font-patcher: Issue warning if symbol scaling fails monospace goal

[why]
Sometimes fonts patched with --mono are not recognized as monospaced
fonts.

One reason can be that the inserted glyphs are too wide. This will show
in the end in the font's advanceWidthMax property which is not congruent
to the normal font width.

[how]
After all the scaling and jiggling we double check if the new glyph
already in the to-be-patched is not wider than our design goal for the
width. Normally one would expect that this always holds.

An exemption could be if we insert ligatures, that are two spaces wide.
But at the moment we can not anyhow (because there is no way to add
information to the ligature tables right now).

If a glyph is wider a warning is issued.

No warning is issued if the glyph shall have some overlap. That overlap
is taken into account of this check.

Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>

font-patcher

@@ -770,10 +770,15 @@ class font_patcher:
                 # Currently stretching vertically for both monospace and double-width
                 scale_ratio_y = self.font_dim['height'] / sym_dim['height']
 
+            if 'overlap' in sym_attr['params']:
+                overlap = sym_attr['params']['overlap']
+            else:
+                overlap = 0
+
             if scale_ratio_x != 1 or scale_ratio_y != 1:
-                if 'overlap' in sym_attr['params']:
-                    scale_ratio_x *= 1 + sym_attr['params']['overlap']
-                    scale_ratio_y *= 1 + sym_attr['params']['overlap']
+                if overlap != 0:
+                    scale_ratio_x *= 1 + overlap
+                    scale_ratio_y *= 1 + overlap
                 self.sourceFont[currentSourceFontGlyph].transform(psMat.scale(scale_ratio_x, scale_ratio_y))
 
             # Use the dimensions from the newly pasted and stretched glyph
@@ -797,8 +802,8 @@ class font_patcher:
                     # Right align
                     x_align_distance += self.font_dim['width'] - sym_dim['width']
 
-            if 'overlap' in sym_attr['params']:
-                overlap_width = self.font_dim['width'] * sym_attr['params']['overlap']
+            if overlap != 0:
+                overlap_width = self.font_dim['width'] * overlap
                 if sym_attr['align'] == 'l':
                     x_align_distance -= overlap_width
                 if sym_attr['align'] == 'r':
@@ -817,6 +822,13 @@ class font_patcher:
             # does not overlap the bearings (edges)
             self.remove_glyph_neg_bearings(self.sourceFont[currentSourceFontGlyph])
 
+            # Check if the inserted glyph is scaled correctly for monospace
+            if self.args.single:
+                (xmin, _, xmax, _) = self.sourceFont[currentSourceFontGlyph].boundingBox()
+                if int(xmax - xmin) > self.font_dim['width'] * (1 + overlap):
+                    print("\n  Warning: Scaled glyph U+{:X} wider than one monospace width ({} / {} (overlap {}))".format(
+                        currentSourceFontGlyph, int(xmax - xmin), self.font_dim['width'], overlap))
+
         # end for
 
         if self.args.quiet is False or self.args.progressbars: