gregor/jprototerm
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

hoist row hash out of detectShift delta scan

Browse Source 
rowFingerprint(row) is invariant across the delta loop but was recomputed for
every candidate delta, making shift detection O(rows^2 x cols) on large changes
(full-screen scroll). Precompute each changed row's hash once, dropping it to
O(rows x cols). Profiling showed fingerprint hashing at ~74% of frame time under
heavy scroll, dominated by this loop.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Gregor Lohaus
2026-05-31 21:09:54 +02:00
parent 1f7394d75a
commit 4923ea5527
1 changed files with 15 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

21
src/main/java/com/gregor/jprototerm/TerminalPaneNode.java
View File

@@ -253,21 +253,29 @@ final class TerminalPaneNode extends Region {
} }
private ShiftPlan detectShift(RenderStateSnapshot snapshot, List<RenderRow> changedRows) { private ShiftPlan detectShift(RenderStateSnapshot snapshot, List<RenderRow> changedRows) {
int rowCount = snapshot.rows();
int changedCount = changedRows.size();
// The new-content hash of each changed row is invariant across the delta scan below,
// so compute it once here instead of re-hashing the whole row for every candidate delta.
long[] changedHashes = new long[changedCount];
for (int i = 0; i < changedCount; i++) {
changedHashes[i] = rowFingerprint(changedRows.get(i));
}
int bestDelta = 0; int bestDelta = 0;
int bestScore = 0; int bestScore = 0;
int rowCount = snapshot.rows();
for (int delta = -rowCount + 1; delta < rowCount; delta++) { for (int delta = -rowCount + 1; delta < rowCount; delta++) {
if (delta == 0) { if (delta == 0) {
continue; continue;
} }
int score = 0; int score = 0;
for (RenderRow row : changedRows) { for (int i = 0; i < changedCount; i++) {
int sourceRow = row.row() + delta; int sourceRow = changedRows.get(i).row() + delta;
if (sourceRow < 0 || sourceRow >= rowCount || !rows.containsKey(sourceRow)) { if (sourceRow < 0 || sourceRow >= rowCount || !rows.containsKey(sourceRow)) {
continue; continue;
} }
Long previous = rowFingerprints.get(sourceRow); Long previous = rowFingerprints.get(sourceRow);
if (previous != null && previous == rowFingerprint(row)) { if (previous != null && previous == changedHashes[i]) {
score++; score++;
} }
} }
@@ -284,13 +292,14 @@ final class TerminalPaneNode extends Region {
List<RowMove> moves = new ArrayList<>(bestScore); List<RowMove> moves = new ArrayList<>(bestScore);
Set<Integer> targetRows = new HashSet<>(); Set<Integer> targetRows = new HashSet<>();
for (RenderRow row : changedRows) { for (int i = 0; i < changedCount; i++) {
RenderRow row = changedRows.get(i);
int sourceRow = row.row() + bestDelta; int sourceRow = row.row() + bestDelta;
if (sourceRow < 0 || sourceRow >= rowCount || !rows.containsKey(sourceRow)) { if (sourceRow < 0 || sourceRow >= rowCount || !rows.containsKey(sourceRow)) {
continue; continue;
} }
Long previous = rowFingerprints.get(sourceRow); Long previous = rowFingerprints.get(sourceRow);
if (previous != null && previous == rowFingerprint(row)) { if (previous != null && previous == changedHashes[i]) {
moves.add(new RowMove(sourceRow, row.row())); moves.add(new RowMove(sourceRow, row.row()));
targetRows.add(row.row()); targetRows.add(row.row());
} }