micropython-font-to-py/font_to_py/glyph.py

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4.9 KiB
Python
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# Some code adapted from Daniel Bader's work at the following URL
# https://dbader.org/blog/monochrome-font-rendering-with-freetype-and-python
# With thanks to Stephen Irons @ironss for various improvements, also to
# @enigmaniac for ideas around handling `bdf` and `pcf` files.
# The MIT License (MIT)
#
# Copyright (c) 2016-2023 Peter Hinch
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
from .bitmap import Bitmap
class Glyph:
def __init__( # noqa: PLR0913
self, pixels, width, height, top, left, advance_width
):
self.bitmap = Bitmap(width, height, pixels)
# The glyph bitmap's top-side bearing, i.e. the vertical distance from
# the baseline to the bitmap's top-most scanline.
self.top = top
self.left = left
# Ascent and descent determine how many pixels the glyph extends
# above or below the baseline.
self.descent = max(0, self.height - self.top)
self.ascent = max(0, max(self.top, self.height) - self.descent)
# The advance width determines where to place the next character
# horizontally, that is, how many pixels we move to the right to
# draw the next glyph.
self.advance_width = advance_width
@property
def width(self):
return self.bitmap.width
@property
def height(self):
return self.bitmap.height
@staticmethod
def from_glyphslot(slot):
"""Construct and return a Glyph object from a FreeType GlyphSlot."""
pixels = Glyph.unpack_mono_bitmap(slot.bitmap)
width, height = slot.bitmap.width, slot.bitmap.rows
top = slot.bitmap_top
left = slot.bitmap_left
# The advance width is given in FreeType's 26.6 fixed point format,
# which means that the pixel values are multiples of 64.
advance_width = slot.advance.x / 64
return Glyph(pixels, width, height, top, left, advance_width)
@staticmethod
def unpack_mono_bitmap(bitmap):
"""
Unpack a freetype FT_LOAD_TARGET_MONO glyph bitmap into a bytearray
where each pixel is represented by a single byte.
"""
# Allocate a bytearray of sufficient size to hold the glyph bitmap.
data = bytearray(bitmap.rows * bitmap.width)
# Iterate over every byte in the glyph bitmap. Note that we're not
# iterating over every pixel in the resulting unpacked bitmap --
# we're iterating over the packed bytes in the input bitmap.
for row in range(bitmap.rows):
for byte_index in range(bitmap.pitch):
# Read the byte that contains the packed pixel data.
byte_value = bitmap.buffer[row * bitmap.pitch + byte_index]
# We've processed this many bits (=pixels) so far. This
# determines where we'll read the next batch of pixels from.
num_bits_done = byte_index * 8
# Pre-compute where to write the pixels that we're going
# to unpack from the current byte in the glyph bitmap.
rowstart = row * bitmap.width + byte_index * 8
# Iterate over every bit (=pixel) that's still a part of the
# output bitmap. Sometimes we're only unpacking a fraction of
# a byte because glyphs may not always fit on a byte boundary.
# So we make sure to stop if we unpack past the current row
# of pixels.
for bit_index in range(min(8, bitmap.width - num_bits_done)):
# Unpack the next pixel from the current glyph byte.
bit = byte_value & (1 << (7 - bit_index))
# Write the pixel to the output bytearray. We ensure that
# `off` pixels have a value of 0 and `on` pixels have a
# value of 1.
data[rowstart + bit_index] = 1 if bit else 0
return data