font-patcher: Add ratio limit to xy scale

[why]
The powerline glyphs (and only them) undergo a xy scaling, where both
dimensions are maximized into the 'cell'.

Normally cells are taller than wide, and everyting looks fine. But we
have square cells (e.g. 2048 * 2048) with the SymbolsOnly font, and
there might be some self patched font that has similar very-wide (in
comparison to hight) cells.

In these fonts some powerline glyphs look rather ugly. For example the
'half cicles' become very wide and un-round, the triangulars become very
pointy.

[how]
Add a new patch-set attribute 'xy-ratio'. When that is set the vertical
(y) scaling is done as usual but the horizontal (x) scaling is limited
such that the width/height ratio is maximally the attributes value.

For example setting it to 0.75 the height is maximized (as usual) but
the width is maximized to be less then 0.75 times the hight (or as wide
as the cell is, whatever is smaller).

It will work with both, 'xy' and 'pa' scaling, at least theoretically.
It has been only checked where it is used now, i.e. with 'xy'.

A possible overlap is not taken into account.

[note]
The values are taken for this reasons:
- 0.59: This is the original half-circle ratio, higher values make them
        loose the (half) circular appearance
- 0.5:  The half circle lines are more shallow
- 0.7:  The triangulars should not be too pointy (random number)

Fixes: #658

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

font-patcher

@@ -665,16 +665,16 @@ class font_patcher:
             'default': {'align': 'c', 'valign': 'c', 'stretch': 'pa', 'params': {}},
 
             # Arrow tips
-            0xe0b0: {'align': 'l', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.02}},
-            0xe0b1: {'align': 'l', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.02}},
-            0xe0b2: {'align': 'r', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.02}},
-            0xe0b3: {'align': 'r', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.02}},
+            0xe0b0: {'align': 'l', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.02, 'xy-ratio': 0.7}},
+            0xe0b1: {'align': 'l', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.02, 'xy-ratio': 0.7}},
+            0xe0b2: {'align': 'r', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.02, 'xy-ratio': 0.7}},
+            0xe0b3: {'align': 'r', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.02, 'xy-ratio': 0.7}},
 
             # Rounded arcs
-            0xe0b4: {'align': 'l', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.01}},
-            0xe0b5: {'align': 'l', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.01}},
-            0xe0b6: {'align': 'r', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.01}},
-            0xe0b7: {'align': 'r', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.01}},
+            0xe0b4: {'align': 'l', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.01, 'xy-ratio': 0.59}},
+            0xe0b5: {'align': 'l', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.01, 'xy-ratio': 0.5}},
+            0xe0b6: {'align': 'r', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.01, 'xy-ratio': 0.59}},
+            0xe0b7: {'align': 'r', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.01, 'xy-ratio': 0.5}},
 
             # Bottom Triangles
             0xe0b8: {'align': 'l', 'valign': 'c', 'stretch': 'xy', 'params': {'overlap': 0.02}},
@@ -1100,6 +1100,17 @@ class font_patcher:
                 if overlap:
                     scale_ratio_x *= 1 + overlap
                     scale_ratio_y *= 1 + 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
+
                 self.sourceFont[currentSourceFontGlyph].transform(psMat.scale(scale_ratio_x, scale_ratio_y))
 
             # We pasted and scaled now we want to align/move