1 files changed, 69 insertions, 0 deletions
diff --git a/lib/lettering/kerning.py b/lib/lettering/kerning.py
new file mode 100644
index 00000000..920e7d59
--- /dev/null
+++ b/lib/lettering/kerning.py
@@ -0,0 +1,69 @@
+from inkex import NSS
+from lxml import etree
+
+
+class FontKerning(object):
+    """
+    This class reads kerning information from an SVG file
+    """
+    def __init__(self, path):
+        with open(path) as svg:
+            self.svg = etree.parse(svg)
+
+    # horiz_adv_x defines the wdith of specific letters (distance to next letter)
+    def horiz_adv_x(self):
+        # In XPath 2.0 we could use ".//svg:glyph/(@unicode|@horiz-adv-x)"
+        xpath = ".//svg:glyph[@unicode and @horiz-adv-x]/@*[name()='unicode' or name()='horiz-adv-x']"
+        hax = self.svg.xpath(xpath, namespaces=NSS)
+        if len(hax) == 0:
+            return {}
+        return dict(zip(hax[0::2], [int(x) for x in hax[1::2]]))
+
+    # kerning (specific distances of two specified letters)
+    def hkern(self):
+        xpath = ".//svg:hkern[(@u1 or @g1) and (@u1 or @g1) and @k]/@*[contains(name(), '1') or contains(name(), '2') or name()='k']"
+        hkern = self.svg.xpath(xpath, namespaces=NSS)
+        for index, glyph in enumerate(hkern):
+            # fontTools.agl will import fontTools.misc.py23 which will output a deprecation warning
+            # ignore the warning for now - until the library fixed it
+            if index == 0:
+                import warnings
+                with warnings.catch_warnings():
+                    warnings.simplefilter("ignore")
+                    from fontTools.agl import toUnicode
+            if len(glyph) > 1 and not (index + 1) % 3 == 0:
+                glyph_names = glyph.split(",")
+                # the glyph name is written in various languages, second is english. Let's look it up.
+                if len(glyph_names) == 1:
+                    hkern[index] = toUnicode(glyph)
+                else:
+                    hkern[index] = toUnicode(glyph_names[1])
+        k = [int(x) for x in hkern[2::3]]
+        u = [k + v for k, v in zip(hkern[0::3], hkern[1::3])]
+        hkern = dict(zip(u, k))
+        return hkern
+
+    # the space character
+    def word_spacing(self):
+        xpath = "string(.//svg:glyph[@glyph-name='space'][1]/@*[name()='horiz-adv-x'])"
+        word_spacing = self.svg.xpath(xpath, namespaces=NSS) or 26
+        return int(word_spacing)
+
+    # default letter spacing
+    def letter_spacing(self):
+        xpath = "string(.//svg:font[@horiz-adv-x][1]/@*[name()='horiz-adv-x'])"
+        letter_spacing = self.svg.xpath(xpath, namespaces=NSS) or 0
+        return int(letter_spacing)
+
+    # this value will be saved into the json file to preserve it for later font edits
+    # additionally it serves to automatically define the line height (leading)
+    def units_per_em(self, default=100):
+        xpath = "string(.//svg:font-face[@units-per-em][1]/@*[name()='units-per-em'])"
+        units_per_em = self.svg.xpath(xpath, namespaces=NSS) or default
+        return int(units_per_em)
+
+    """
+    def missing_glyph_spacing(self):
+        xpath = "string(.//svg:missing-glyph/@*[name()='horiz-adv-x'])"
+        return float(self.svg.xpath(xpath, namespaces=NSS))
+    """