Use a sans-serif math font

pgfplots uses math fonts for graphs ticks... and it looks weird when
building sans serif.

Not sure Fira is necessarily a great choice with open-sans but we have
very little math so that should do...

book/book_sans_serif.tex

@@ -1,2 +1,4 @@
 \def\isaccessible{1}
-\input{book.tex}
+% We have to use a symlink to book.tex to prevent tex4ebook to load book.ht4
+% before loading any other package and create conflicts
+\input{sourdough_book.tex}

book/makefile

@@ -10,7 +10,7 @@ REDUCE_PIC := -resize '800x800>' \
 	    -strip -interlace Plane  -gaussian-blur 0.05 -quality 85\% \
 	    -set colorspace Gray -separate -evaluate-sequence Mean
 REDUCE_PIC_COLOR := -quality 80\%
-RSYNC := rsync -au --exclude 'book.epub' --exclude '*.jpg'
+RSYNC := rsync -au --exclude 'book_sans_serif.epub' --exclude '*.jpg'
 GIT := git --no-pager
 SPELL_CHECK := hunspell -t -l -d en_US
 EPUBSIZE := `du -sb epub/low_res_book.epub | cut -f1`
@@ -118,10 +118,10 @@ epub/%.epub: %.tex $(ebook_src) cover/cover-page.xbb
 	$(EBOOK) $<
 
 copy_ebook_files: build_ebook
-	$(RSYNC) --exclude '*.png' epub_build/book-epub/ bw-book-epub/
+	$(RSYNC) --exclude '*.png' epub_build/book_sans_serif-epub/ bw-book-epub/
 
 copy_ebook_files_low_res: build_ebook
-	$(RSYNC) epub_build/book-epub/ low-res-book-epub/
+	$(RSYNC) epub_build/book_sans_serif-epub/ low-res-book-epub/
 
 # We do not convert SVG to B&W or lower res for now as they are super small
 # anyway
@@ -218,7 +218,7 @@ build_serif_pdf: book_serif/book.pdf
 
 build_sans_serif_pdf: book_sans_serif/book_sans_serif.pdf
 
-build_ebook: epub/book.epub
+build_ebook: epub/book_sans_serif.epub
 
 build_bw_ebook: epub/bw_book.epub
 
@@ -317,10 +317,10 @@ release_booklet: build_booklet | release
 
 # Website stuff
 .PHONY: html website
-$(website_dir)/book.html: $(website_src) cover/cover-page.xbb
-	$(WEBSITE) -d $(website_dir) book.tex
+$(website_dir)/book_sans_serif.html: $(website_src) cover/cover-page.xbb
+	$(WEBSITE) -d $(website_dir) book_sans_serif.tex
 
-html: $(website_dir)/book.html
+html: $(website_dir)/book_sans_serif.html
 	cp $< $(website_dir)/index.html
 
 # Because packages will be installed in hard to predict places use a file as
@@ -346,7 +346,7 @@ quick_booklet:
 	$(LATEX) -e '$$max_repeat=1' -halt-on-error -output-directory=booklet booklet.tex
 
 quick_ebook: cover/cover-page.xbb  # run latex only once no biber, ref etc...
-	$(EBOOK) --mode draft book.tex
+	$(EBOOK) --mode draft book_sans_serif.tex
 
 show_tools_version:  # Show version of tools used on the build machine
 	- $(GIT) log -1 --pretty=%B

book/sourdough.sty

@@ -52,8 +52,9 @@
 \DeclareRobustCommand\sbseries{\fontseries{sb}\selectfont}
 % Fonts for accessibility
 \ifdefined\isaccessible
-    \setmainfont{Open Sans}[
-    Scale=MatchLowercase]
+    \usepackage[mathrm=sym]{unicode-math}
+    \setmathfont{Fira Math}[Scale=MatchLowercase]
+    \setmainfont{Open Sans}[Scale=MatchLowercase]
 \else
     \setmainfont{TeX Gyre Pagella}[Scale=1.0] % Or Palatino Linotype, etc.
     % TODO not available on github CI

book/sourdough_book.tex

@@ -0,0 +1 @@
+book.tex

website/modify_build.rb

@@ -79,7 +79,7 @@ class ModifyBuild
   end
 
   def is_cover_page?(filename)
-    ["book.html", "index.html"].any? do |name|
+    ["book_sans_serif.html", "index.html"].any? do |name|
       filename.include?(name)
     end
   end
@@ -126,8 +126,8 @@ class ModifyBuild
   def validate_file(text)
     doc = build_doc(text)
     stylesheets = doc.css("link[rel='stylesheet']").map{|attr| attr["href"] }
-    has_all_styles = %w(book.css style.css).all? { |required_stylesheet| stylesheets.include?(required_stylesheet) }
-    raise InvalidWebsiteFormat.new("No style tag style.css found in the website") unless has_all_styles
+    has_all_styles = %w(book_sans_serif.css style.css).all? { |required_stylesheet| stylesheets.include?(required_stylesheet) }
+    raise InvalidWebsiteFormat.new("No style tag style.css or book_sans_serif.css found in the website") unless has_all_styles
     true
   end
 
@@ -456,7 +456,7 @@ class ModifyBuild
     doc.to_html
   end
 
-  # Takes a name like "static_website_html/book.html" and returns "book.html"
+  # Takes a name like "static_website_html/book_sans_serif.html" and returns "book_sans_serif.html"
   def extract_file_from_path(filename)
     result = filename.split("/")
     return filename if result.length == 1
@@ -483,6 +483,7 @@ class ModifyBuild
     index_text = "The Sourdough Framework goes beyond just recipes and provides a solid knowledge foundation, covering the science of sourdough, the basics of bread making, and advanced techniques for achieving the perfect sourdough bread at home."
     data = {
       "book.html" => index_text,
+      "book_sans_serif.html" => index_text,
       "index.html" => index_text
     }
     data[filename]
@@ -526,12 +527,6 @@ class ModifyBuild
       el["href"] == ""
     end
 
-    # Special case for index page
-    #if ["index.html", "book.html"].include?(filename)
-    #  doc.css(".menu-items .chapterToc.home-link")[0].add_class("selected")
-    #  return doc.to_html
-    #end
-
     # Special case for the flowcharts page which is added by us to the menu.
     # This needs to be done for future manually added pages too
     if "listoflocname.html" == filename
@@ -561,7 +556,7 @@ class ModifyBuild
   def add_canonical_for_duplicates(text, filename)
     # Only applies to book.html which is a duplicate for index.html. The file
     # is still needed though for proper display.
-    canonical_pages = ["book.html", "index.html"]
+    canonical_pages = ["book_sans_serif.html", "index.html"]
     return text unless canonical_pages.include?(filename)
     doc = build_doc(text)
     head = doc.css("head")[0]