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StyledText: drawing with block selection can be very slow #3523 #3542

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StyledText: drawing with block selection can be very slow #3523 #3542

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1185b0d
StyledText: selecting larger number of rows gets very slow #3523
tmssngr Aug 27, 2026
3183837
StyledTextRenderer.intersectingRelativeNonEmptySelections: only creat…
tmssngr Aug 27, 2026
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22 changes: 11 additions & 11 deletions ...ipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/StyledTextRenderer.java
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Original file line number Diff line number Diff line change
Expand Up @@ -471,6 +471,7 @@ private LineDrawInfo makeLineDrawInfo(int lineIndex) {
}

int drawLines(int startLine, int endLine, int begX, int begY, int endY, GC gc, Color widgetBackground, Color widgetForeground) {
final int[] selectionRanges = styledText.getSelectionRanges();
// When fixed line metrics is in effect, tall unicode characters
// will not always fit line's height. In this case, they will
// draw out of line's bounds. To prevent them from being clipped
Expand Down Expand Up @@ -503,7 +504,7 @@ int drawLines(int startLine, int endLine, int begX, int begY, int endY, GC gc, C
// Draw foreground
y = begY;
for (LineDrawInfo lineInfo : drawInfos) {
drawLineForeground(lineInfo, begX, y, gc, widgetForeground);
drawLineForeground(lineInfo, begX, y, gc, widgetForeground, selectionRanges);
y += lineInfo.height;
}

Expand All @@ -519,7 +520,7 @@ int drawLines(int startLine, int endLine, int begX, int begY, int endY, GC gc, C
for (int iLine = startLine; y < endY && iLine < endLine; iLine++) {
LineDrawInfo lineInfo = makeLineDrawInfo(iLine);
drawLineBackground(lineInfo, y, gc, widgetBackground);
drawLineForeground(lineInfo, begX, y, gc, widgetForeground);
drawLineForeground(lineInfo, begX, y, gc, widgetForeground, selectionRanges);
disposeTextLayout(lineInfo.layout);
y += lineInfo.height;
}
Expand All @@ -546,10 +547,10 @@ private void drawLineBackground(LineDrawInfo lineInfo, int paintY, GC gc, Color
}
}

private void drawLineForeground(LineDrawInfo lineInfo, int paintX, int paintY, GC gc, Color widgetForeground) {
private void drawLineForeground(LineDrawInfo lineInfo, int paintX, int paintY, GC gc, Color widgetForeground, int[] selectionRanges) {
int lineLength = lineInfo.text.length();
gc.setForeground(widgetForeground);
Point[] selection = intersectingRelativeNonEmptySelections(lineInfo.offset, lineInfo.offset + lineLength);
Point[] selection = intersectingRelativeNonEmptySelections(lineInfo.offset, lineInfo.offset + lineLength, selectionRanges);
if (styledText.getBlockSelection() || selection.length == 0) {
lineInfo.layout.draw(gc, paintX, paintY);
} else {
Expand Down Expand Up @@ -614,16 +615,15 @@ private void drawLineForeground(LineDrawInfo lineInfo, int paintX, int paintY, G
}
}

private Point[] intersectingRelativeNonEmptySelections(int fromOffset, int toOffset) {
int[] selectionRanges = styledText.getSelectionRanges();
private Point[] intersectingRelativeNonEmptySelections(int fromOffset, int toOffset, int[] selectionRanges) {
int lineLength = toOffset - fromOffset;
List<Point> res = new ArrayList<>();
for (int i = 0; i < selectionRanges.length; i += 2) {
// ranges are assumed to be sorted by start offset, then (positive)length or higher end offset
Point relativeSelection = new Point(selectionRanges[i] - fromOffset, selectionRanges[i] + selectionRanges[i + 1] - fromOffset);
if (relativeSelection.x != relativeSelection.y &&
relativeSelection.x <= lineLength && relativeSelection.y >= 0) {
res.add(relativeSelection);
// ranges are assumed to be sorted by start offset, then (positive) length or higher end offset
final int x = selectionRanges[i] - fromOffset;
final int y = selectionRanges[i] + selectionRanges[i + 1] - fromOffset;
if (x != y && x <= lineLength && y >= 0) {
res.add(new Point(x, y));
}
}
return res.toArray(new Point[res.size()]);
Expand Down
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