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Improve text layout heuristics and use layout log attributes

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This change gives amazing speeding results with long texts.
This commit is contained in:
Guillaume Ayoub
2025-01-24 23:23:44 +01:00
parent 7fac29b9b8
commit 1f76d025e4
2 changed files with 57 additions and 35 deletions
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weasyprint/text/ffi.py
+2
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@@ -272,6 +272,8 @@ ffi.cdef('''
void pango_layout_line_get_extents (
PangoLayoutLine *line, PangoRectangle *ink_rect, PangoRectangle *logical_rect);
PangoLayoutLine * pango_layout_get_line_readonly (PangoLayout *layout, int line);
const PangoLogAttr* pango_layout_get_log_attrs_readonly (
PangoLayout* layout, gint* n_attrs);
hb_font_t * pango_font_get_hb_font (PangoFont *font);
weasyprint/text/line_break.py
+55 -35
View File
@@ -270,81 +270,101 @@ def split_first_line(text, style, context, max_width, justification_spacing,
if not text_wrap:
max_width = None
# Step #1: Get a draft layout with the first line
# Step #1: Get a draft layout with the first line.
ratio = 4 # number that almost always respects char_height / char_width > ratio
short_text = text
if max_width is not None and max_width != inf and style['font_size']:
short_text = text
if max_width == 0:
# Trying to find minimum size, let's naively split on spaces and
# keep one word + one letter
# Try to use a small amount of text to avoid the whole layout. We need
# at least one line, and one possible line break point on the second line.
if style['font_size'] * ratio > max_width:
# Trying to find minimum or very small size, let's naively split on
# spaces and keep one word + one letter.
space_index = text.find(' ')
if space_index != -1:
short_text = text[:space_index+2] # index + space + one letter
else:
short_text = text[:int(max_width / style['font_size'] * 2.5)]
# Try to use a small amount of text instead of the whole text
# Use the magic ration and hope that we’ll get the right amount of text.
short_text = text[:int(max_width / style['font_size'] * ratio)]
layout = create_layout(
short_text, style, context, max_width, justification_spacing)
first_line, resume_index = layout.get_first_line()
if resume_index is None and short_text != text:
# The small amount of text fits in one line, give up and use
# the whole text
# The small amount of text fits in one line, give up and use the
# whole text.
short_text = text
layout.set_text(text)
first_line, resume_index = layout.get_first_line()
else:
# If the second line of the short text can break, we have the next
# line break point required for step #3 in it, drop the end of the text.
first_line_text = short_text.encode()[:resume_index].decode()
if first_line_text != short_text:
start, end = len(first_line_text) + 1, len(short_text)
text_end_log_attrs = pango.pango_layout_get_log_attrs_readonly(
layout.layout, ffi.NULL)[start:end]
if get_next_break_point(text_end_log_attrs) is not None:
text = short_text
else:
layout = create_layout(
text, style, context, original_max_width, justification_spacing)
first_line, resume_index = layout.get_first_line()
# Step #2: Don't split lines when it's not needed
# Step #2: Don't split lines when it's not needed.
if max_width is None:
# The first line can take all the place needed
# The first line can take all the place needed.
return first_line_metrics(
first_line, text, layout, resume_index, space_collapse, style)
first_line_width, _ = line_size(first_line, style)
if resume_index is None and first_line_width <= max_width:
# The first line fits in the available width
# The first line fits in the available width.
return first_line_metrics(
first_line, text, layout, resume_index, space_collapse, style)
# Step #3: Try to put the first word of the second line on the first line
# https://mail.gnome.org/archives/gtk-i18n-list/2013-September/msg00006
# is a good thread related to this problem.
first_line_text = text.encode()[:resume_index].decode()
first_line_fits = (
first_line_width <= max_width or
can_break_text(first_line_text.strip(), style['lang']))
if first_line_fits:
# The first line fits but may have been cut too early by Pango
second_line_text = text.encode()[resume_index:].decode()
if first_line_width <= max_width:
# The first line fits but may have been cut too early by Pango.
encoded_text = text.encode()
first_line_text = encoded_text[:resume_index].decode()
second_line_text = encoded_text[resume_index:].decode()
else:
# The line can't be split earlier, try to hyphenate the first word.
first_line_text = ''
second_line_text = text
break_point = next_break_point(second_line_text, style['lang'])
if first_line_text == short_text:
# There’s no second line, don’t try to find a next word.
break_point = None
else:
# Find then second line’s first break point.
log_attrs = pango.pango_layout_get_log_attrs_readonly(layout.layout, ffi.NULL)
start, end = len(first_line_text) + 1, len(short_text)
second_line_log_attrs = log_attrs[start:end]
break_point = get_next_break_point(second_line_log_attrs)
if break_point is not None:
break_point -= len(first_line_text) + 1
next_word = second_line_text[:break_point].rstrip(' ')
if next_word:
if space_collapse and second_line_text[break_point or -1] == ' ':
# next_word might fit without a space afterwards
# only try when space collapsing is allowed
# Next word might fit without a space afterwards only try when
# space collapsing is allowed.
new_first_line_text = first_line_text + next_word
layout.set_text(new_first_line_text)
first_line, resume_index = layout.get_first_line()
if resume_index is None:
if first_line_text:
# The next word fits in the first line, keep the layout
# The next word fits in the first line, keep the layout.
resume_index = len(new_first_line_text.encode()) + 1
return first_line_metrics(
first_line, text, layout, resume_index, space_collapse,
style)
first_line, text, layout, resume_index, space_collapse, style)
else:
# Second line is None
# Second line is None.
resume_index = first_line.length + 1
if resume_index >= len(text.encode()):
resume_index = None
elif first_line_text:
# We found something on the first line but we did not find a word on
# the next line, no need to hyphenate, we can keep the current layout
# the next line, no need to hyphenate, we can keep the current layout.
return first_line_metrics(
first_line, text, layout, resume_index, space_collapse, style)
@@ -499,18 +519,18 @@ def get_log_attrs(text, lang):
return log_attrs
def next_break_point(text, lang):
if not text or len(text) < 2:
return None
log_attrs = get_log_attrs(text, lang)
length = len(text) + 1
for i, attr in enumerate(log_attrs[1:length - 1]):
def get_next_break_point(log_attrs):
for i, attr in enumerate(log_attrs):
if attr.is_line_break:
return i
def can_break_text(text, lang):
return next_break_point(text, lang) is not None
if not text or len(text) < 2:
return None
log_attrs = get_log_attrs(text, lang)
length = len(text) + 1
return get_next_break_point(log_attrs[1:length-1]) is not None
def get_next_word_boundaries(text, lang):