[core] add support for mapzen terrarium (#11154)

* add support for mapzen terrarium

* Encoding --> DEMEncoding, avoid if statement when unpacking elevation values

* add Terrarium test

* update submodule

* remove redundant checks

9 files changed, 37 insertions, 10 deletions

diff --git a/src/mbgl/geometry/dem_data.cpp b/src/mbgl/geometry/dem_data.cpp
index 78134dadc1..7fa98950ea 100644
--- a/src/mbgl/geometry/dem_data.cpp
+++ b/src/mbgl/geometry/dem_data.cpp
@@ -3,7 +3,7 @@
 
 namespace mbgl {
 
-DEMData::DEMData(const PremultipliedImage& _image):
+DEMData::DEMData(const PremultipliedImage& _image, Tileset::DEMEncoding encoding):
     dim(_image.size.height),
     border(std::max<int32_t>(std::ceil(_image.size.height / 2), 1)),
     stride(dim + 2 * border),
@@ -13,13 +13,25 @@ DEMData::DEMData(const PremultipliedImage& _image):
         throw std::runtime_error("raster-dem tiles must be square.");
     }
 
+    auto decodeMapbox = [] (const uint8_t r, const uint8_t g, const uint8_t b){
+        // https://www.mapbox.com/help/access-elevation-data/#mapbox-terrain-rgb
+        return (r * 256 * 256 + g * 256 + b)/10 - 10000;
+    };
+
+    auto decodeTerrarium = [] (const uint8_t r, const uint8_t g, const uint8_t b){
+        // https://aws.amazon.com/public-datasets/terrain/
+        return ((r * 256 + g + b / 256) - 32768);
+    };
+
+    auto decodeRGB = encoding == Tileset::DEMEncoding::Terrarium ? decodeTerrarium : decodeMapbox;
+
     std::memset(image.data.get(), 0, image.bytes());
 
     for (int32_t y = 0; y < dim; y++) {
         for (int32_t x = 0; x < dim; x++) {
             const int32_t i = y * dim + x;
             const int32_t j = i * 4;
-            set(x, y, (_image.data[j] * 256 * 256 + _image.data[j+1] * 256 + _image.data[j+2])/10 - 10000);
+            set(x, y, decodeRGB(_image.data[j], _image.data[j+1], _image.data[j+2]));
         }
     }
     
diff --git a/src/mbgl/geometry/dem_data.hpp b/src/mbgl/geometry/dem_data.hpp
index 507a51661d..817d3cc9c9 100644
--- a/src/mbgl/geometry/dem_data.hpp
+++ b/src/mbgl/geometry/dem_data.hpp
@@ -2,6 +2,7 @@
 
 #include <mbgl/math/clamp.hpp>
 #include <mbgl/util/image.hpp>
+#include <mbgl/util/tileset.hpp>
 
 #include <memory>
 #include <array>
@@ -12,7 +13,7 @@ namespace mbgl {
 
 class DEMData {
 public:
-    DEMData(const PremultipliedImage& image);
+    DEMData(const PremultipliedImage& image, Tileset::DEMEncoding encoding);
     void backfillBorder(const DEMData& borderTileData, int8_t dx, int8_t dy);
 
     void set(const int32_t x, const int32_t y, const int32_t value) {
diff --git a/src/mbgl/renderer/buckets/hillshade_bucket.cpp b/src/mbgl/renderer/buckets/hillshade_bucket.cpp
index 8011681ee0..00b9536894 100644
--- a/src/mbgl/renderer/buckets/hillshade_bucket.cpp
+++ b/src/mbgl/renderer/buckets/hillshade_bucket.cpp
@@ -8,7 +8,7 @@ namespace mbgl {
 
 using namespace style;
 
-HillshadeBucket::HillshadeBucket(PremultipliedImage&& image_): demdata(image_) {
+HillshadeBucket::HillshadeBucket(PremultipliedImage&& image_, Tileset::DEMEncoding encoding): demdata(image_, encoding) {
 }
 
 HillshadeBucket::HillshadeBucket(DEMData&& demdata_) : demdata(std::move(demdata_)) {
diff --git a/src/mbgl/renderer/buckets/hillshade_bucket.hpp b/src/mbgl/renderer/buckets/hillshade_bucket.hpp
index 3d9f6c61af..5335f7ceda 100644
--- a/src/mbgl/renderer/buckets/hillshade_bucket.hpp
+++ b/src/mbgl/renderer/buckets/hillshade_bucket.hpp
@@ -8,6 +8,7 @@
 #include <mbgl/renderer/bucket.hpp>
 #include <mbgl/renderer/tile_mask.hpp>
 #include <mbgl/geometry/dem_data.hpp>
+#include <mbgl/util/tileset.hpp>
 #include <mbgl/util/image.hpp>
 #include <mbgl/util/mat4.hpp>
 #include <mbgl/util/optional.hpp>
@@ -16,8 +17,8 @@ namespace mbgl {
 
 class HillshadeBucket : public Bucket {
 public:
-    HillshadeBucket(PremultipliedImage&&);
-    HillshadeBucket(std::shared_ptr<PremultipliedImage>);
+    HillshadeBucket(PremultipliedImage&&, Tileset::DEMEncoding encoding);
+    HillshadeBucket(std::shared_ptr<PremultipliedImage>, Tileset::DEMEncoding encoding);
     HillshadeBucket(DEMData&&);
 
 
diff --git a/src/mbgl/style/conversion/tileset.cpp b/src/mbgl/style/conversion/tileset.cpp
index 88e78b1a83..6d89cef944 100644
--- a/src/mbgl/style/conversion/tileset.cpp
+++ b/src/mbgl/style/conversion/tileset.cpp
@@ -40,6 +40,16 @@ optional<Tileset> Converter<Tileset>::operator()(const Convertible& value, Error
         }
     }
 
+    auto encodingValue = objectMember(value, "encoding");
+    if (encodingValue) {
+        optional<std::string> encoding = toString(*encodingValue);
+        if (encoding && *encoding == "terrarium") {
+            result.encoding = Tileset::DEMEncoding::Terrarium;
+        } else if (encoding && *encoding != "mapbox") {
+            error = { "invalid raster-dem encoding type - valid types are 'mapbox' and 'terrarium' " };
+        }
+    }
+
     auto minzoomValue = objectMember(value, "minzoom");
     if (minzoomValue) {
         optional<float> minzoom = toNumber(*minzoomValue);
diff --git a/src/mbgl/tile/raster_dem_tile.cpp b/src/mbgl/tile/raster_dem_tile.cpp
index b270378ece..5db298cf4c 100644
--- a/src/mbgl/tile/raster_dem_tile.cpp
+++ b/src/mbgl/tile/raster_dem_tile.cpp
@@ -21,6 +21,7 @@ RasterDEMTile::RasterDEMTile(const OverscaledTileID& id_,
       worker(parameters.workerScheduler,
              ActorRef<RasterDEMTile>(*this, mailbox)) {
 
+    encoding = tileset.encoding;
     if ( id.canonical.y == 0 ){
         // this tile doesn't have upper neighboring tiles so marked those as backfilled
         neighboringTiles = neighboringTiles | DEMTileNeighbors::NoUpper;
@@ -47,7 +48,7 @@ void RasterDEMTile::setMetadata(optional<Timestamp> modified_, optional<Timestam
 void RasterDEMTile::setData(std::shared_ptr<const std::string> data) {
     pending = true;
     ++correlationID;
-    worker.invoke(&RasterDEMTileWorker::parse, data, correlationID);
+    worker.invoke(&RasterDEMTileWorker::parse, data, correlationID, encoding);
 }
 
 void RasterDEMTile::onParsed(std::unique_ptr<HillshadeBucket> result, const uint64_t resultCorrelationID) {
diff --git a/src/mbgl/tile/raster_dem_tile.hpp b/src/mbgl/tile/raster_dem_tile.hpp
index 68f8a91e00..0c8dd75961 100644
--- a/src/mbgl/tile/raster_dem_tile.hpp
+++ b/src/mbgl/tile/raster_dem_tile.hpp
@@ -94,6 +94,7 @@ private:
     Actor<RasterDEMTileWorker> worker;
     
     uint64_t correlationID = 0;
+    Tileset::DEMEncoding encoding;
 
     // Contains the Bucket object for the tile. Buckets are render
     // objects and they get added by tile parsing operations.
diff --git a/src/mbgl/tile/raster_dem_tile_worker.cpp b/src/mbgl/tile/raster_dem_tile_worker.cpp
index ed8573788f..7338e578c7 100644
--- a/src/mbgl/tile/raster_dem_tile_worker.cpp
+++ b/src/mbgl/tile/raster_dem_tile_worker.cpp
@@ -10,14 +10,14 @@ RasterDEMTileWorker::RasterDEMTileWorker(ActorRef<RasterDEMTileWorker>, ActorRef
     : parent(std::move(parent_)) {
 }
 
-void RasterDEMTileWorker::parse(std::shared_ptr<const std::string> data, uint64_t correlationID) {
+void RasterDEMTileWorker::parse(std::shared_ptr<const std::string> data, uint64_t correlationID, Tileset::DEMEncoding encoding) {
     if (!data) {
         parent.invoke(&RasterDEMTile::onParsed, nullptr, correlationID); // No data; empty tile.
         return;
     }
 
     try {
-        auto bucket = std::make_unique<HillshadeBucket>(decodeImage(*data));
+        auto bucket = std::make_unique<HillshadeBucket>(decodeImage(*data), encoding);
         parent.invoke(&RasterDEMTile::onParsed, std::move(bucket), correlationID);
     } catch (...) {
         parent.invoke(&RasterDEMTile::onError, std::current_exception(), correlationID);
diff --git a/src/mbgl/tile/raster_dem_tile_worker.hpp b/src/mbgl/tile/raster_dem_tile_worker.hpp
index 14fd1f43b5..5a8222bc2d 100644
--- a/src/mbgl/tile/raster_dem_tile_worker.hpp
+++ b/src/mbgl/tile/raster_dem_tile_worker.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <mbgl/actor/actor_ref.hpp>
+#include <mbgl/util/tileset.hpp>
 
 #include <memory>
 #include <string>
@@ -13,7 +14,7 @@ class RasterDEMTileWorker {
 public:
     RasterDEMTileWorker(ActorRef<RasterDEMTileWorker>, ActorRef<RasterDEMTile>);
 
-    void parse(std::shared_ptr<const std::string> data, uint64_t correlationID);
+    void parse(std::shared_ptr<const std::string> data, uint64_t correlationID, Tileset::DEMEncoding encoding);
 
 private:
     ActorRef<RasterDEMTile> parent;