Drawing text with a font, using kerning info.

ttf_font_kerning.py

from collections import defaultdict
import wx
from fontTools.pens.wxPen import WxPen
from fontTools.ttLib import TTFont


class MyFrame(wx.Frame):
    def __init__(self, ttfont: TTFont):
        wx.Frame.__init__(self, None, -1, "Font painter")
        self.font = ttfont
        self.prepare_kerning()
        self.Bind(wx.EVT_PAINT, self.on_paint)

    def prepare_kerning(self):
        self.kerning_pairs = defaultdict(int)
        if not "kern" in self.font:
            return
        for kern_table in self.font['kern'].kernTables:
            assert kern_table.version == 0, "kern table version other than 0 not supported"
            self.kerning_pairs.update(kern_table.kernTable)

    def on_paint(self, evt):
        evt.Skip()
        t = "VAVA7FAT"
        dc = wx.PaintDC(self)
        gc = wx.GraphicsContext.Create(dc)

        height = self.GetSize()[1]
        units_per_em = self.font['head'].unitsPerEm
        scale = height / 4 / units_per_em

        m = gc.CreateMatrix()
        m.Translate(0, height // 2)
        m.Scale(scale, -scale)

        cmap = self.font['cmap'].getBestCmap()
        for unicode in t:
            glyph_name = cmap.get(ord(unicode))
            if not glyph_name:
                glyph_name = ".notdef"
            glyph = self.draw_glyph(gc, glyph_name, m, wx.RED_BRUSH)
            m.Translate(glyph.width, 0)

        m = gc.CreateMatrix()
        m.Translate(0, height // 2)
        m.Scale(scale, -scale)

        last = None
        cmap = self.font['cmap'].getBestCmap()
        for unicode in t:
            glyph_name = cmap.get(ord(unicode))
            if not glyph_name:
                glyph_name = ".notdef"
            m.Translate(self.kerning_pairs[last, glyph_name], 0)
            glyph = self.draw_glyph(gc, glyph_name, m, wx.BLACK_BRUSH)
            m.Translate(glyph.width, 0)
            last = glyph_name

    def draw_glyph(self, gc, glyph_name, m, brush):
        glyph = self.font.getGlyphSet()[glyph_name]
        pen = WxPen(self.font.getGlyphSet())
        glyph.draw(pen)
        pen.path.Transform(m)
        gc.SetBrush(brush)
        gc.FillPath(pen.path)
        return glyph


def show_ui(font):
    app = wx.App()
    frame = MyFrame(font)
    frame.Show()
    frame.Maximize(True)
    app.MainLoop()

if "__main__" == __name__:
    show_ui(TTFont("/usr/share/fonts/truetype/liberation2/LiberationSans-Regular.ttf"))