Fixes #38591

src/vs/editor/browser/viewParts/selections/selections.ts

@@ -78,6 +78,7 @@ export class SelectionsOverlay extends DynamicViewOverlay {
 	private _context: ViewContext;
 	private _lineHeight: number;
 	private _roundedSelection: boolean;
+	private _typicalHalfwidthCharacterWidth: number;
 	private _selections: Range[];
 	private _renderResult: string[];
 
@@ -86,6 +87,7 @@ export class SelectionsOverlay extends DynamicViewOverlay {
 		this._context = context;
 		this._lineHeight = this._context.configuration.editor.lineHeight;
 		this._roundedSelection = this._context.configuration.editor.viewInfo.roundedSelection;
+		this._typicalHalfwidthCharacterWidth = this._context.configuration.editor.fontInfo.typicalHalfwidthCharacterWidth;
 		this._selections = [];
 		this._renderResult = null;
 		this._context.addEventHandler(this);
@@ -108,6 +110,9 @@ export class SelectionsOverlay extends DynamicViewOverlay {
 		if (e.viewInfo) {
 			this._roundedSelection = this._context.configuration.editor.viewInfo.roundedSelection;
 		}
+		if (e.fontInfo) {
+			this._typicalHalfwidthCharacterWidth = this._context.configuration.editor.fontInfo.typicalHalfwidthCharacterWidth;
+		}
 		return true;
 	}
 	public onCursorStateChanged(e: viewEvents.ViewCursorStateChangedEvent): boolean {
@@ -154,6 +159,7 @@ export class SelectionsOverlay extends DynamicViewOverlay {
 	}
 
 	private _enrichVisibleRangesWithStyle(linesVisibleRanges: LineVisibleRangesWithStyle[], previousFrame: LineVisibleRangesWithStyle[]): void {
+		const epsilon = this._typicalHalfwidthCharacterWidth / 4;
 		let previousFrameTop: HorizontalRangeWithStyle = null;
 		let previousFrameBottom: HorizontalRangeWithStyle = null;
 
@@ -202,13 +208,13 @@ export class SelectionsOverlay extends DynamicViewOverlay {
 				let prevLeft = linesVisibleRanges[i - 1].ranges[0].left;
 				let prevRight = linesVisibleRanges[i - 1].ranges[0].left + linesVisibleRanges[i - 1].ranges[0].width;
 
-				if (curLeft === prevLeft) {
+				if (abs(curLeft - prevLeft) < epsilon) {
 					startStyle.top = CornerStyle.FLAT;
 				} else if (curLeft > prevLeft) {
 					startStyle.top = CornerStyle.INTERN;
 				}
 
-				if (curRight === prevRight) {
+				if (abs(curRight - prevRight) < epsilon) {
 					endStyle.top = CornerStyle.FLAT;
 				} else if (prevLeft < curRight && curRight < prevRight) {
 					endStyle.top = CornerStyle.INTERN;
@@ -224,13 +230,13 @@ export class SelectionsOverlay extends DynamicViewOverlay {
 				let nextLeft = linesVisibleRanges[i + 1].ranges[0].left;
 				let nextRight = linesVisibleRanges[i + 1].ranges[0].left + linesVisibleRanges[i + 1].ranges[0].width;
 
-				if (curLeft === nextLeft) {
+				if (abs(curLeft - nextLeft) < epsilon) {
 					startStyle.bottom = CornerStyle.FLAT;
 				} else if (nextLeft < curLeft && curLeft < nextRight) {
 					startStyle.bottom = CornerStyle.INTERN;
 				}
 
-				if (curRight === nextRight) {
+				if (abs(curRight - nextRight) < epsilon) {
 					endStyle.bottom = CornerStyle.FLAT;
 				} else if (curRight < nextRight) {
 					endStyle.bottom = CornerStyle.INTERN;
@@ -407,3 +413,7 @@ registerThemingParticipant((theme, collector) => {
 		collector.addRule(`.monaco-editor .view-line span.inline-selected-text { color: ${editorSelectionForegroundColor}; }`);
 	}
 });
+
+function abs(n: number): number {
+	return n < 0 ? -n : n;
+}
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