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Add Cluster::from_point_exact method for hit-testing spans #447

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Merged
nicoburns merged 1 commit into from
Oct 31, 2025
Merged

Add Cluster::from_point_exact method for hit-testing spans #447

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32 changes: 28 additions & 4 deletions parley/src/layout/cluster.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -53,8 +53,29 @@ impl<'a, B: Brush> Cluster<'a, B> {
None
}

/// Returns the cluster and side for the given layout and point.
/// Returns the cluster and side which is at the specified position in the given layout. If no cluster is
/// under the specified point then None will be returned.
///
/// This is usually the expected behaviour when hit-testing clusters for "hover" or "click" functionality.
pub fn from_point_exact(layout: &'a Layout<B>, x: f32, y: f32) -> Option<(Self, ClusterSide)> {
Cluster::from_point_impl(layout, x, y, true)
}

/// Returns the cluster and side which is at the specified position in the given layout. If no cluster is
/// under the specified point but the point is within the overall layout area then it will return the nearest.
///
/// This is usually the expected behaviour when hit-testing clusers for text selection or caret positioning.
pub fn from_point(layout: &'a Layout<B>, x: f32, y: f32) -> Option<(Self, ClusterSide)> {
Cluster::from_point_impl(layout, x, y, false)
}

/// Returns the cluster and side for the given layout and point.
fn from_point_impl(
layout: &'a Layout<B>,
x: f32,
y: f32,
exact: bool,
) -> Option<(Self, ClusterSide)> {
let mut path = ClusterPath::default();
if let Some((line_index, line)) = layout.line_for_offset(y) {
path.line_index = line_index as u32;
Expand All @@ -67,7 +88,7 @@ impl<'a, B: Brush> Cluster<'a, B> {
let run_advance = run.advance();
path.run_index = run.index;
path.logical_index = 0;
if x > offset + run_advance && !is_last_run {
if x > offset + run_advance && (exact || !is_last_run) {
offset += run_advance;
continue;
}
Expand All @@ -79,7 +100,10 @@ impl<'a, B: Brush> Cluster<'a, B> {
let cluster_advance = cluster.advance();
let edge = offset;
offset += cluster_advance;
if x > offset && !is_last_cluster {
if x > offset && (exact || !is_last_cluster) {
continue;
}
if x < edge && exact {
continue;
}
let side = if x <= edge + cluster_advance * 0.5 {
Expand All @@ -96,7 +120,7 @@ impl<'a, B: Brush> Cluster<'a, B> {
}
}
}
if y <= 0.0 {
if y <= 0.0 && !exact {
Some((path.cluster(layout)?, ClusterSide::Left))
} else {
None
Expand Down