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@@ -1646,6 +1646,8 @@ impl Tessellator {
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let feathering = self.feathering;
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let pixels_per_point = self.pixels_per_point;
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let quarter_pixel = 0.25 * feathering; // Used to avoid fence post problem.
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let [a, b] = &mut points;
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if a.x == b.x {
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// Vertical line
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@@ -1656,14 +1658,16 @@ impl Tessellator {
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// Often the ends of the line are exactly on a pixel boundary,
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// but we extend line segments with a cap that is a pixel wide…
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// Solution: first shrink the pixel by half a pixel (on each end),
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// Solution: first shrink the line segment (on each end),
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// then round to pixel center!
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// We shrink by half-a-pixel n total (a quarter on each end),
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// so that on average we avoid the fence-post-problem after rounding.
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if a.y < b.y {
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a.y = (a.y + 0.5 * feathering).round_to_pixel_center(pixels_per_point);
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b.y = (b.y - 0.5 * feathering).round_to_pixel_center(pixels_per_point);
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a.y = (a.y + quarter_pixel).round_to_pixel_center(pixels_per_point);
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b.y = (b.y - quarter_pixel).round_to_pixel_center(pixels_per_point);
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} else {
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a.y = (a.y - 0.5 * feathering).round_to_pixel_center(pixels_per_point);
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b.y = (b.y + 0.5 * feathering).round_to_pixel_center(pixels_per_point);
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a.y = (a.y - quarter_pixel).round_to_pixel_center(pixels_per_point);
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b.y = (b.y + quarter_pixel).round_to_pixel_center(pixels_per_point);
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}
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}
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if a.y == b.y {
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@@ -1675,11 +1679,11 @@ impl Tessellator {
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// See earlier comment for vertical lines
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if a.x < b.x {
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a.x = (a.x + 0.5 * feathering).round_to_pixel_center(pixels_per_point);
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b.x = (b.x - 0.5 * feathering).round_to_pixel_center(pixels_per_point);
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a.x = (a.x + quarter_pixel).round_to_pixel_center(pixels_per_point);
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b.x = (b.x - quarter_pixel).round_to_pixel_center(pixels_per_point);
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} else {
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a.x = (a.x - 0.5 * feathering).round_to_pixel_center(pixels_per_point);
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b.x = (b.x + 0.5 * feathering).round_to_pixel_center(pixels_per_point);
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a.x = (a.x - quarter_pixel).round_to_pixel_center(pixels_per_point);
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b.x = (b.x + quarter_pixel).round_to_pixel_center(pixels_per_point);
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}
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}
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}
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