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Make text underline and strikethrough pixel perfect crisp (#5857)

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Small visual fix: pixel-align any text underline or strikethrough.
Before they could be often be blurry.
This commit is contained in:
Emil Ernerfeldt
2025-03-28 20:37:38 +01:00
committed by GitHub
parent 884be3491d
commit 7ea3f762b8
4 changed files with 67 additions and 56 deletions
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56
crates/epaint/src/tessellator.rs
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@@ -1656,7 +1656,7 @@ impl Tessellator {
if a.x == b.x {
// Vertical line
let mut x = a.x;
round_line_segment(&mut x, &stroke, self.pixels_per_point);
stroke.round_center_to_pixel(self.pixels_per_point, &mut x);
a.x = x;
b.x = x;
@@ -1677,7 +1677,7 @@ impl Tessellator {
if a.y == b.y {
// Horizontal line
let mut y = a.y;
round_line_segment(&mut y, &stroke, self.pixels_per_point);
stroke.round_center_to_pixel(self.pixels_per_point, &mut y);
a.y = y;
b.y = y;
@@ -1778,7 +1778,6 @@ impl Tessellator {
let mut corner_radius = CornerRadiusF32::from(corner_radius);
let round_to_pixels = round_to_pixels.unwrap_or(self.options.round_rects_to_pixels);
let pixel_size = 1.0 / self.pixels_per_point;
if stroke.width == 0.0 {
stroke.color = Color32::TRANSPARENT;
@@ -1849,17 +1848,7 @@ impl Tessellator {
}
StrokeKind::Middle => {
// On this path we optimize for crisp and symmetric strokes.
// We put odd-width strokes in the center of pixels.
// To understand why, see `fn round_line_segment`.
if stroke.width <= 0.0 {
rect = rect.round_to_pixels(self.pixels_per_point);
} else if stroke.width <= pixel_size
|| is_nearest_integer_odd(self.pixels_per_point * stroke.width)
{
rect = rect.round_to_pixel_center(self.pixels_per_point);
} else {
rect = rect.round_to_pixels(self.pixels_per_point);
}
stroke.round_rect_to_pixel(self.pixels_per_point, &mut rect);
}
StrokeKind::Outside => {
// Put the inside of the stroke on a pixel boundary.
@@ -2203,45 +2192,6 @@ impl Tessellator {
}
}
fn round_line_segment(coord: &mut f32, stroke: &Stroke, pixels_per_point: f32) {
// If the stroke is an odd number of pixels wide,
// we want to round the center of it to the center of a pixel.
//
// If however it is an even number of pixels wide,
// we want to round the center to be between two pixels.
//
// We also want to treat strokes that are _almost_ odd as it it was odd,
// to make it symmetric. Same for strokes that are _almost_ even.
//
// For strokes less than a pixel wide we also round to the center,
// because it will rendered as a single row of pixels by the tessellator.
let pixel_size = 1.0 / pixels_per_point;
if stroke.width <= pixel_size || is_nearest_integer_odd(pixels_per_point * stroke.width) {
*coord = coord.round_to_pixel_center(pixels_per_point);
} else {
*coord = coord.round_to_pixels(pixels_per_point);
}
}
fn is_nearest_integer_odd(width: f32) -> bool {
(width * 0.5 + 0.25).fract() > 0.5
}
#[test]
fn test_is_nearest_integer_odd() {
assert!(is_nearest_integer_odd(0.6));
assert!(is_nearest_integer_odd(1.0));
assert!(is_nearest_integer_odd(1.4));
assert!(!is_nearest_integer_odd(1.6));
assert!(!is_nearest_integer_odd(2.0));
assert!(!is_nearest_integer_odd(2.4));
assert!(is_nearest_integer_odd(2.6));
assert!(is_nearest_integer_odd(3.0));
assert!(is_nearest_integer_odd(3.4));
}
#[deprecated = "Use `Tessellator::new(…).tessellate_shapes(…)` instead"]
pub fn tessellate_shapes(
pixels_per_point: f32,