src/vs/editor/common/viewLayout/linesLayout.ts/LinesLayout/getWhitespaceViewportData
class LinesLayout:	public getWhitespaceViewportData(verticalOffset1: number, verticalOffset2: number): IViewWhitespaceViewportData[] {
		this._checkPendingChanges();
		verticalOffset1 = verticalOffset1 | 0;
		verticalOffset2 = verticalOffset2 | 0;

		const startIndex = this.getWhitespaceIndexAtOrAfterVerticallOffset(verticalOffset1);
		const endIndex = this.getWhitespacesCount() - 1;

		if (startIndex < 0) {
			return [];
		}

		const result: IViewWhitespaceViewportData[] = [];
		for (let i = startIndex; i <= endIndex; i++) {
			const top = this.getVerticalOffsetForWhitespaceIndex(i);
			const height = this.getHeightForWhitespaceIndex(i);
			if (top >= verticalOffset2) {
				break;
			}

			result.push({
				id: this.getIdForWhitespaceIndex(i),
				afterLineNumber: this.getAfterLineNumberForWhitespaceIndex(i),
				verticalOffset: top,
				height: height
			});
		}

		return result;
	}