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Fix galley width calculation being off due to subpixel binning (#7972)

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- fix for https://github.com/rerun-io/reality/pull/1075

The galleys row size was calculated by looking at the last glyphs pos_x,
which got changed to be rounded to integers when we added subpixel
binning. This introduced a subtle bug which caused the width of galleys
to be slightly off.
This PR fixes this by looking at the actual cursor position instead,
which is not rounded.

Also added a test to ensure this is correct. Previously, for the second
and last line, the `x` was too close to the `0`.

<img width="48" height="67" alt="image"
src="https://github.com/user-attachments/assets/a69a4cc3-b3f3-4553-ab92-73cb2e7a358c"
/>

---------

Co-authored-by: lucasmerlin <8009393+lucasmerlin@users.noreply.github.com>
This commit is contained in:
Lucas Meurer
2026-03-12 13:49:16 +01:00
committed by GitHub
parent 8b90dc60c6
commit 14afefa252
118 changed files with 258 additions and 229 deletions
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23
crates/epaint/src/text/text_layout.rs
View File

@@ -114,7 +114,7 @@ pub fn layout(fonts: &mut FontsImpl, pixels_per_point: f32, job: Arc<LayoutJob>)
let intrinsic_size = calculate_intrinsic_size(point_scale, &job, &paragraphs);
let mut elided = false;
let mut rows = rows_from_paragraphs(paragraphs, &job, &mut elided);
let mut rows = rows_from_paragraphs(paragraphs, &job, pixels_per_point, &mut elided);
if elided && let Some(last_placed) = rows.last_mut() {
let last_row = Arc::make_mut(&mut last_placed.row);
replace_last_glyph_with_overflow_character(fonts, pixels_per_point, &job, last_row);
@@ -254,11 +254,12 @@ fn calculate_intrinsic_size(
) -> Vec2 {
let mut intrinsic_size = Vec2::ZERO;
for (idx, paragraph) in paragraphs.iter().enumerate() {
let width = paragraph
.glyphs
.last()
.map(|l| l.max_x())
.unwrap_or_default();
// Use the precise cursor position instead of `last_glyph.max_x()`,
// because glyph positions are pixel-snapped but the cursor tracks
// the exact subpixel advance. This ensures that when two galleys are
// placed side-by-side, the gap matches what it would be within a
// single galley.
let width = paragraph.cursor_x_px / point_scale.pixels_per_point;
intrinsic_size.x = f32::max(intrinsic_size.x, width);
let mut height = paragraph
@@ -279,6 +280,7 @@ fn calculate_intrinsic_size(
fn rows_from_paragraphs(
paragraphs: Vec<Paragraph>,
job: &LayoutJob,
pixels_per_point: f32,
elided: &mut bool,
) -> Vec<PlacedRow> {
let num_paragraphs = paragraphs.len();
@@ -305,8 +307,11 @@ fn rows_from_paragraphs(
ends_with_newline: !is_last_paragraph,
});
} else {
let paragraph_max_x = paragraph.glyphs.last().unwrap().max_x();
if paragraph_max_x <= job.effective_wrap_width() {
// Use precise cursor position for width instead of pixel-snapped
// `last_glyph.max_x()`, so that side-by-side galleys have the same
// spacing as characters within a single galley.
let paragraph_width = paragraph.cursor_x_px / pixels_per_point;
if paragraph_width <= job.effective_wrap_width() {
// Early-out optimization: the whole paragraph fits on one row.
rows.push(PlacedRow {
pos: pos2(0.0, f32::NAN),
@@ -314,7 +319,7 @@ fn rows_from_paragraphs(
section_index_at_start: paragraph.section_index_at_start,
glyphs: paragraph.glyphs,
visuals: Default::default(),
size: vec2(paragraph_max_x, 0.0),
size: vec2(paragraph_width, 0.0),
}),
ends_with_newline: !is_last_paragraph,
});