From 39e1c86ae94f150b5d2a9687ebdd91647c87d11d Mon Sep 17 00:00:00 2001
From: Petr Pokorny <petr-pokorny@hotmail.com>
Date: Sun, 28 Feb 2021 19:01:03 +0100
Subject: [PATCH] fixes #16

---
 src/mbgl/renderer/layers/render_symbol_layer.cpp |  3 ++-
 src/mbgl/text/placement.cpp                      | 14 +++++++++++---
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/mbgl/renderer/layers/render_symbol_layer.cpp b/src/mbgl/renderer/layers/render_symbol_layer.cpp
index 1d8c0a70a..d70d10d6f 100644
--- a/src/mbgl/renderer/layers/render_symbol_layer.cpp
+++ b/src/mbgl/renderer/layers/render_symbol_layer.cpp
@@ -424,7 +424,8 @@ void RenderSymbolLayer::render(PaintParameters& parameters) {
         assert(bucket.paintProperties.find(getID()) != bucket.paintProperties.end());
         const auto& bucketPaintProperties = bucket.paintProperties.at(getID());
 
-        bucket.justReloaded = false;
+        // Prevent a flickering issue when a symbol is moved.
+        // bucket.justReloaded = false;
 
         auto addRenderables = [&renderableSegments, &tile, renderData, &bucketPaintProperties, it = renderableSegments.begin()] (auto& segments, const SymbolType type) mutable {
             for (auto& segment : segments) {
diff --git a/src/mbgl/text/placement.cpp b/src/mbgl/text/placement.cpp
index f98039dec..c3072b05c 100644
--- a/src/mbgl/text/placement.cpp
+++ b/src/mbgl/text/placement.cpp
@@ -241,9 +241,16 @@ void Placement::placeSymbolBucket(const BucketPlacementData& params, std::set<ui
     for (const SymbolInstance& symbol : getSortedSymbols(params, ctx.pixelRatio)) {
         if (seenCrossTileIDs.count(symbol.crossTileID) != 0u) continue;
         placeSymbol(symbol, ctx);
-        seenCrossTileIDs.insert(symbol.crossTileID);
+
+        // Prevent a flickering issue while zooming out.
+        if (symbol.crossTileID != SymbolInstance::invalidCrossTileID() && !ctx.getRenderTile().holdForFade()) {
+            seenCrossTileIDs.insert(symbol.crossTileID);
+        }        
     }
 
+    // Prevent a flickering issue when a symbol is moved.
+    symbolBucket.justReloaded = false;
+
     // As long as this placement lives, we have to hold onto this bucket's
     // matching FeatureIndex/data for querying purposes
     retainedQueryData.emplace(
@@ -905,9 +912,10 @@ void Placement::updateBucketOpacities(SymbolBucket& bucket,
     // But we have to wait for placement if we potentially depend on a paired icon/text
     // with allow-overlap: false.
     // See https://github.com/mapbox/mapbox-gl-native/issues/12483
+    // Prevent a flickering issue when showing a symbol allowing overlap.
     const JointOpacityState defaultOpacityState(
-            textAllowOverlap && (iconAllowOverlap || !(bucket.hasIconData() || bucket.hasSdfIconData()) || bucket.layout->get<style::IconOptional>()),
-            iconAllowOverlap && (textAllowOverlap || !bucket.hasTextData() || bucket.layout->get<style::TextOptional>()),
+            bucket.justReloaded && textAllowOverlap && (iconAllowOverlap || !(bucket.hasIconData() || bucket.hasSdfIconData()) || bucket.layout->get<style::IconOptional>()),
+            bucket.justReloaded && iconAllowOverlap && (textAllowOverlap || !bucket.hasTextData() || bucket.layout->get<style::TextOptional>()),
             true);
 
     for (SymbolInstance& symbolInstance : bucket.symbolInstances) {