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Even better

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Emil Ernerfeldt
2025-02-04 15:19:56 +01:00
parent e97d1c7718
commit db29cc5ca1
1 changed files with 13 additions and 9 deletions
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22
crates/epaint/src/tessellator.rs
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@@ -1646,6 +1646,8 @@ impl Tessellator {
let feathering = self.feathering; let feathering = self.feathering;
let pixels_per_point = self.pixels_per_point; let pixels_per_point = self.pixels_per_point;
let quarter_pixel = 0.25 * feathering; // Used to avoid fence post problem.
let [a, b] = &mut points; let [a, b] = &mut points;
if a.x == b.x { if a.x == b.x {
// Vertical line // Vertical line
@@ -1656,14 +1658,16 @@ impl Tessellator {
// Often the ends of the line are exactly on a pixel boundary, // 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… // 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), // Solution: first shrink the line segment (on each end),
// then round to pixel center! // then round to pixel center!
// We shrink by half-a-pixel n total (a quarter on each end),
// so that on average we avoid the fence-post-problem after rounding.
if a.y < b.y { if a.y < b.y {
a.y = (a.y + 0.5 * feathering).round_to_pixel_center(pixels_per_point); a.y = (a.y + quarter_pixel).round_to_pixel_center(pixels_per_point);
b.y = (b.y - 0.5 * feathering).round_to_pixel_center(pixels_per_point); b.y = (b.y - quarter_pixel).round_to_pixel_center(pixels_per_point);
} else { } else {
a.y = (a.y - 0.5 * feathering).round_to_pixel_center(pixels_per_point); a.y = (a.y - quarter_pixel).round_to_pixel_center(pixels_per_point);
b.y = (b.y + 0.5 * feathering).round_to_pixel_center(pixels_per_point); b.y = (b.y + quarter_pixel).round_to_pixel_center(pixels_per_point);
} }
} }
if a.y == b.y { if a.y == b.y {
@@ -1675,11 +1679,11 @@ impl Tessellator {
// See earlier comment for vertical lines // See earlier comment for vertical lines
if a.x < b.x { if a.x < b.x {
a.x = (a.x + 0.5 * feathering).round_to_pixel_center(pixels_per_point); a.x = (a.x + quarter_pixel).round_to_pixel_center(pixels_per_point);
b.x = (b.x - 0.5 * feathering).round_to_pixel_center(pixels_per_point); b.x = (b.x - quarter_pixel).round_to_pixel_center(pixels_per_point);
} else { } else {
a.x = (a.x - 0.5 * feathering).round_to_pixel_center(pixels_per_point); a.x = (a.x - quarter_pixel).round_to_pixel_center(pixels_per_point);
b.x = (b.x + 0.5 * feathering).round_to_pixel_center(pixels_per_point); b.x = (b.x + quarter_pixel).round_to_pixel_center(pixels_per_point);
} }
} }
} }