[thanos] Tracked original gap height to fix post-deletion gap positions.

Telegram/SourceFiles/history/history_widget.cpp

@@ -7588,6 +7588,7 @@ void HistoryWidget::startCollapseAnimation(int height, int itemTop) {
 				&& itemTop <= gap.absY + gap.currentHeight)) {
 			gap.startHeight += height;
 			gap.currentHeight += height;
+			gap.originalHeight += height;
 			merged = true;
 			break;
 		}
@@ -7595,6 +7596,7 @@ void HistoryWidget::startCollapseAnimation(int height, int itemTop) {
 			gap.absY = itemTop;
 			gap.startHeight += height;
 			gap.currentHeight += height;
+			gap.originalHeight += height;
 			merged = true;
 			break;
 		}
@@ -7604,6 +7606,7 @@ void HistoryWidget::startCollapseAnimation(int height, int itemTop) {
 			.absY = itemTop,
 			.startHeight = height,
 			.currentHeight = height,
+			.originalHeight = height,
 		});
 		std::sort(_collapseGaps.begin(), _collapseGaps.end(),
 			[](const auto &a, const auto &b) { return a.absY < b.absY; });
@@ -7660,8 +7663,13 @@ void HistoryWidget::syncCollapseGapsToList() {
 	}
 	auto gaps = std::vector<HistoryInner::CollapseGap>();
 	gaps.reserve(_collapseGaps.size());
+	auto cumulativeOriginal = 0;
 	for (const auto &g : _collapseGaps) {
-		gaps.push_back({ .absY = g.absY, .height = g.currentHeight });
+		gaps.push_back({
+			.absY = g.absY - cumulativeOriginal,
+			.height = g.currentHeight,
+		});
+		cumulativeOriginal += g.originalHeight;
 	}
 	_list->setCollapseGaps(gaps);
 }

Telegram/SourceFiles/history/history_widget.h

@@ -949,6 +949,7 @@ private:
 		int absY = -1;
 		int startHeight = 0;
 		int currentHeight = 0;
+		int originalHeight = 0;
 	};
 	std::vector<CollapseGapState> _collapseGaps;
 	Ui::Animations::Simple _collapseAnimation;