[core] CP "Mark allow-overlap symbols visible even outside of collision grid"

platform/android/CHANGELOG.md

@@ -5,6 +5,7 @@ Mapbox welcomes participation and contributions from everyone.  If you'd like to
 ## master
 
 - Fixed a cubic-bezier interpolation bug. ([#12812] (https://github.com/mapbox/mapbox-gl-native/issues/12812))
+- Fixed an issue that could cause "allow-overlap" symbols to fade in during pan operations instead of always showing. ([#12683] (https://github.com/mapbox/mapbox-gl-native/issues/12683))
 
 ## 6.5.0-beta.1 - September 5, 2018
  - Retain shared thread pool reference [#12811](https://github.com/mapbox/mapbox-gl-native/pull/12811)

platform/ios/CHANGELOG.md

@@ -30,6 +30,7 @@ Mapbox welcomes participation and contributions from everyone. Please read [CONT
 * Fixed a crash that occurred during power state changes. ([#12584](https://github.com/mapbox/mapbox-gl-native/pull/12584))
 * Fixed a crash related to telemetry upload. ([#12584](https://github.com/mapbox/mapbox-gl-native/pull/12584))
 * Fixed a cubic-bezier interpolation bug. ([#12812] (https://github.com/mapbox/mapbox-gl-native/issues/12812))
+* Fixed an issue that could cause "allow-overlap" symbols to fade in during pan operations instead of always showing. ([#12683] (https://github.com/mapbox/mapbox-gl-native/issues/12683))
 
 ## 4.3.0 - August 15, 2018
 

platform/macos/CHANGELOG.md

@@ -22,6 +22,7 @@
 * Added an `-[MGLMapViewDelegate mapView:shapeAnnotationIsEnabled:]` method to specify whether an annotation is selectable. ([#12352](https://github.com/mapbox/mapbox-gl-native/pull/12352))
 * Fixed inconsistencies in exception naming. ([#12583](https://github.com/mapbox/mapbox-gl-native/issues/12583))
 * Fixed a cubic-bezier interpolation bug. ([#12812] (https://github.com/mapbox/mapbox-gl-native/issues/12812))
+* Fixed an issue that could cause "allow-overlap" symbols to fade in during pan operations instead of always showing. ([#12683] (https://github.com/mapbox/mapbox-gl-native/issues/12683))
 
 # 0.10.0 - August 15, 2018
 

platform/node/CHANGELOG.md

@@ -6,6 +6,7 @@
 - Added support for rendering `symbol-placement: line-center` ([#12337](https://github.com/mapbox/mapbox-gl-native/pull/12337))
 - Add support for feature expressions in `line-pattern`, `fill-pattern`, and `fill-extrusion-pattern` properties. [#12284](https://github.com/mapbox/mapbox-gl-native/pull/12284)
 - Fixed a cubic-bezier interpolation bug. ([#12812] (https://github.com/mapbox/mapbox-gl-native/issues/12812))
+- Fixed an issue that could cause "allow-overlap" symbols to fade in during pan operations instead of always showing. ([#12683] (https://github.com/mapbox/mapbox-gl-native/issues/12683))
 
 # 3.5.8 - October 19, 2017
 - Fixes an issue that causes memory leaks when not deleting the frontend object

src/mbgl/text/placement.cpp

@@ -117,6 +117,25 @@ void Placement::placeLayerBucket(
         avoidEdges = collisionIndex.projectTileBoundaries(posMatrix);
     }
 
+    const bool textAllowOverlap = bucket.layout.get<style::TextAllowOverlap>();
+    const bool iconAllowOverlap = bucket.layout.get<style::IconAllowOverlap>();
+    // This logic is similar to the "defaultOpacityState" logic below in updateBucketOpacities
+    // If we know a symbol is always supposed to show, force it to be marked visible even if
+    // it wasn't placed into the collision index (because some or all of it was outside the range
+    // of the collision grid).
+    // There is a subtle edge case here we're accepting:
+    //  Symbol A has text-allow-overlap: true, icon-allow-overlap: true, icon-optional: false
+    //  A's icon is outside the grid, so doesn't get placed
+    //  A's text would be inside grid, but doesn't get placed because of icon-optional: false
+    //  We still show A because of the allow-overlap settings.
+    //  Symbol B has allow-overlap: false, and gets placed where A's text would be
+    //  On panning in, there is a short period when Symbol B and Symbol A will overlap
+    //  This is the reverse of our normal policy of "fade in on pan", but should look like any other
+    //  collision and hopefully not be too noticeable.
+    // 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>());
+
     for (auto& symbolInstance : bucket.symbolInstances) {
 
         if (seenCrossTileIDs.count(symbolInstance.crossTileID) == 0) {
@@ -187,7 +206,7 @@ void Placement::placeLayerBucket(
                 placements.erase(symbolInstance.crossTileID);
             }
 
-            placements.emplace(symbolInstance.crossTileID, JointPlacement(placeText, placeIcon, offscreen || bucket.justReloaded));
+            placements.emplace(symbolInstance.crossTileID, JointPlacement(placeText || alwaysShowText, placeIcon || alwaysShowIcon, offscreen || bucket.justReloaded));
             seenCrossTileIDs.insert(symbolInstance.crossTileID);
         }
     }