doc/usman: workaround: wrong viewbox for dot-generated SVG figures

See "Some figures in the Simulation Manual appear to be zoomed to their top-left corner"
#1048

Since the viewBox correction factor differs from figure to figure, this
fix is not perfect. factor=2.0 seems to be fine for most figures, and
only seriously off (too much) for one.

Both web and pdf renderings look ok.

doc/src/manual/Makefile

@@ -29,6 +29,7 @@ pdf: $(ALLTEX) $(PDFPICS) figures/*.png cover.pdf
 
 %.svg: %.dot
 	$(DOT) -Tsvg $< >$@
+	python3 tools/update-svg-viewBox-after-dot.py $@ 2.0
 
 # --- generating html ---
 

doc/src/manual/tools/update-svg-viewBox-after-dot.py

@@ -0,0 +1,26 @@
+# In Graphviz 2.x, dot-generated SVGs are faulty (view box too small), this script fixes it.
+# See https://github.com/omnetpp/omnetpp/issues/1048, https://gitlab.com/graphviz/graphviz/-/issues/1406
+
+import sys
+import re
+
+if len(sys.argv) not in [2, 3]:
+    print(f"Usage: python {sys.argv[0]} input.svg [viewbox-enhancing-factor]")
+    sys.exit(1)
+
+input_file = sys.argv[1]
+factor = float(sys.argv[2]) if len(sys.argv) == 3 else 2.0
+
+with open(input_file, "r") as file:
+    svg_text = file.read()
+
+if re.search(r"Generated by graphviz version 2\.\d+\.\d+", svg_text):
+    # Enlarge viewBox
+    svg_text = re.sub(r'viewBox="([^"]+)"', lambda match: 'viewBox="' + ' '.join(str(float(value) * factor) for value in match.group(1).split()) + '"', svg_text)
+
+    # Save the modified SVG back to the same file
+    with open(input_file, "w") as file:
+        file.write(svg_text)
+    print(f"ViewBox modified and saved to {input_file}")
+else:
+    print(f"Graphviz is NOT of version 2.x, ViewBox is probably OK, not touching it")