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Better rounding of line segment end points

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This commit is contained in:
Emil Ernerfeldt
2025-02-04 15:17:28 +01:00
parent e4e0fc96b4
commit e97d1c7718
1 changed files with 22 additions and 4 deletions
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26
crates/epaint/src/tessellator.rs
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@@ -1643,6 +1643,9 @@ impl Tessellator {
}
if self.options.round_line_segments_to_pixels {
let feathering = self.feathering;
let pixels_per_point = self.pixels_per_point;
let [a, b] = &mut points;
if a.x == b.x {
// Vertical line
@@ -1651,8 +1654,17 @@ impl Tessellator {
a.x = x;
b.x = x;
a.y = a.y.round_to_pixel_center(self.pixels_per_point);
b.y = b.y.round_to_pixel_center(self.pixels_per_point);
// Often the ends of the line are exactly on a pixel boundary,
// but we extend line segments with a cap that is a pixel wide…
// Solution: first shrink the pixel by half a pixel (on each end),
// then round to pixel center!
if a.y < b.y {
a.y = (a.y + 0.5 * feathering).round_to_pixel_center(pixels_per_point);
b.y = (b.y - 0.5 * feathering).round_to_pixel_center(pixels_per_point);
} else {
a.y = (a.y - 0.5 * feathering).round_to_pixel_center(pixels_per_point);
b.y = (b.y + 0.5 * feathering).round_to_pixel_center(pixels_per_point);
}
}
if a.y == b.y {
// Horizontal line
@@ -1661,8 +1673,14 @@ impl Tessellator {
a.y = y;
b.y = y;
a.x = a.x.round_to_pixel_center(self.pixels_per_point);
b.x = b.x.round_to_pixel_center(self.pixels_per_point);
// See earlier comment for vertical lines
if a.x < b.x {
a.x = (a.x + 0.5 * feathering).round_to_pixel_center(pixels_per_point);
b.x = (b.x - 0.5 * feathering).round_to_pixel_center(pixels_per_point);
} else {
a.x = (a.x - 0.5 * feathering).round_to_pixel_center(pixels_per_point);
b.x = (b.x + 0.5 * feathering).round_to_pixel_center(pixels_per_point);
}
}
}