python3.6环境下如何安装freetype库和基本使用方法

FreeType库是一个完全免费（开源）的、高质量的且可移植的字体引擎，它提供统一的接口来访问多种字体格式文件，包括TrueType, OpenType, Type1, CID, CFF, Windows FON/FNT, X11 PCF等。在做图像展示的时候，可以写入中文文字，效果还是很好。

在之前安装库时基本都是直接切换到python3.6环境下直接pip install XXX，在安装freetype直接pip install freetype不可以了，查了半天又是编译又是官网下载的，太麻烦，不推荐。

（1）正确的安装方法：
注意：一定要加上 -py

pip install freetype-py

（2）常用调用方法

已经封装好了一个文件，可直接保存后调用。

import freetype
import copy

class put_chinese_text(object):
  def __init__(self, ttf):
    self._face = freetype.Face(ttf)

  def draw_text(self, image, pos, text, text_size, text_color):
    '''
    draw chinese(or not) text with ttf
    :param image:   image(numpy.ndarray) to draw text
    :param pos:    where to draw text
    :param text:   the context, for chinese should be unicode type
    :param text_size: text size
    :param text_color:text color
    :return:     image
    '''
    self._face.set_char_size(text_size * 64)
    metrics = self._face.size
    ascender = metrics.ascender / 64.0

    # descender = metrics.descender/64.0
    # height = metrics.height/64.0
    # linegap = height - ascender + descender
    ypos = int(ascender)

    text = text
    img = self.draw_string(image, pos[0], pos[1] + ypos, text, text_color)
    return img

  def draw_string(self, img, x_pos, y_pos, text, color):
    '''
    draw string
    :param x_pos: text x-postion on img
    :param y_pos: text y-postion on img
    :param text: text (unicode)
    :param color: text color
    :return:   image
    '''
    prev_char = 0
    pen = freetype.Vector()
    pen.x = x_pos << 6 # div 64
    pen.y = y_pos << 6

    hscale = 1.0
    matrix = freetype.Matrix(int(hscale) * 0x10000, int(0.2 * 0x10000), \
                 int(0.0 * 0x10000), int(1.1 * 0x10000))
    cur_pen = freetype.Vector()
    pen_translate = freetype.Vector()

    image = copy.deepcopy(img)
    for cur_char in text:
      self._face.set_transform(matrix, pen_translate)

      self._face.load_char(cur_char)
      kerning = self._face.get_kerning(prev_char, cur_char)
      pen.x += kerning.x
      slot = self._face.glyph
      bitmap = slot.bitmap

      cur_pen.x = pen.x
      cur_pen.y = pen.y - slot.bitmap_top * 64
      self.draw_ft_bitmap(image, bitmap, cur_pen, color)

      pen.x += slot.advance.x
      prev_char = cur_char

    return image

  def draw_ft_bitmap(self, img, bitmap, pen, color):
    '''
    draw each char
    :param bitmap: bitmap
    :param pen:  pen
    :param color: pen color e.g.(0,0,255) - red
    :return:    image
    '''
    x_pos = pen.x >> 6
    y_pos = pen.y >> 6
    cols = bitmap.width
    rows = bitmap.rows

    glyph_pixels = bitmap.buffer

    for row in range(rows):
      for col in range(cols):
        if glyph_pixels[row * cols + col] != 0:
          try:
            img[y_pos + row][x_pos + col][0] = color[0]
            img[y_pos + row][x_pos + col][1] = color[1]
            img[y_pos + row][x_pos + col][2] = color[2]
          except:
            continue

if __name__ == '__main__':
  # just for test
  import cv2

  line = '毛不易'
  img = cv2.imread('./aa.jpg')

  color_ = (0, 255, 0) # Green
  pos = (3, 3)
  text_size = 24
  ft = put_chinese_text('yahei.ttf')
  image = ft.draw_text(img, pos, line, text_size, color_)

  cv2.imshow('ss', image)
  cv2.waitKey(0)