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Refactor: create Stroke::round_center_to_pixel

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This commit is contained in:
Emil Ernerfeldt
2025-03-28 20:22:10 +01:00
parent 25f647322e
commit ed847f1a55
2 changed files with 63 additions and 53 deletions
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60
crates/epaint/src/stroke.rs
View File

@@ -2,6 +2,8 @@
use std::{fmt::Debug, sync::Arc};
use emath::GuiRounding as _;
use super::{emath, Color32, ColorMode, Pos2, Rect};
/// Describes the width and color of a line.
@@ -34,6 +36,46 @@ impl Stroke {
pub fn is_empty(&self) -> bool {
self.width <= 0.0 || self.color == Color32::TRANSPARENT
}
/// For vertical or horizontal lines:
/// round the stroke center to produce a sharp, pixel-aligned line.
pub fn round_center_to_pixel(&self, pixels_per_point: f32, coord: &mut 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 self.width <= pixel_size || is_nearest_integer_odd(pixels_per_point * self.width) {
*coord = coord.round_to_pixel_center(pixels_per_point);
} else {
*coord = coord.round_to_pixels(pixels_per_point);
}
}
pub(crate) fn round_rect_to_pixel(&self, pixels_per_point: f32, rect: &mut Rect) {
// We put odd-width strokes in the center of pixels.
// To understand why, see `fn round_center_to_pixel`.
let pixel_size = 1.0 / pixels_per_point;
let width = self.width;
if width <= 0.0 {
*rect = rect.round_to_pixels(pixels_per_point);
} else if width <= pixel_size || is_nearest_integer_odd(pixels_per_point * width) {
*rect = rect.round_to_pixel_center(pixels_per_point);
} else {
*rect = rect.round_to_pixels(pixels_per_point);
}
}
}
impl<Color> From<(f32, Color)> for Stroke
@@ -182,3 +224,21 @@ impl From<Stroke> for PathStroke {
}
}
}
/// Returns true if the nearest integer is odd.
fn is_nearest_integer_odd(x: f32) -> bool {
(x * 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));
}

56
crates/epaint/src/tessellator.rs
View File

@@ -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_coord_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_coord_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.
@@ -2205,45 +2194,6 @@ 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,