Bug 569550 - Rendering vert.indent keeps caret position unchanged

When adding some vertical spacing, try to
1. keep the current visible line with caret unmoved, and,
2. if caret not visible, move either line above or below the spacing,
picking the least amount of lines moved.

Change-Id: I97a48293fd92d219706bb20268c6964e198bae3c
Signed-off-by: Mickael Istria <mistria@redhat.com>

2 files changed, 44 insertions, 12 deletions

diff --git a/bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/StyledText.java b/bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/StyledText.java
index 1acc2fcd32..231568ac04 100644
--- a/bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/StyledText.java
+++ b/bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/StyledText.java
@@ -9443,21 +9443,34 @@ public void setLineVerticalIndent(int lineIndex, int verticalLineIndent) {
 	if (lineIndex < 0 || lineIndex >= content.getLineCount()) {
 		SWT.error(SWT.ERROR_INVALID_ARGUMENT);
 	}
-	if (verticalLineIndent == renderer.getLineVerticalIndent(lineIndex)) {
-			return;
-	}
-	int oldBottom = getLinePixel(lineIndex + 1);
-	if (oldBottom <= getClientArea().height) {
-		verticalScrollOffset = -1;
+	int previousVerticalIndent = renderer.getLineVerticalIndent(lineIndex);
+	if (verticalLineIndent == previousVerticalIndent) {
+		return;
 	}
+	int initialTopPixel = getTopPixel();
+	int verticalIndentDiff = verticalLineIndent - previousVerticalIndent;
 	renderer.setLineVerticalIndent(lineIndex, verticalLineIndent);
-	hasVerticalIndent = verticalLineIndent != 0 || renderer.hasVerticalIndent();
+	this.hasVerticalIndent = verticalLineIndent != 0 || renderer.hasVerticalIndent();
 	resetCache(lineIndex, 1);
-	int newBottom = getLinePixel(lineIndex + 1);
-	redrawLines(lineIndex, 1, oldBottom != newBottom);
-	int caretLine = getCaretLine();
-	if (lineIndex <= caretLine && caretLine < lineIndex + 1) {
-		setCaretLocation();
+	if (lineIndex < getPartialTopIndex()) {
+		setTopPixel(initialTopPixel + verticalIndentDiff);
+	} else if (lineIndex > getPartialBottomIndex()) {
+		// adjust vertical scollbar
+	} else {
+		if (getCaretLine() >= getPartialTopIndex() && getCaretLine() <= getPartialBottomIndex()) { // caret line with caret mustn't move
+			if (getCaretLine() < lineIndex) {
+				redrawLines(lineIndex, getPartialBottomIndex(), true);
+			} else {
+				setTopPixel(initialTopPixel + verticalIndentDiff);
+			}
+		} else { // move as few lines as possible
+			if (lineIndex - getTopIndex() < getBottomIndex() - lineIndex) {
+				setTopPixel(initialTopPixel + verticalIndentDiff);
+			} else {
+				// redraw below
+				redrawLines(lineIndex, getPartialBottomIndex() - lineIndex + 1, true);
+			}
+		}
 	}
 }
 
diff --git a/tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_custom_StyledText.java b/tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_custom_StyledText.java
index 5f795fc9d1..302663e825 100644
--- a/tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_custom_StyledText.java
+++ b/tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_custom_StyledText.java
@@ -4925,6 +4925,25 @@ public void test_verticalIndent_changeRelativeBounds() {
 }
 
 @Test
+public void test_verticalIndent_keepsCurrentCaretAndLinePosition() throws InterruptedException {
+	String _50lines = IntStream.range(1, 50).mapToObj(Integer::toString).collect(Collectors.joining("\n"));
+	text.setText(_50lines);
+	text.setSize(500, 200);
+	int line = 30;
+	int offset = text.getOffsetAtLine(line);
+	text.setSelection(offset);
+	text.showSelection();
+	Point caretLocation = text.getCaret().getLocation();
+	Point offsetLocation = text.getLocationAtOffset(offset);
+	text.setLineVerticalIndent(line, 34);
+	assertEquals(caretLocation, text.getCaret().getLocation());
+	assertEquals(offsetLocation, text.getLocationAtOffset(offset));
+	text.setLineVerticalIndent(line, 0);
+	assertEquals(caretLocation, text.getCaret().getLocation());
+	assertEquals(offsetLocation, text.getLocationAtOffset(offset));
+}
+
+@Test
 public void test_notFixedLineHeightDoesntChangeLinePixelIfUnnecessary() {
 	String _50lines = IntStream.range(1, 50).mapToObj(Integer::toString).collect(Collectors.joining("\n"));
 	text.setText(_50lines);