[fb] Add default hard-coded font

For the fb driver to have a font before loading from disk is available,
create a hard-coded font as a byte array.

To create this, added a new scripts/psf_to_cpp.py which also refactored
out much of scripts/parse_font.py into a new shared module
scripts/fontpsf.py.

scripts/fontpsf.py

@@ -0,0 +1,75 @@
+_MAGIC = (0x72, 0xb5, 0x4a, 0x86)
+_VERSION = 0
+
+class PSF2:
+    from collections import namedtuple
+    Header = namedtuple("PSF2Header",
+        ["version", "offset", "flags", "count", "charsize", "height", "width"])
+
+    def __init__(self, filename, header, data):
+        self.__filename = filename
+        self.__header = header
+        self.__data = data
+
+    data = property(lambda self: self.__data)
+    header = property(lambda self: self.__header)
+    count = property(lambda self: self.__header.count)
+    charsize = property(lambda self: self.__header.charsize)
+    dimension = property(lambda self: (self.__header.width, self.__header.height))
+    filename = property(lambda self: self.__filename)
+
+    @classmethod
+    def load(cls, filename):
+        from os.path import basename
+        from struct import unpack_from
+
+        data = open(filename, 'rb').read()
+
+        fmt = "BBBBIIIIIII"
+        values = unpack_from(fmt, data)
+
+        if values[:len(_MAGIC)] != _MAGIC:
+            raise Exception("Bad magic number in header")
+
+        header = PSF2.Header(*values[len(_MAGIC):])
+        if header.version != _VERSION:
+            raise Exception(f"Bad version {header.version} in header")
+
+        return cls(basename(filename), header, data)
+
+    class Glyph:
+        __slots__ = ['index', 'data']
+        def __init__(self, i, data):
+            self.index = i
+            self.data = data
+        def __index__(self):
+            return self.index
+        def empty(self):
+            return not bool([b for b in self.data if b != 0])
+        def description(self):
+            c = chr(self.index)
+            if c.isprintable():
+                return "Glyph {:02x}: '{}'".format(self.index, c)
+            else:
+                return "Glyph {:02x}".format(self.index)
+
+    def __getitem__(self, i):
+        c = self.__header.charsize
+        n = i * c + self.__header.offset
+        return PSF2.Glyph(i, self.__data[n:n+c])
+
+    class __iter:
+        __slots__ = ['font', 'n']
+        def __init__(self, font):
+            self.font = font
+            self.n = 0
+        def __next__(self):
+            if self.n < self.font.count:
+                glyph = self.font[self.n]
+                self.n += 1
+                return glyph
+            else:
+                raise StopIteration
+
+    def __iter__(self):
+        return PSF2.__iter(self)

scripts/parse_font.py

@@ -1,21 +1,6 @@
 #!/usr/bin/env python3
 
-MAGIC = (0x72, 0xb5, 0x4a, 0x86)
-
-from collections import namedtuple
-PSF2 = namedtuple("PSF2", ["version", "offset", "flags", "count", "charsize", "height", "width"])
-
-def read_header(data):
-    from struct import unpack_from, calcsize
-
-    fmt = "BBBBIIIIIII"
-
-    values = unpack_from(fmt, data)
-    if values[:len(MAGIC)] != MAGIC:
-        raise Exception("Bad magic number in header")
-
-    return PSF2(*values[len(MAGIC):])
-
+from fontpsf import PSF2
 
 def print_glyph(header, data):
     bw = (header.width + 7) // 8
@@ -28,16 +13,15 @@ def print_glyph(header, data):
 
 
 def display_font(filename):
-    data = open(filename, 'rb').read()
+    font = PSF2.load(filename)
+    print(font.header)
 
-    header = read_header(data)
-    print(header)
-
-    c = header.charsize
-    for i in range(0, header.count):
-        n = i * c + header.offset
-        print("Glyph {}:".format(i))
-        print_glyph(header, data[n:n+c])
+    for glyph in font:
+        if glyph.empty():
+            print("{}: BLANK".format(glyph.description()))
+        else:
+            print("{}:".format(glyph.description()))
+            print_glyph(font.header, glyph.data)
 
 
 if __name__ == "__main__":

scripts/psf_to_cpp.py

@@ -0,0 +1,27 @@
+#!/usr/bin/env python3
+
+from fontpsf import PSF2
+
+def print_header(filename):
+    font = PSF2.load(filename)
+
+    print("#pragma once")
+    print(f"// This file was autogenerated by psf_to_cpp.py from {font.filename}\n")
+
+    print(f"const uint8_t font_glyph_size = {font.charsize};")
+    print(f"const uint8_t font_glyph_width = {font.dimension[0]};")
+    print(f"const uint8_t font_glyph_height = {font.dimension[1]};")
+    print(f"const uint16_t font_glyph_count = {font.count};\n")
+
+    print('const uint8_t font_glyph_data[] = {')
+
+    for glyph in font:
+        print("    ", "".join([f"0x{b:02x}," for b in glyph.data]), end="")
+        print(" // {}".format(glyph.description()))
+
+    print("};")
+
+if __name__ == "__main__":
+    import sys
+    for filename in sys.argv[1:]:
+        print_header(filename)