PDF build
-latexpdf: .venv Makefile images-pdf
-	@$(SPHINXBUILD) -M latexpdf "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
-
-clean-images:
-	-rm $(IMAGES_PDF)
-
 clean: .venv Makefile clean-images
 	@$(SPHINXBUILD) -M clean "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
 

requirements.txt

@@ -1,3 +1,4 @@
 Sphinx>=1.6
 breathe
 sphinx-rtd-theme
+cairosvg

sphinx/cairosvgconverter.py

@@ -0,0 +1,38 @@
+# -*- coding: utf-8 -*-
+"""
+"""
+from sphinx.errors import ExtensionError
+from sphinx.locale import _
+from sphinx.transforms.post_transforms.images import ImageConverter
+from sphinx.util import logging
+from sphinx.util.osutil import ENOENT, EPIPE, EINVAL
+from cairosvg import svg2pdf
+
+logger = logging.getLogger(__name__)
+
+class CairoSvgConverter(ImageConverter):
+    conversion_rules = [
+        ('image/svg+xml', 'application/pdf'),
+    ]
+
+    def is_available(self):
+        # type: () -> bool
+        return True
+
+    def convert(self, _from, _to):
+        # type: (unicode, unicode) -> bool
+        """Converts the image to expected one."""
+        svg2pdf(url=_from, write_to=_to)
+
+        return True
+
+
+def setup(app):
+    # type: (Sphinx) -> Dict[unicode, Any]
+    app.add_post_transform(CairoSvgConverter)
+
+    return {
+        'version': 'builtin',
+        'parallel_read_safe': True,
+        'parallel_write_safe': True,
+    }

src/conf.py

@@ -34,6 +34,7 @@
   'sphinx.ext.todo',
   'sphinx.ext.autodoc',
   'sphinx.ext.mathjax',
+  'cairosvgconverter',
 ]
 
 # Add any paths that contain templates here, relative to this directory.