[core] Implement data-driven styling for {text,icon}-{color,opacity,halo-color,halo-blur,halo-width} (#7939)

* Add symbol dds attributes and adapt style code generation

* Update to mapbox-gl-js/master

* Refactor SymbolFeature as a subclass of GeometryTileFeature

Prepares for enabling DDS on symbol paint properties by allowing the
SymbolFeatures, which we keep around after constructing SymbolLayout,
to be used in evaluating data-driven paint properties later in the
layout process.

* Draft approach for splitting icon/text paint properties

The `Program` types are set up to bind GL attributes to each of the
data-driven paint properties specified in the `PaintProperties` type
provided.  Since `SymbolPaintProperties` specifies both `Text*` and
`Icon*` properties, the symbolIcon, symbolIconSDF, and symbolGlyph
programs each attempt to bind roughly double the number of attributes
that they actually need.

This change addresses this by:
- Adding the more specific `IconPaintProperties` and `TextPaintProperties` types, which are subsets of the full `SymbolPaintProperties`.
- The symbol layer continues to use its `SymbolPaintProperties paint` member to track layer property state, but it provides helpers that construct objects of each the specific `{Icon,Text}PaintProperties::Evaluated` type, for use by the painter.
- The three symbol programs instantiate `Program<>` using the appropriate `{Icon,Text}PaintProperties` type.

* check in generated style code

* Populate paint buffers for symbol DDS properties

* Address first round of review comments

* Refactor VectorTile{Layer,Feature} to explicitly share data

* Update submodule

1 files changed, 43 insertions, 27 deletions

diff --git a/src/mbgl/tile/vector_tile.cpp b/src/mbgl/tile/vector_tile.cpp
index a195885415..68f48e81fd 100644
--- a/src/mbgl/tile/vector_tile.cpp
+++ b/src/mbgl/tile/vector_tile.cpp
@@ -15,9 +15,23 @@ class VectorTileLayer;
 
 using packed_iter_type = protozero::iterator_range<protozero::pbf_reader::const_uint32_iterator>;
 
+struct VectorTileLayerData {
+    VectorTileLayerData(std::shared_ptr<const std::string>);
+    
+    // Hold a reference to the underlying pbf data that backs the lazily-built
+    // components of the owning VectorTileLayer and VectorTileFeature objects
+    std::shared_ptr<const std::string> data;
+    
+    uint32_t version = 1;
+    uint32_t extent = 4096;
+    std::unordered_map<std::string, uint32_t> keysMap;
+    std::vector<std::reference_wrapper<const std::string>> keys;
+    std::vector<Value> values;
+};
+
 class VectorTileFeature : public GeometryTileFeature {
 public:
-    VectorTileFeature(protozero::pbf_reader, const VectorTileLayer&);
+    VectorTileFeature(protozero::pbf_reader, std::shared_ptr<VectorTileLayerData> layerData);
 
     FeatureType getType() const override { return type; }
     optional<Value> getValue(const std::string&) const override;
@@ -26,16 +40,16 @@ public:
     GeometryCollection getGeometries() const override;
 
 private:
-    const VectorTileLayer& layer;
+    std::shared_ptr<VectorTileLayerData> layerData;
     optional<FeatureIdentifier> id;
     FeatureType type = FeatureType::Unknown;
     packed_iter_type tags_iter;
     packed_iter_type geometry_iter;
 };
-
+    
 class VectorTileLayer : public GeometryTileLayer {
 public:
-    VectorTileLayer(protozero::pbf_reader);
+    VectorTileLayer(protozero::pbf_reader, std::shared_ptr<const std::string>);
 
     std::size_t featureCount() const override { return features.size(); }
     std::unique_ptr<GeometryTileFeature> getFeature(std::size_t) const override;
@@ -46,12 +60,8 @@ private:
     friend class VectorTileFeature;
 
     std::string name;
-    uint32_t version = 1;
-    uint32_t extent = 4096;
-    std::unordered_map<std::string, uint32_t> keysMap;
-    std::vector<std::reference_wrapper<const std::string>> keys;
-    std::vector<Value> values;
     std::vector<protozero::pbf_reader> features;
+    std::shared_ptr<VectorTileLayerData> data;
 };
 
 class VectorTileData : public GeometryTileData {
@@ -117,8 +127,8 @@ Value parseValue(protozero::pbf_reader data) {
     return false;
 }
 
-VectorTileFeature::VectorTileFeature(protozero::pbf_reader feature_pbf, const VectorTileLayer& layer_)
-    : layer(layer_) {
+VectorTileFeature::VectorTileFeature(protozero::pbf_reader feature_pbf, std::shared_ptr<VectorTileLayerData> layerData_)
+    : layerData(std::move(layerData_)) {
     while (feature_pbf.next()) {
         switch (feature_pbf.tag()) {
         case 1: // id
@@ -141,8 +151,8 @@ VectorTileFeature::VectorTileFeature(protozero::pbf_reader feature_pbf, const Ve
 }
 
 optional<Value> VectorTileFeature::getValue(const std::string& key) const {
-    auto keyIter = layer.keysMap.find(key);
-    if (keyIter == layer.keysMap.end()) {
+    auto keyIter = layerData->keysMap.find(key);
+    if (keyIter == layerData->keysMap.end()) {
         return optional<Value>();
     }
 
@@ -151,7 +161,7 @@ optional<Value> VectorTileFeature::getValue(const std::string& key) const {
     while (start_itr != end_itr) {
         uint32_t tag_key = static_cast<uint32_t>(*start_itr++);
 
-        if (layer.keysMap.size() <= tag_key) {
+        if (layerData->keysMap.size() <= tag_key) {
             throw std::runtime_error("feature referenced out of range key");
         }
 
@@ -160,12 +170,12 @@ optional<Value> VectorTileFeature::getValue(const std::string& key) const {
         }
 
         uint32_t tag_val = static_cast<uint32_t>(*start_itr++);;
-        if (layer.values.size() <= tag_val) {
+        if (layerData->values.size() <= tag_val) {
             throw std::runtime_error("feature referenced out of range value");
         }
 
         if (tag_key == keyIter->second) {
-            return layer.values[tag_val];
+            return layerData->values[tag_val];
         }
     }
 
@@ -182,7 +192,7 @@ std::unordered_map<std::string,Value> VectorTileFeature::getProperties() const {
             throw std::runtime_error("uneven number of feature tag ids");
         }
         uint32_t tag_val = static_cast<uint32_t>(*start_itr++);
-        properties[layer.keys.at(tag_key)] = layer.values.at(tag_val);
+        properties[layerData->keys.at(tag_key)] = layerData->values.at(tag_val);
     }
     return properties;
 }
@@ -196,7 +206,7 @@ GeometryCollection VectorTileFeature::getGeometries() const {
     uint32_t length = 0;
     int32_t x = 0;
     int32_t y = 0;
-    const float scale = float(util::EXTENT) / layer.extent;
+    const float scale = float(util::EXTENT) / layerData->extent;
 
     GeometryCollection lines;
 
@@ -234,7 +244,7 @@ GeometryCollection VectorTileFeature::getGeometries() const {
         }
     }
 
-    if (layer.version >= 2 || type != FeatureType::Polygon) {
+    if (layerData->version >= 2 || type != FeatureType::Polygon) {
         return lines;
     }
 
@@ -250,7 +260,7 @@ const GeometryTileLayer* VectorTileData::getLayer(const std::string& name) const
         parsed = true;
         protozero::pbf_reader tile_pbf(*data);
         while (tile_pbf.next(3)) {
-            VectorTileLayer layer(tile_pbf.get_message());
+            VectorTileLayer layer(tile_pbf.get_message(), data);
             layers.emplace(layer.name, std::move(layer));
         }
     }
@@ -262,7 +272,13 @@ const GeometryTileLayer* VectorTileData::getLayer(const std::string& name) const
     return nullptr;
 }
 
-VectorTileLayer::VectorTileLayer(protozero::pbf_reader layer_pbf) {
+VectorTileLayerData::VectorTileLayerData(std::shared_ptr<const std::string> pbfData) :
+    data(std::move(pbfData))
+{}
+
+VectorTileLayer::VectorTileLayer(protozero::pbf_reader layer_pbf, std::shared_ptr<const std::string> pbfData)
+    : data(std::make_shared<VectorTileLayerData>(std::move(pbfData)))
+{
     while (layer_pbf.next()) {
         switch (layer_pbf.tag()) {
         case 1: // name
@@ -273,18 +289,18 @@ VectorTileLayer::VectorTileLayer(protozero::pbf_reader layer_pbf) {
             break;
         case 3: // keys
             {
-                auto iter = keysMap.emplace(layer_pbf.get_string(), keysMap.size());
-                keys.emplace_back(std::reference_wrapper<const std::string>(iter.first->first));
+                auto iter = data->keysMap.emplace(layer_pbf.get_string(), data->keysMap.size());
+                data->keys.emplace_back(std::reference_wrapper<const std::string>(iter.first->first));
             }
             break;
         case 4: // values
-            values.emplace_back(parseValue(layer_pbf.get_message()));
+            data->values.emplace_back(parseValue(layer_pbf.get_message()));
             break;
         case 5: // extent
-            extent = layer_pbf.get_uint32();
+            data->extent = layer_pbf.get_uint32();
             break;
         case 15: // version
-            version = layer_pbf.get_uint32();
+            data->version = layer_pbf.get_uint32();
             break;
         default:
             layer_pbf.skip();
@@ -294,7 +310,7 @@ VectorTileLayer::VectorTileLayer(protozero::pbf_reader layer_pbf) {
 }
 
 std::unique_ptr<GeometryTileFeature> VectorTileLayer::getFeature(std::size_t i) const {
-    return std::make_unique<VectorTileFeature>(features.at(i), *this);
+    return std::make_unique<VectorTileFeature>(features.at(i), data);
 }
 
 std::string VectorTileLayer::getName() const {