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Avoid merging into empty layers in layer::Stack

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Héctor Ramón Jiménez 2025-08-19 08:06:25 +02:00
parent 806500048d
commit 9490d735c5
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1 changed files with 25 additions and 8 deletions
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33
graphics/src/layer.rs
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@ -143,39 +143,56 @@ impl<T: Layer> Stack<T> {
pub fn merge(&mut self) {
self.flush();
// These are the layers left to process
let mut left = self.active_count;
// There must be at least 2 or more layers to merge
while left > 1 {
// We set our target as the topmost layer left to process
let mut current = left - 1;
let mut last = &self.layers[current];
let mut last_start = last.start();
let mut target = &self.layers[current];
let mut target_start = target.start();
let mut target_index = current;
// We scan downwards for a contiguous block of mergeable layer candidates
while current > 0 {
let candidate = &self.layers[current - 1];
let start = candidate.start();
let end = candidate.end();
// We skip empty layers
if end == 0 {
current -= 1;
continue;
}
if end > last_start || candidate.bounds() != last.bounds() {
// Candidate can be merged if primitive sublayers do not overlap with
// previous targets and the clipping bounds match
if end > target_start || candidate.bounds() != target.bounds() {
break;
}
last = candidate;
last_start = start;
// Candidate is not empty and can be merged into
target = candidate;
target_start = start;
target_index = current;
current -= 1;
}
let (head, tail) = self.layers.split_at_mut(current + 1);
let layer = &mut head[current];
// We merge all the layers scanned into the target
//
// Since we use `target_index` instead of `current`, we
// deliberately avoid merging into empty layers.
//
// If no candidates were mergeable, this is a no-op.
let (head, tail) = self.layers.split_at_mut(target_index + 1);
let layer = &mut head[target_index];
for middle in &mut tail[0..left - current - 1] {
for middle in &mut tail[0..left - target_index - 1] {
layer.merge(middle);
}
// Empty layers found after the target can be skipped
left = current;
}
}