[core] Introduce variable text placement for point labels - Placement part

10 files changed, 267 insertions, 73 deletions

diff --git a/src/mbgl/layout/symbol_layout.cpp b/src/mbgl/layout/symbol_layout.cpp
index 52ec2aa843..f691d406f1 100644
--- a/src/mbgl/layout/symbol_layout.cpp
+++ b/src/mbgl/layout/symbol_layout.cpp
@@ -739,7 +739,7 @@ void SymbolLayout::addToDebugBuffers(SymbolBucket& bucket) {
 
                 // Dynamic vertices are initialized so that the vertex count always agrees with
                 // the layout vertex buffer, but they will always be updated before rendering happens
-                auto dynamicVertex = CollisionBoxProgram::dynamicVertex(false, false);
+                auto dynamicVertex = CollisionBoxProgram::dynamicVertex(false, false, {});
                 collisionBuffer.dynamicVertices.emplace_back(dynamicVertex);
                 collisionBuffer.dynamicVertices.emplace_back(dynamicVertex);
                 collisionBuffer.dynamicVertices.emplace_back(dynamicVertex);
diff --git a/src/mbgl/programs/collision_box_program.hpp b/src/mbgl/programs/collision_box_program.hpp
index 7b81752a94..9f1da81a1a 100644
--- a/src/mbgl/programs/collision_box_program.hpp
+++ b/src/mbgl/programs/collision_box_program.hpp
@@ -13,10 +13,9 @@ namespace mbgl {
 using CollisionBoxLayoutAttributes = TypeList<
     attributes::a_pos,
     attributes::a_anchor_pos,
-    attributes::a_extrude,
-    attributes::a_shift>;
+    attributes::a_extrude>;
 
-using CollisionBoxDynamicAttributes = TypeList<attributes::a_placed>;
+using CollisionBoxDynamicAttributes = TypeList<attributes::a_placed, attributes::a_shift>;
 
 class CollisionBoxProgram : public Program<
     CollisionBoxProgram,
@@ -45,17 +44,14 @@ public:
             {{
                 static_cast<int16_t>(::round(o.x)),
                 static_cast<int16_t>(::round(o.y))
-            }},
-            {{
-                0.0f,
-                0.0f
             }}
         };
     }
 
-    static gfx::Vertex<CollisionBoxDynamicAttributes> dynamicVertex(bool placed, bool notUsed) {
+    static gfx::Vertex<CollisionBoxDynamicAttributes> dynamicVertex(bool placed, bool notUsed, Point<float> shift) {
         return {
-            {{ static_cast<uint8_t>(placed), static_cast<uint8_t>(notUsed)  }}
+            {{ static_cast<uint8_t>(placed), static_cast<uint8_t>(notUsed)  }},
+            {{ shift.x, shift.y }}
         };
     }
 
@@ -139,10 +135,6 @@ public:
             {{
                 static_cast<int16_t>(::round(o.x)),
                 static_cast<int16_t>(::round(o.y))
-            }},
-            {{
-                0.0f,
-                0.0f
             }}
         };
     }
diff --git a/src/mbgl/renderer/layers/render_symbol_layer.cpp b/src/mbgl/renderer/layers/render_symbol_layer.cpp
index ef18a21005..ff035ab04b 100644
--- a/src/mbgl/renderer/layers/render_symbol_layer.cpp
+++ b/src/mbgl/renderer/layers/render_symbol_layer.cpp
@@ -258,8 +258,8 @@ void RenderSymbolLayer::render(PaintParameters& parameters, RenderSource*) {
                 for (const PlacedSymbol& symbol : bucket.text.placedSymbols) {
                     optional<VariableOffset> variableOffset;
                     if (!symbol.hidden && symbol.crossTileID != 0u) {
-                        auto it = parameters.variableOffsets.find(symbol.crossTileID);
-                        if (it != parameters.variableOffsets.end()) {
+                        auto it = parameters.variableOffsets.get().find(symbol.crossTileID);
+                        if (it != parameters.variableOffsets.get().end()) {
                             variableOffset = it->second;
                             hasVariablePacement |= true;
                         }
diff --git a/src/mbgl/renderer/paint_parameters.cpp b/src/mbgl/renderer/paint_parameters.cpp
index 2237b016d2..1f858ca105 100644
--- a/src/mbgl/renderer/paint_parameters.cpp
+++ b/src/mbgl/renderer/paint_parameters.cpp
@@ -13,7 +13,8 @@ PaintParameters::PaintParameters(gl::Context& context_,
                     const EvaluatedLight& evaluatedLight_,
                     RenderStaticData& staticData_,
                     ImageManager& imageManager_,
-                    LineAtlas& lineAtlas_)
+                    LineAtlas& lineAtlas_,
+                    Placement::VariableOffsets variableOffsets_)
     : context(context_),
     backend(backend_),
     state(updateParameters.transformState),
@@ -26,6 +27,7 @@ PaintParameters::PaintParameters(gl::Context& context_,
     contextMode(contextMode_),
     timePoint(updateParameters.timePoint),
     pixelRatio(pixelRatio_),
+    variableOffsets(variableOffsets_),
 #ifndef NDEBUG
     programs((debugOptions & MapDebugOptions::Overdraw) ? staticData_.overdrawPrograms : staticData_.programs)
 #else
diff --git a/src/mbgl/renderer/paint_parameters.hpp b/src/mbgl/renderer/paint_parameters.hpp
index 0b729d102b..553b4f94bf 100644
--- a/src/mbgl/renderer/paint_parameters.hpp
+++ b/src/mbgl/renderer/paint_parameters.hpp
@@ -38,7 +38,8 @@ public:
                     const EvaluatedLight&,
                     RenderStaticData&,
                     ImageManager&,
-                    LineAtlas&);
+                    LineAtlas&,
+                    Placement::VariableOffsets);
 
     gl::Context& context;
     RendererBackend& backend;
@@ -57,7 +58,7 @@ public:
     TimePoint timePoint;
 
     float pixelRatio;
-    std::unordered_map<uint32_t, VariableOffset> variableOffsets;
+    Placement::VariableOffsets variableOffsets;
     std::array<float, 2> pixelsToGLUnits;
     algorithm::ClipIDGenerator clipIDGenerator;
 
diff --git a/src/mbgl/renderer/renderer_impl.cpp b/src/mbgl/renderer/renderer_impl.cpp
index 471536cf40..19635c7784 100644
--- a/src/mbgl/renderer/renderer_impl.cpp
+++ b/src/mbgl/renderer/renderer_impl.cpp
@@ -262,7 +262,8 @@ void Renderer::Impl::render(const UpdateParameters& updateParameters) {
         renderLight.getEvaluated(),
         *staticData,
         *imageManager,
-        *lineAtlas
+        *lineAtlas,
+        placement->getVariableOffsets()
     };
 
     bool loaded = updateParameters.styleLoaded && isLoaded();
@@ -340,26 +341,25 @@ void Renderer::Impl::render(const UpdateParameters& updateParameters) {
 
         bool symbolBucketsChanged = false;
         const bool placementChanged = !placement->stillRecent(parameters.timePoint);
-        std::unique_ptr<Placement> newPlacement;
         std::set<std::string> usedSymbolLayers;
 
         if (placementChanged) {
-            newPlacement = std::make_unique<Placement>(parameters.state, parameters.mapMode, updateParameters.transitionOptions, updateParameters.crossSourceCollisions);
+            placement = std::make_unique<Placement>(parameters.state, parameters.mapMode, updateParameters.transitionOptions, updateParameters.crossSourceCollisions, std::move(placement));
         }
 
         for (const auto& item : renderItemsWithSymbols) {
             if (crossTileSymbolIndex.addLayer(*item.layer.getSymbolInterface(), parameters.state.getLatLng().longitude())) symbolBucketsChanged = true;
 
-            if (newPlacement) {
+            if (placementChanged) {
                 usedSymbolLayers.insert(item.layer.getID());
-                newPlacement->placeLayer(*item.layer.getSymbolInterface(), parameters.projMatrix, parameters.debugOptions & MapDebugOptions::Collision);
+                placement->placeLayer(*item.layer.getSymbolInterface(), parameters.projMatrix, parameters.debugOptions & MapDebugOptions::Collision);
             }
         }
 
-        if (newPlacement) {
-            newPlacement->commit(*placement, parameters.timePoint);
+        if (placementChanged) {
+            placement->commit(parameters.timePoint);
             crossTileSymbolIndex.pruneUnusedLayers(usedSymbolLayers);
-            placement = std::move(newPlacement);
+            parameters.variableOffsets = placement->getVariableOffsets();
             updateFadingTiles();
         } else {
             placement->setStale();
diff --git a/src/mbgl/text/collision_index.cpp b/src/mbgl/text/collision_index.cpp
index 90acb2b441..88e59bf51c 100644
--- a/src/mbgl/text/collision_index.cpp
+++ b/src/mbgl/text/collision_index.cpp
@@ -80,6 +80,7 @@ bool CollisionIndex::isInsideTile(const CollisionBox& box, const CollisionTileBo
 
 
 std::pair<bool,bool> CollisionIndex::placeFeature(CollisionFeature& feature,
+                                      Point<float> shift,
                                       const mat4& posMatrix,
                                       const mat4& labelPlaneMatrix,
                                       const float textPixelRatio,
@@ -95,10 +96,10 @@ std::pair<bool,bool> CollisionIndex::placeFeature(CollisionFeature& feature,
         CollisionBox& box = feature.boxes.front();
         const auto projectedPoint = projectAndGetPerspectiveRatio(posMatrix, box.anchor);
         const float tileToViewport = textPixelRatio * projectedPoint.second;
-        box.px1 = box.x1 * tileToViewport + projectedPoint.first.x;
-        box.py1 = box.y1 * tileToViewport + projectedPoint.first.y;
-        box.px2 = box.x2 * tileToViewport + projectedPoint.first.x;
-        box.py2 = box.y2 * tileToViewport + projectedPoint.first.y;
+        box.px1 = (box.x1 + shift.x) * tileToViewport + projectedPoint.first.x;
+        box.py1 = (box.y1 + shift.y) * tileToViewport + projectedPoint.first.y;
+        box.px2 = (box.x2 + shift.x) * tileToViewport + projectedPoint.first.x;
+        box.py2 = (box.y2 + shift.y) * tileToViewport + projectedPoint.first.y;
     
 
         if ((avoidEdges && !isInsideTile(box, *avoidEdges)) ||
diff --git a/src/mbgl/text/collision_index.hpp b/src/mbgl/text/collision_index.hpp
index dac0aa0bf7..dd160c945c 100644
--- a/src/mbgl/text/collision_index.hpp
+++ b/src/mbgl/text/collision_index.hpp
@@ -23,6 +23,7 @@ public:
     explicit CollisionIndex(const TransformState&);
 
     std::pair<bool,bool> placeFeature(CollisionFeature& feature,
+                                      Point<float> shift,
                                       const mat4& posMatrix,
                                       const mat4& labelPlaneMatrix,
                                       const float textPixelRatio,
diff --git a/src/mbgl/text/placement.cpp b/src/mbgl/text/placement.cpp
index bb7e2d1a6c..9d0fcf7b32 100644
--- a/src/mbgl/text/placement.cpp
+++ b/src/mbgl/text/placement.cpp
@@ -1,10 +1,13 @@
 #include <mbgl/text/placement.hpp>
+
+#include <mbgl/layout/symbol_layout.hpp>
 #include <mbgl/renderer/render_layer.hpp>
 #include <mbgl/renderer/layers/render_layer_symbol_interface.hpp>
 #include <mbgl/renderer/render_tile.hpp>
 #include <mbgl/tile/geometry_tile.hpp>
 #include <mbgl/renderer/buckets/symbol_bucket.hpp>
 #include <mbgl/renderer/bucket.hpp>
+#include <mbgl/util/math.hpp>
 
 namespace mbgl {
 
@@ -55,13 +58,18 @@ const CollisionGroups::CollisionGroup& CollisionGroups::get(const std::string& s
     }
 }
 
-Placement::Placement(const TransformState& state_, MapMode mapMode_, style::TransitionOptions transitionOptions_, const bool crossSourceCollisions)
+Placement::Placement(const TransformState& state_, MapMode mapMode_, style::TransitionOptions transitionOptions_, const bool crossSourceCollisions, std::unique_ptr<Placement> prevPlacement_)
     : collisionIndex(state_)
     , state(state_)
     , mapMode(mapMode_)
     , transitionOptions(transitionOptions_)
     , collisionGroups(crossSourceCollisions)
-{}
+    , prevPlacement(std::move(prevPlacement_))
+{
+    if (prevPlacement) {
+        prevPlacement->prevPlacement.reset(); // Only hold on to one placement back
+    }
+}
 
 void Placement::placeLayer(const RenderLayerSymbolInterface& symbolInterface, const mat4& projMatrix, bool showCollisionBoxes) {
 
@@ -121,6 +129,19 @@ void Placement::placeLayer(const RenderLayerSymbolInterface& symbolInterface, co
     }
 }
 
+namespace {
+Point<float> calculateVariableLayoutOffset(style::SymbolAnchorType anchor, float width, float height, float radialOffset, float textBoxScale) {
+    AnchorAlignment alignment = AnchorAlignment::getAnchorAlignment(anchor);
+    float shiftX = -(alignment.horizontalAlign - 0.5f) * width;
+    float shiftY = -(alignment.verticalAlign - 0.5f) * height;
+    Point<float> offset = SymbolLayout::evaluateRadialOffset(anchor, radialOffset);
+    return Point<float>(
+        shiftX + offset.x * textBoxScale,
+        shiftY + offset.y * textBoxScale
+    );
+}
+} // namespace
+
 void Placement::placeLayerBucket(
         SymbolBucket& bucket,
         const mat4& posMatrix,
@@ -161,8 +182,11 @@ void Placement::placeLayerBucket(
     // See https://github.com/mapbox/mapbox-gl-native/issues/12683
     const bool alwaysShowText = textAllowOverlap && (iconAllowOverlap || !bucket.hasIconData() || bucket.layout.get<style::IconOptional>());
     const bool alwaysShowIcon = iconAllowOverlap && (textAllowOverlap || !bucket.hasTextData() || bucket.layout.get<style::TextOptional>());
+    std::vector<style::TextVariableAnchorType> variableTextAnchors = bucket.layout.get<style::TextVariableAnchor>();
+    const bool rotateWithMap = bucket.layout.get<style::TextRotationAlignment>() == style::AlignmentType::Map;
+    const bool pitchWithMap = bucket.layout.get<style::TextPitchAlignment>() == style::AlignmentType::Map;
     
-    for (auto& symbolInstance : bucket.symbolInstances) {
+    for (SymbolInstance& symbolInstance : bucket.symbolInstances) {
 
         if (seenCrossTileIDs.count(symbolInstance.crossTileID) == 0) {
             if (holdingForFade) {
@@ -175,30 +199,111 @@ void Placement::placeLayerBucket(
             bool placeText = false;
             bool placeIcon = false;
             bool offscreen = true;
-
-            if (symbolInstance.placedRightTextIndex) {
-                PlacedSymbol& placedSymbol = bucket.text.placedSymbols.at(*symbolInstance.placedRightTextIndex);
+            optional<size_t> horizontalTextIndex = symbolInstance.getDefaultHorizontalPlacedTextIndex();
+            if (horizontalTextIndex) {
+                CollisionFeature& textCollisionFeature = symbolInstance.textCollisionFeature;
+                PlacedSymbol& placedSymbol = bucket.text.placedSymbols.at(*horizontalTextIndex);
                 const float fontSize = evaluateSizeForFeature(partiallyEvaluatedTextSize, placedSymbol);
-
-                auto placed = collisionIndex.placeFeature(symbolInstance.textCollisionFeature,
-                        posMatrix, textLabelPlaneMatrix, textPixelRatio,
-                        placedSymbol, scale, fontSize,
-                        bucket.layout.get<style::TextAllowOverlap>(),
-                        bucket.layout.get<style::TextPitchAlignment>() == style::AlignmentType::Map,
-                        showCollisionBoxes, avoidEdges, collisionGroup.second);
-                placeText = placed.first;
-                offscreen &= placed.second;
+                if (variableTextAnchors.empty()) {
+                    auto placed = collisionIndex.placeFeature(textCollisionFeature, {},
+                            posMatrix, textLabelPlaneMatrix, textPixelRatio,
+                            placedSymbol, scale, fontSize,
+                            bucket.layout.get<style::TextAllowOverlap>(),
+                            pitchWithMap,
+                            showCollisionBoxes, avoidEdges, collisionGroup.second);
+                    placeText = placed.first;
+                    offscreen &= placed.second;
+                } else if (!textCollisionFeature.alongLine && !textCollisionFeature.boxes.empty()) {
+                    const CollisionBox& textBox = symbolInstance.textCollisionFeature.boxes[0];
+                    const float width = textBox.x2 - textBox.x1;
+                    const float height = textBox.y2 - textBox.y1;
+                    const float textBoxScale = symbolInstance.textBoxScale;
+
+                    // If this symbol was in the last placement, shift the previously used
+                    // anchor to the front of the anchor list.
+                    if (prevPlacement) {
+                        auto prevOffset = prevPlacement->variableOffsets.find(symbolInstance.crossTileID);
+                        if (prevOffset != prevPlacement->variableOffsets.end() &&
+                            variableTextAnchors.front() != prevOffset->second.anchor) {
+                            std::vector<style::TextVariableAnchorType> filtered;
+                            filtered.reserve(variableTextAnchors.size());
+                            filtered.push_back(prevOffset->second.anchor);
+                            for (auto anchor : variableTextAnchors) {
+                                if (anchor != prevOffset->second.anchor) {
+                                    filtered.push_back(anchor);
+                                }
+                            }
+                            variableTextAnchors = std::move(filtered);
+                        }
+                    }
+
+                    for (auto anchor : variableTextAnchors) {
+                        Point<float> shift = calculateVariableLayoutOffset(anchor, width, height, symbolInstance.radialTextOffset, textBoxScale);
+                        if (rotateWithMap) {            
+                            float angle = pitchWithMap ? state.getBearing() : -state.getBearing();
+                            shift = util::rotate(shift, angle);
+                        }
+
+                        auto placed = collisionIndex.placeFeature(textCollisionFeature, shift,
+                                                                  posMatrix, mat4(), textPixelRatio,
+                                                                  placedSymbol, scale, fontSize,
+                                                                  bucket.layout.get<style::TextAllowOverlap>(),
+                                                                  pitchWithMap,
+                                                                  showCollisionBoxes, avoidEdges, collisionGroup.second);
+
+                        if (placed.first) {
+                            assert(symbolInstance.crossTileID != 0u);
+                            optional<style::TextVariableAnchorType> prevAnchor;
+
+                            // If this label was placed in the previous placement, record the anchor position
+                            // to allow us to animate the transition
+                            if (prevPlacement) {
+                                auto prevOffset = prevPlacement->variableOffsets.find(symbolInstance.crossTileID);
+                                auto prevPlacements = prevPlacement->placements.find(symbolInstance.crossTileID);
+                                if (prevOffset != prevPlacement->variableOffsets.end() &&
+                                    prevPlacements != prevPlacement->placements.end() &&
+                                    prevPlacements->second.text) {
+                                    prevAnchor = prevOffset->second.anchor;
+                                }
+                            }
+
+                            variableOffsets.insert(std::make_pair(symbolInstance.crossTileID, VariableOffset{
+                                symbolInstance.radialTextOffset,
+                                width,
+                                height,
+                                anchor,
+                                textBoxScale,
+                                prevAnchor
+                            }));
+                            markUsedJustification(bucket, anchor, symbolInstance);
+
+                            placeText = placed.first;
+                            offscreen &= placed.second;
+                            break;
+                        }
+                    }
+
+                    // If we didn't get placed, we still need to copy our position from the last placement for
+                    // fade animations
+                    if (prevPlacement && variableOffsets.find(symbolInstance.crossTileID) == variableOffsets.end()) {
+                        auto prevOffset = prevPlacement->variableOffsets.find(symbolInstance.crossTileID);
+                        if (prevOffset != prevPlacement->variableOffsets.end()) {
+                            variableOffsets[symbolInstance.crossTileID] = prevOffset->second;
+                            markUsedJustification(bucket, prevOffset->second.anchor, symbolInstance);
+                        }
+                    }
+                }
             }
 
             if (symbolInstance.placedIconIndex) {
                 PlacedSymbol& placedSymbol = bucket.icon.placedSymbols.at(*symbolInstance.placedIconIndex);
                 const float fontSize = evaluateSizeForFeature(partiallyEvaluatedIconSize, placedSymbol);
 
-                auto placed = collisionIndex.placeFeature(symbolInstance.iconCollisionFeature,
+                auto placed = collisionIndex.placeFeature(symbolInstance.iconCollisionFeature, {},
                         posMatrix, iconLabelPlaneMatrix, textPixelRatio,
                         placedSymbol, scale, fontSize,
                         bucket.layout.get<style::IconAllowOverlap>(),
-                        bucket.layout.get<style::IconPitchAlignment>() == style::AlignmentType::Map,
+                        pitchWithMap,
                         showCollisionBoxes, avoidEdges, collisionGroup.second);
                 placeIcon = placed.first;
                 offscreen &= placed.second;
@@ -240,7 +345,8 @@ void Placement::placeLayerBucket(
     bucket.justReloaded = false;
 }
 
-void Placement::commit(const Placement& prevPlacement, TimePoint now) {
+void Placement::commit(TimePoint now) {
+    assert(prevPlacement);
     commitTime = now;
 
     bool placementChanged = false;
@@ -248,13 +354,13 @@ void Placement::commit(const Placement& prevPlacement, TimePoint now) {
     float increment = mapMode == MapMode::Continuous &&
                       transitionOptions.enablePlacementTransitions &&
                       transitionOptions.duration.value_or(util::DEFAULT_TRANSITION_DURATION) > Milliseconds(0) ?
-        std::chrono::duration<float>(commitTime - prevPlacement.commitTime) / transitionOptions.duration.value_or(util::DEFAULT_TRANSITION_DURATION) :
+        std::chrono::duration<float>(commitTime - prevPlacement->commitTime) / transitionOptions.duration.value_or(util::DEFAULT_TRANSITION_DURATION) :
         1.0;
 
     // add the opacities from the current placement, and copy their current values from the previous placement
     for (auto& jointPlacement : placements) {
-        auto prevOpacity = prevPlacement.opacities.find(jointPlacement.first);
-        if (prevOpacity != prevPlacement.opacities.end()) {
+        auto prevOpacity = prevPlacement->opacities.find(jointPlacement.first);
+        if (prevOpacity != prevPlacement->opacities.end()) {
             opacities.emplace(jointPlacement.first, JointOpacityState(prevOpacity->second, increment, jointPlacement.second.text, jointPlacement.second.icon));
             placementChanged = placementChanged ||
                 jointPlacement.second.icon != prevOpacity->second.icon.placed ||
@@ -266,7 +372,7 @@ void Placement::commit(const Placement& prevPlacement, TimePoint now) {
     }
 
     // copy and update values from the previous placement that aren't in the current placement but haven't finished fading
-    for (auto& prevOpacity : prevPlacement.opacities) {
+    for (auto& prevOpacity : prevPlacement->opacities) {
         if (opacities.find(prevOpacity.first) == opacities.end()) {
             JointOpacityState jointOpacity(prevOpacity.second, increment, false, false);
             if (!jointOpacity.isHidden()) {
@@ -276,7 +382,16 @@ void Placement::commit(const Placement& prevPlacement, TimePoint now) {
         }
     }
 
-    fadeStartTime = placementChanged ? commitTime : prevPlacement.fadeStartTime;
+    for (auto& prevOffset : prevPlacement->variableOffsets) {
+        const uint32_t crossTileID = prevOffset.first;
+        auto foundOffset = variableOffsets.find(crossTileID);
+        auto foundOpacity = opacities.find(crossTileID);
+        if (foundOffset == variableOffsets.end() && foundOpacity != opacities.end() && !foundOpacity->second.isHidden()) {
+            variableOffsets[prevOffset.first] = prevOffset.second;
+        }
+    }
+
+    fadeStartTime = placementChanged ? commitTime : prevPlacement->fadeStartTime;
 }
 
 void Placement::updateLayerOpacities(const RenderLayerSymbolInterface& symbolInterface) {
@@ -310,7 +425,10 @@ void Placement::updateBucketOpacities(SymbolBucket& bucket, std::set<uint32_t>&
 
     const bool textAllowOverlap = bucket.layout.get<style::TextAllowOverlap>();
     const bool iconAllowOverlap = bucket.layout.get<style::IconAllowOverlap>();
-    
+    const bool variablePlacement = !bucket.layout.get<style::TextVariableAnchor>().empty();
+    const bool rotateWithMap = bucket.layout.get<style::TextRotationAlignment>() == style::AlignmentType::Map;
+    const bool pitchWithMap = bucket.layout.get<style::TextPitchAlignment>() == style::AlignmentType::Map;
+
     // If allow-overlap is true, we can show symbols before placement runs on them
     // But we have to wait for placement if we potentially depend on a paired icon/text
     // with allow-overlap: false.
@@ -339,19 +457,38 @@ void Placement::updateBucketOpacities(SymbolBucket& bucket, std::set<uint32_t>&
 
         if (symbolInstance.hasText) {
             auto opacityVertex = SymbolSDFTextProgram::opacityVertex(opacityState.text.placed, opacityState.text.opacity);
-            for (size_t i = 0; i < symbolInstance.rightJustifiedGlyphQuads.size() * 4; i++) {
-                bucket.text.opacityVertices.emplace_back(opacityVertex);
-            }
-            for (size_t i = 0; i < symbolInstance.verticalGlyphQuads.size() * 4; i++) {
-                bucket.text.opacityVertices.emplace_back(opacityVertex);
-            }
             if (symbolInstance.placedRightTextIndex) {
+                for (size_t i = 0; i < symbolInstance.rightJustifiedGlyphQuads.size() * 4; i++) {
+                    bucket.text.opacityVertices.emplace_back(opacityVertex);
+                }
                 PlacedSymbol& placed = bucket.text.placedSymbols[*symbolInstance.placedRightTextIndex];
                 placed.hidden = opacityState.isHidden();
             }
+            if (symbolInstance.placedCenterTextIndex) {
+                for (size_t i = 0; i < symbolInstance.centerJustifiedGlyphQuads.size() * 4; i++) {
+                    bucket.text.opacityVertices.emplace_back(opacityVertex);
+                }
+                PlacedSymbol& placed = bucket.text.placedSymbols[*symbolInstance.placedCenterTextIndex];
+                placed.hidden = opacityState.isHidden();
+            }
+            if (symbolInstance.placedLeftTextIndex) {
+                for (size_t i = 0; i < symbolInstance.leftJustifiedGlyphQuads.size() * 4; i++) {
+                    bucket.text.opacityVertices.emplace_back(opacityVertex);
+                }
+                PlacedSymbol& placed = bucket.text.placedSymbols[*symbolInstance.placedLeftTextIndex];
+                placed.hidden = opacityState.isHidden();
+            }
             if (symbolInstance.placedVerticalTextIndex) {
+                for (size_t i = 0; i < symbolInstance.verticalGlyphQuads.size() * 4; i++) {
+                    bucket.text.opacityVertices.emplace_back(opacityVertex);
+                }
                 bucket.text.placedSymbols[*symbolInstance.placedVerticalTextIndex].hidden = opacityState.isHidden();
             }
+
+            auto prevOffset = variableOffsets.find(symbolInstance.crossTileID);
+            if (prevOffset != variableOffsets.end()) {
+                markUsedJustification(bucket, prevOffset->second.anchor, symbolInstance);
+            }
         }
         if (symbolInstance.hasIcon) {
             auto opacityVertex = SymbolIconProgram::opacityVertex(opacityState.icon.placed, opacityState.icon.opacity);
@@ -370,7 +507,42 @@ void Placement::updateBucketOpacities(SymbolBucket& bucket, std::set<uint32_t>&
             if (feature.alongLine) {
                 return;
             }
-            auto dynamicVertex = CollisionBoxProgram::dynamicVertex(placed, false);
+            auto dynamicVertex = CollisionBoxProgram::dynamicVertex(placed, false, {});
+            for (size_t i = 0; i < feature.boxes.size() * 4; i++) {
+                bucket.collisionBox.dynamicVertices.emplace_back(dynamicVertex);
+            }
+        };
+
+        auto updateCollisionTextBox = [this, &bucket, &symbolInstance, variablePlacement, rotateWithMap, pitchWithMap](const auto& feature, const bool placed) {
+            if (feature.alongLine) {
+                return;
+            }
+            Point<float> shift;
+            bool used = true;
+            if (variablePlacement) {
+                auto foundOffset = variableOffsets.find(symbolInstance.crossTileID);
+                if (foundOffset != variableOffsets.end()) {
+                    const VariableOffset& variableOffset = foundOffset->second;
+                    // This will show either the currently placed position or the last
+                    // successfully placed position (so you can visualize what collision
+                    // just made the symbol disappear, and the most likely place for the
+                    // symbol to come back)
+                    shift = calculateVariableLayoutOffset(variableOffset.anchor,
+                                                          variableOffset.width,
+                                                          variableOffset.height,
+                                                          variableOffset.radialOffset,
+                                                          variableOffset.textBoxScale);
+                    if (rotateWithMap) {
+                        shift = util::rotate(shift, pitchWithMap ? state.getBearing() : -state.getBearing());
+                    }
+                } else {
+                    // No offset -> this symbol hasn't been placed since coming on-screen
+                    // No single box is particularly meaningful and all of them would be too noisy
+                    // Use the center box just to show something's there, but mark it "not used"
+                    used = false;
+                }
+            }
+            auto dynamicVertex = CollisionBoxProgram::dynamicVertex(placed, !used, shift);
             for (size_t i = 0; i < feature.boxes.size() * 4; i++) {
                 bucket.collisionBox.dynamicVertices.emplace_back(dynamicVertex);
             }
@@ -381,7 +553,7 @@ void Placement::updateBucketOpacities(SymbolBucket& bucket, std::set<uint32_t>&
                 return;
             }
             for (const CollisionBox& box : feature.boxes) {
-                auto dynamicVertex = CollisionBoxProgram::dynamicVertex(placed, !box.used);
+                auto dynamicVertex = CollisionBoxProgram::dynamicVertex(placed, !box.used, {});
                 bucket.collisionCircle.dynamicVertices.emplace_back(dynamicVertex);
                 bucket.collisionCircle.dynamicVertices.emplace_back(dynamicVertex);
                 bucket.collisionCircle.dynamicVertices.emplace_back(dynamicVertex);
@@ -390,7 +562,7 @@ void Placement::updateBucketOpacities(SymbolBucket& bucket, std::set<uint32_t>&
         };
         
         if (bucket.hasCollisionBoxData()) {
-            updateCollisionBox(symbolInstance.textCollisionFeature, opacityState.text.placed);
+            updateCollisionTextBox(symbolInstance.textCollisionFeature, opacityState.text.placed);
             updateCollisionBox(symbolInstance.iconCollisionFeature, opacityState.icon.placed);
         }
         if (bucket.hasCollisionCircleData()) {
@@ -407,6 +579,31 @@ void Placement::updateBucketOpacities(SymbolBucket& bucket, std::set<uint32_t>&
     }
 }
 
+void Placement::markUsedJustification(SymbolBucket& bucket, style::TextVariableAnchorType placedAnchor, SymbolInstance& symbolInstance) {
+    std::map<style::TextJustifyType, optional<size_t>> justificationToIndex {
+                {style::TextJustifyType::Right, symbolInstance.placedRightTextIndex},
+                {style::TextJustifyType::Center, symbolInstance.placedCenterTextIndex},
+                {style::TextJustifyType::Left, symbolInstance.placedLeftTextIndex},
+            };
+    style::TextJustifyType justify = getAnchorJustification(placedAnchor);
+    assert(justify == style::TextJustifyType::Right || justify == style::TextJustifyType::Center || justify == style::TextJustifyType::Left);
+    const optional<size_t> autoIndex = justificationToIndex[justify];
+
+    for (auto& pair : justificationToIndex) {
+        const optional<size_t> index = pair.second;
+        if (index) {
+            assert(bucket.text.placedSymbols.size() > *index);
+            if (autoIndex && *index != *autoIndex) {
+                // There are multiple justifications and this one isn't it: shift offscreen
+                bucket.text.placedSymbols.at(*index).crossTileID = 0u;
+            } else {
+                // Either this is the chosen justification or the justification is hardwired: use this one
+                bucket.text.placedSymbols.at(*index).crossTileID = symbolInstance.crossTileID;
+            }
+        }
+    }
+}
+
 float Placement::symbolFadeChange(TimePoint now) const {
     if (mapMode == MapMode::Continuous && transitionOptions.enablePlacementTransitions &&
         transitionOptions.duration.value_or(util::DEFAULT_TRANSITION_DURATION) > Milliseconds(0)) {
diff --git a/src/mbgl/text/placement.hpp b/src/mbgl/text/placement.hpp
index 673ea59c24..3f2a7b8a03 100644
--- a/src/mbgl/text/placement.hpp
+++ b/src/mbgl/text/placement.hpp
@@ -12,6 +12,7 @@ namespace mbgl {
 
 class RenderLayerSymbolInterface;
 class SymbolBucket;
+class SymbolInstance;
 
 class OpacityState {
 public:
@@ -90,9 +91,9 @@ private:
     
 class Placement {
 public:
-    Placement(const TransformState&, MapMode, style::TransitionOptions, const bool crossSourceCollisions);
+    Placement(const TransformState&, MapMode, style::TransitionOptions, const bool crossSourceCollisions, std::unique_ptr<Placement> prevPlacementOrNull = nullptr);
     void placeLayer(const RenderLayerSymbolInterface&, const mat4&, bool showCollisionBoxes);
-    void commit(const Placement& prevPlacement, TimePoint);
+    void commit(TimePoint);
     void updateLayerOpacities(const RenderLayerSymbolInterface&);
     float symbolFadeChange(TimePoint now) const;
     bool hasTransitions(TimePoint now) const;
@@ -104,8 +105,10 @@ public:
     void setStale();
     
     const RetainedQueryData& getQueryData(uint32_t bucketInstanceId) const;
-private:
+    using VariableOffsets = std::reference_wrapper<const std::unordered_map<uint32_t, VariableOffset>>;
+    VariableOffsets getVariableOffsets() const { return std::cref(variableOffsets); }
 
+private:
     void placeLayerBucket(
             SymbolBucket&,
             const mat4& posMatrix,
@@ -119,6 +122,7 @@ private:
             const CollisionGroups::CollisionGroup& collisionGroup);
 
     void updateBucketOpacities(SymbolBucket&, std::set<uint32_t>&);
+    void markUsedJustification(SymbolBucket&, style::TextVariableAnchorType, SymbolInstance&);
 
     CollisionIndex collisionIndex;
 
@@ -131,17 +135,13 @@ private:
 
     std::unordered_map<uint32_t, JointPlacement> placements;
     std::unordered_map<uint32_t, JointOpacityState> opacities;
+    std::unordered_map<uint32_t, VariableOffset> variableOffsets;
 
     bool stale = false;
     
     std::unordered_map<uint32_t, RetainedQueryData> retainedQueryData;
     CollisionGroups collisionGroups;
+    std::unique_ptr<Placement> prevPlacement;
 };
 
-Point<float> calculateVariableLayoutOffset(style::SymbolAnchorType anchor,
-                                           float width,
-                                           float height,
-                                           float radialOffset,
-                                           float textBoxScale);
-
 } // namespace mbgl