graphics: Add kerning for text generator.

Adjust character positions so that some pairs of characters can fit
more closely together.

graphics/text/config.py

@@ -33,6 +33,41 @@
 # that are generated, and the text to show in each one.
 #
 
+# Adjustments for character position based on character pairs. Some
+# pairs of characters can fit more snugly together, which looks more
+# visually appealing. This is highly dependent on the font graphics,
+# and if the font is changed this probably needs to be redone.
+
+FONT_KERNING_RULES = {
+	# Right character fits under left character:
+	r'p[aj\.]': -3,
+	r'P[a\.]': -4,
+	r'[PVW][AJj\.]': -4,
+	r't[ajJ\.]': -4,
+	r'f[aj\.]': -2,
+
+	# Some capital letters have overhangs that the 'lower case'
+	# characters can fit under:
+	r'C[Ja-z\.]': -2,
+	r'F[Ja-z\.]': -3,
+	r'T[Ja-z\.]': -5,
+	r'W[Ja-z\.]': -2,
+	r'S[Ja-z\.]': -1,
+	r'V[a-z\.]': -3,
+
+	# Left character fits under right character:
+	r'[alAL][ty479]': -3,
+	r'a[vwVW]': -2,
+	r'A[VW]': -3,
+	r'A[vw]': -2,
+	r'r[ty479]': -2,
+	r'[vwVW][Aa]': -2,
+	r'[Yypv][jJ]': -2,
+
+	# Extra space needed:
+	r'[OUu][Pp]': +1,
+}
+
 white_graphics = {
 	'wibp1': 'P1',
 	'wibp2': 'P2',

graphics/text/textgen

@@ -58,7 +58,7 @@ BACKGROUND_COLOR = '#00ffff'
 FONT_HEIGHT = 16
 
 # Width of a space character in pixels.
-SPACE_WIDTH = 14
+SPACE_WIDTH = 10
 
 # Output from 'identify' looks like this:
 #  fontchars/font033.gif GIF 9x16 9x16+0+0 8-bit sRGB 32c 194B 0.000u 0:00.000
@@ -93,10 +93,19 @@ def invoke_command(command):
 	return subprocess.call(command)
 
 class Font(object):
-	def __init__(self, fontdir):
+	def __init__(self, fontdir, kerning_table={}):
 		self.fontdir = fontdir
+		self.kerning_table = self.compile_kerning_table(kerning_table)
 		self.get_font_widths()
 
+	def compile_kerning_table(self, kerning_table):
+		"""Given a dictionary of kerning patterns, compile Regexps."""
+
+		result = {}
+		for pattern, adjust in kerning_table.items():
+			result[re.compile(pattern)] = adjust
+		return result
+
 	def get_font_widths(self):
 		charfiles = glob('%s/font*.gif' % self.fontdir)
 		self.char_widths = {}
@@ -116,20 +125,37 @@ class Font(object):
 	def char_filename(self, c):
 		return '%s/font%03d.gif' % (self.fontdir, ord(c))
 
+	def kerning_adjust(self, char_1, char_2):
+		"""Get kerning adjustment for pair of characters.
+
+		Zero means no adjustment. A negative value adjusts to the
+		left and a positive value adjusts to the right.
+		"""
+		for pattern, adjust in self.kerning_table.items():
+			if pattern.match(char_1 + char_2):
+				return adjust
+		else:
+			return 0
+
 	def iterate_char_positions(self, text):
 		"""Iterate over characters in string, yielding character with
 		   position it should be placed at in the output file.
 		"""
 		x = 0
+		last_c = ' '
 		for c in text:
 			if c == ' ':
 				x += SPACE_WIDTH
-			if c not in self:
-				continue
-			yield c, x
 
-			# Characters overlap by one pixel.
-			x += self.char_width(c) - 1
+			if c in self:
+				x += self.kerning_adjust(last_c, c)
+
+				yield c, x
+
+				# Characters overlap by one pixel.
+				x += self.char_width(c) - 1
+
+			last_c = c
 
 		# We need to add back the missing pixel from the right side
 		# of the last char.
@@ -198,7 +224,7 @@ def generate_graphics(graphics, color=COLOR_WHITE):
 		print("# %s.gif: '%s'" % (name, text))
 		font.render_text(text, '%s.gif' % name, color=color)
 
-font = Font('fontchars')
+font = Font('fontchars', kerning_table=FONT_KERNING_RULES)
 
 generate_graphics(red_graphics, COLOR_RED)
 generate_graphics(blue_graphics, COLOR_BLUE)