text_align_justify

#!/usr/bin/python3
#+
# Demonstration of basic (non-contextual, left-to-right) text layout,
# with horizontal alignment and justification.
#
# Copyright 2015 by Lawrence D'Oliveiro <ldo@geek-central.gen.nz>. This
# script is licensed CC0
# <https://creativecommons.org/publicdomain/zero/1.0/>; do with it
# what you will.
#-

import sys
import os
import qahirah as qah
from qahirah import \
    CAIRO, \
    Colour, \
    Glyph, \
    Rect, \
    Vector

def align_text(g, text_lines, line_width, align) :
    "renders the sequence of text_lines horizontally-aligned within line_width according" \
    " to align: 0 for left-aligned, 0.5 for centred, 1.0 for right-aligned; in-between" \
    " values also allowed. Returns the bounds of the rendered text."
    font_extents = g.font_extents
    bounds = Rect.empty
    for line in text_lines :
        save_pos = g.current_point
        extents = g.text_extents(line)
        if align != 0 :
            text_width = extents.width
            g.rel_move_to(((line_width - text_width) * align, 0))
        #end if
        bounds |= Rect(extents.x_bearing, extents.y_bearing, extents.width, extents.height) + g.current_point
        g.show_text(line)
        g.move_to(save_pos + Vector(0, font_extents.height))
    #end for
    return \
        bounds
#end align_text

def justify_text(g, text_lines, line_width, space_extra) :
    "renders the sequence of text_lines with full justification within line_width." \
    " space_extra is the relative amount of extra spacing to give to space glyphs; 0" \
    " means to treat them the same as non-space glyphs."
    space_glyph = g.scaled_font.text_to_glyphs((0, 0), " ", cluster_mapping = False)[0][0].index
    #sys.stderr.write("space_glyph = {}\n".format(space_glyph)) # debug
    font_extents = g.font_extents
    for line in text_lines :
        save_pos = g.current_point
        glyphs = g.scaled_font.text_to_glyphs(save_pos, line, cluster_mapping = False)[0]
        nr_spaces = len(tuple(g for g in glyphs if g.index == space_glyph))
        glyph_extents = g.glyph_extents(glyphs)
        glyph_adjust = \
            (
                (line_width - glyph_extents.width)
            /
                (len(glyphs) + nr_spaces * space_extra - 1)
            )
          # subtract 1 because no adjustment for first char on line, count of nr_spaces
          # assumes none are at beginning or end of line!
        new_glyphs = []
        prev_pos_x = 0
        prev_adj_pos_x = 0
        for i, glyph in enumerate(glyphs) :
            if i == 0 :
                adjust = 0
            elif glyph.index == space_glyph :
                adjust = glyph_adjust * (1 + space_extra)
            else :
                adjust = glyph_adjust
            #end if
            adj_pos_x = glyph.pos.x - prev_pos_x + prev_adj_pos_x + adjust
            new_glyphs.append \
              (
                Glyph(index = glyph.index, pos = (adj_pos_x, glyph.pos.y))
              )
            prev_pos_x = glyph.pos.x
            prev_adj_pos_x = adj_pos_x
        #end for
        g.show_glyphs(new_glyphs)
        g.move_to(save_pos + Vector(0, font_extents.height))
    #end for
#end justify_text

text_lines = \
    (
        "Lorem ipsum dolor sit amet, consectetur",
        "adipiscing elit, sed do eiusmod tempor",
        "incididunt ut labore et dolore magna aliqua.",
        "Ut enim ad minim veniam, quis nostrud",
        "exercitation ullamco laboris nisi ut aliquip",
        "ex ea commodo consequat. Duis aute irure dolor",
        "in reprehenderit in voluptate velit esse cillum",
        "dolore eu fugiat nulla pariatur. Excepteur sint",
        "occaecat cupidatat non proident, sunt in culpa",
        "qui officia deserunt mollit anim id est laborum.",
    )
text_size = 18
height_fudge = 1.4
line_width = text_size * 25
margin = 30

pix = qah.ImageSurface.create \
  (
    format = CAIRO.FORMAT_RGB24,
    dimensions = round(Vector
      (
        line_width * 2 + margin * 3,
        text_size * (len(text_lines) * 3 + 1) * height_fudge + margin * 4
      ))
  )
g = qah.Context.create(pix)
g.set_source_colour(Colour.grey(1)).set_operator(CAIRO.OPERATOR_SOURCE).paint()
g.set_source_colour(Colour.grey(0))
g.font_face = qah.FontFace.create_for_pattern("century schoolbook")
g.set_font_size(text_size)
font_extents = g.font_extents
g.move_to((margin, font_extents.ascent - font_extents.height + margin))
for align in (0, 0.5, 1.0) :
    g.rel_move_to((0, font_extents.height))
    bounds = align_text(g, text_lines, line_width, align)
    #sys.stderr.write("bounds = {}\n".format(bounds)) # debug
#end for
g.move_to((2 * margin + line_width, font_extents.ascent - font_extents.height + margin))
for space_extra in (0, 3, 10) :
    g.rel_move_to((0, font_extents.height))
    justify_text(g, text_lines, line_width, space_extra)
#end for

pix \
    .flush() \
    .write_to_png("%s.png" % os.path.basename(sys.argv[0]))