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font: shape combining marks with harfbuzz instead of stacking

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Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I64d67dbc96ce3faa68d221252e44d9976a6a6964
This commit is contained in:
raf 2026-06-26 10:42:50 +03:00
commit 5d132d9ac7
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GPG key ID: 29D95B64378DB4BF
5 changed files with 317 additions and 72 deletions
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118
src/render.rs
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@ -7,7 +7,7 @@
use std::num::NonZeroU16;
use crate::font::{CellMetrics, Fonts, GlyphData, Style};
use crate::font::{CellMetrics, Fonts, Glyph, GlyphData, Style};
use crate::grid::{Cell, CursorShape, Flags, Grid, Underline};
use crate::theme::{Plane, Rgb, Theme};
@ -205,19 +205,47 @@ impl Renderer {
}
let (fg, _) = cell_colors(cell, theme);
let origin_x = pad_x + x as i32 * m.width as i32;
if is_braille(cell.c) {
let style = cell_style(cell);
// A cell carrying combining marks is shaped as a cluster so the
// marks land where the font's GPOS table wants them. Shaping returns
// None for braille (drawn directly) and for clusters the face does
// not fully cover, both of which fall through to the legacy path.
let shaped = match &cell.combining {
Some(marks) if !is_braille(cell.c) => {
self.fonts.shape_cluster(cell.c, marks, style)
}
_ => None,
};
if let Some(shaped) = shaped {
for placed in &shaped.glyphs {
if let Ok(glyph) = self.fonts.glyph_indexed(shaped.face_idx, placed.gid, style)
{
blit_glyph(
&mut canvas,
glyph,
m,
origin_x + placed.x,
row_top,
placed.y,
fg,
);
}
}
} else if is_braille(cell.c) {
// Drawn directly so the dots are crisp and fill the cell, the
// way tools like btop expect, rather than however the fallback
// font happens to size its braille glyphs.
draw_braille(&mut canvas, cell.c, origin_x, row_top, m, fg);
} else if cell.c != ' ' {
self.draw_glyph(&mut canvas, cell.c, cell_style(cell), origin_x, row_top, fg);
}
// Stack any combining marks over the base glyph; their own bearings
// position them (no shaper, so placement is the font's default).
if let Some(marks) = &cell.combining {
for mark in marks.chars() {
self.draw_glyph(&mut canvas, mark, cell_style(cell), origin_x, row_top, fg);
} else {
if cell.c != ' ' {
self.draw_glyph(&mut canvas, cell.c, style, origin_x, row_top, fg);
}
// No shaper available for this cluster: stack the marks over the
// base using each mark glyph's own bearings.
if let Some(marks) = &cell.combining {
for mark in marks.chars() {
self.draw_glyph(&mut canvas, mark, style, origin_x, row_top, fg);
}
}
}
draw_decorations(&mut canvas, cell, theme, origin_x, row_top, m, fg);
@ -414,40 +442,50 @@ impl Renderer {
return;
}
};
let (gw, gh) = (glyph.width as i32, glyph.height as i32);
match &glyph.data {
GlyphData::Mask(mask) => {
let baseline = cell_top + m.ascent as i32;
for gy in 0..gh {
for gx in 0..gw {
let a = mask[(gy * gw + gx) as usize];
if a != 0 {
canvas.blend(
origin_x + glyph.left + gx,
baseline - glyph.top + gy,
fg,
a,
);
}
blit_glyph(canvas, glyph, m, origin_x, cell_top, 0, fg);
}
}
/// Composite a rasterized glyph into the canvas. `origin_x`/`cell_top` are the
/// cell's top-left; `rise` lifts the glyph above the baseline (HarfBuzz's
/// vertical offset, 0 for the unshaped path).
fn blit_glyph(
canvas: &mut Canvas,
glyph: &Glyph,
m: CellMetrics,
origin_x: i32,
cell_top: i32,
rise: i32,
fg: Rgb,
) {
let (gw, gh) = (glyph.width as i32, glyph.height as i32);
match &glyph.data {
GlyphData::Mask(mask) => {
let baseline = cell_top + m.ascent as i32 - rise;
for gy in 0..gh {
for gx in 0..gw {
let a = mask[(gy * gw + gx) as usize];
if a != 0 {
canvas.blend(origin_x + glyph.left + gx, baseline - glyph.top + gy, fg, a);
}
}
}
// Colour glyphs (emoji) come from a fixed strike at native size;
// scale them to the line height with nearest-neighbour sampling.
GlyphData::Color(bgra) if gh > 0 => {
let scale = m.height as f32 / gh as f32;
let target_w = (gw as f32 * scale) as i32;
for ty in 0..m.height as i32 {
let sy = ((ty as f32 / scale) as i32).min(gh - 1);
for tx in 0..target_w {
let sx = ((tx as f32 / scale) as i32).min(gw - 1);
let i = ((sy * gw + sx) * 4) as usize;
canvas.over(origin_x + tx, cell_top + ty, &bgra[i..i + 4]);
}
}
}
GlyphData::Color(_) => {}
}
// Colour glyphs (emoji) come from a fixed strike at native size;
// scale them to the line height with nearest-neighbour sampling.
GlyphData::Color(bgra) if gh > 0 => {
let scale = m.height as f32 / gh as f32;
let target_w = (gw as f32 * scale) as i32;
for ty in 0..m.height as i32 {
let sy = ((ty as f32 / scale) as i32).min(gh - 1);
for tx in 0..target_w {
let sx = ((tx as f32 / scale) as i32).min(gw - 1);
let i = ((sy * gw + sx) * 4) as usize;
canvas.over(origin_x + tx, cell_top + ty, &bgra[i..i + 4]);
}
}
}
GlyphData::Color(_) => {}
}
}