File size: 3,237 Bytes
df84e45 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 | """Text layout, written to match what a browser does with the editor's CSS.
The editor draws a text element as one box with `white-space: pre`,
`line-height: <font_size * line_height>px`, `letter-spacing` and `text-align`.
This module reproduces that box model for skia, so the server render and the
browser render put glyphs in the same place:
- Lines are the explicit `\\n` breaks. Nothing wraps.
- Every line box is `font_size * line_height` tall.
- The baseline sits where CSS puts it: half of the leading above the font's
ascent, i.e. `top + (L - (ascent + descent)) / 2 + ascent`.
- `letter-spacing` is added after every character, trailing one included, which
is Chromium's behaviour and why right-aligned spaced text keeps a gap.
"""
from __future__ import annotations
from dataclasses import dataclass
from .doc import Element
from .fonts import FontRegistry
@dataclass
class Piece:
text: str
color: str
bold: bool
italic: bool
width: float
@dataclass
class Line:
pieces: list[Piece]
width: float
x: float # offset inside the box, from alignment
top: float # offset of the line box inside the element
baseline: float # offset of the baseline inside the element
@dataclass
class TextLayout:
lines: list[Line]
width: float # widest line
height: float # line count * line box height
line_box: float
def _split_lines(el: Element) -> list[list[tuple[str, object]]]:
"""Runs cut at newline boundaries, one list of (text, run) per line."""
lines: list[list[tuple[str, object]]] = [[]]
for run in el.styled_runs():
text = run.text.upper() if el.uppercase else run.text
parts = text.split("\n")
for i, part in enumerate(parts):
if i > 0:
lines.append([])
if part:
lines[-1].append((part, run))
return lines
def layout(el: Element, fonts: FontRegistry) -> TextLayout:
size = el.font_size
line_box = size * el.line_height
ascent, descent = fonts.metrics(el.font_family or "", size, el.bold, el.italic)
half_leading = (line_box - (ascent + descent)) / 2
lines = []
for i, raw in enumerate(_split_lines(el)):
pieces = []
for text, run in raw:
w = fonts.advance(
text, el.font_family or "", size, run.bold, run.italic, el.letter_spacing
)
pieces.append(Piece(text, run.color, bool(run.bold), bool(run.italic), w))
width = sum(p.width for p in pieces)
if el.align == "center":
x = (el.width - width) / 2
elif el.align == "right":
x = el.width - width
else:
x = 0.0
top = i * line_box
lines.append(Line(pieces, width, x, top, top + half_leading + ascent))
widest = max((ln.width for ln in lines), default=0.0)
return TextLayout(lines, widest, max(1.0, len(lines) * line_box), line_box)
def fit_box(el: Element, fonts: FontRegistry) -> tuple[float, float]:
"""(width, height) the element should have after a text or style change."""
lay = layout(el, fonts)
width = max(1.0, round(lay.width + 1.0, 2)) if el.auto_width else el.width
return width, round(lay.height, 2)
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