font-patcher: Correct overlap

[why]
The overlap formula seems to be off sometimes. Although the shift is
correct (and thus the number of 'pixels' that overlap), but the non
overlapping part of the glyph is often not as wide as expected, off by
up to some percent.

[how]
The formula is too simple. It just calculates an additional scale factor
on top of the already existing factor. To get it 'pixel perfect' we need
to calculate first how much the glyph fills the cell - because we want
the overlap to be in 'cell percent' and not 'glyph percent'. That might
be sometimes the same (if the cell is filled completely), but usually it
is not completely full, and that means the overlap will be smaller than
intended.

[note]
To get the current glyph bounding box we pull some lines up in the code
that get the 'dim' variable.

Also use float constants to calculate with float variables.

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

font-patcher

@@ -1116,17 +1116,18 @@ class font_patcher:
 
             overlap = sym_attr['params'].get('overlap')
 
-            if scale_ratio_x != 1 or scale_ratio_y != 1:
+            if scale_ratio_x != 1.0 or scale_ratio_y != 1.0:
+                if glyph_scale_data is not None and glyph_scale_data[1] is not None:
+                    dim = glyph_scale_data[1]
+                else:
+                    dim = sym_dim
                 if overlap:
-                    scale_ratio_x *= 1 + overlap
-                    scale_ratio_y *= 1 + overlap
+                    scale_ratio_x *= 1.0 + (self.font_dim['width'] / (dim['width'] * scale_ratio_x)) * overlap
+                    scale_ratio_y *= 1.0 + (self.font_dim['width'] / (dim['width'] * scale_ratio_y)) * overlap
+
                 # Size in x to size in y ratio limit (to prevent over-wide glyphs)
                 xy_ratio_max = sym_attr['params'].get('xy-ratio')
                 if (xy_ratio_max):
-                    if glyph_scale_data is not None and glyph_scale_data[1] is not None:
-                        dim = glyph_scale_data[1]
-                    else:
-                        dim = sym_dim
                     xy_ratio = dim['width'] * scale_ratio_x / (dim['height'] * scale_ratio_y)
                     if xy_ratio > xy_ratio_max:
                         scale_ratio_x = scale_ratio_x * xy_ratio_max / xy_ratio