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Fix offset by 1 when computing gradient fill color #130

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Merged
merged 2 commits into from
Oct 10, 2025
Merged

Fix offset by 1 when computing gradient fill color #130

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08c8051
fix gradient fill offset
Yohsi Aug 21, 2025
5e188b8
Merge branch 'main' into fix-gradient-fill-offset
emilk Oct 10, 2025
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28 changes: 18 additions & 10 deletions egui_plot/src/items/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -531,32 +531,39 @@ impl PlotItem for Line<'_> {
let y = transform
.position_from_point(&PlotPoint::new(0.0, y_reference))
.y;
let mut fill_color = Rgba::from(stroke.color)
let default_fill_color = Rgba::from(stroke.color)
.to_opaque()
.multiply(fill_alpha)
.into();
let mut mesh = Mesh::default();
let expected_intersections = 20;
mesh.reserve_triangles((n_values - 1) * 2);
mesh.reserve_vertices(n_values * 2 + expected_intersections);
values_tf.windows(2).for_each(|w| {

let fill_color_for_point = |pos| {
if *gradient_fill && self.gradient_color.is_some() {
fill_color = Rgba::from(self
Rgba::from(self
.gradient_color
.clone()
.expect("Could not find gradient color callback")(
transform.value_from_position(w[1]),
transform.value_from_position(pos),
))
.to_opaque()
.multiply(fill_alpha)
.into();
.into()
} else {
default_fill_color
}
};

let mut mesh = Mesh::default();
let expected_intersections = 20;
mesh.reserve_triangles((n_values - 1) * 2);
mesh.reserve_vertices(n_values * 2 + expected_intersections);
values_tf.windows(2).for_each(|w| {
let fill_color = fill_color_for_point(w[0]);
let i = mesh.vertices.len() as u32;
mesh.colored_vertex(w[0], fill_color);
mesh.colored_vertex(pos2(w[0].x, y), fill_color);
if let Some(x) = y_intersection(&w[0], &w[1], y) {
let point = pos2(x, y);
mesh.colored_vertex(point, fill_color);
mesh.colored_vertex(point, fill_color_for_point(point));
mesh.add_triangle(i, i + 1, i + 2);
mesh.add_triangle(i + 2, i + 3, i + 4);
} else {
Expand All @@ -565,6 +572,7 @@ impl PlotItem for Line<'_> {
}
});
let last = values_tf[n_values - 1];
let fill_color = fill_color_for_point(last);
mesh.colored_vertex(last, fill_color);
mesh.colored_vertex(pos2(last.x, y), fill_color);
shapes.push(Shape::Mesh(std::sync::Arc::new(mesh)));
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