From ea51b11dccdc117c7dc43ffd3b3d0f969f59799f Mon Sep 17 00:00:00 2001
From: Bruno de Oliveira Abinader <bruno@mapbox.com>
Date: Wed, 17 Oct 2018 13:38:11 +0200
Subject: [core] Introduce mbgl::RendererState

---
 cmake/core-files.txt                           |  2 ++
 include/mbgl/renderer/renderer_state.hpp       | 22 ++++++++++++++++++++
 platform/default/mbgl/gl/headless_frontend.cpp |  1 +
 src/mbgl/map/transform_state.hpp               |  1 +
 src/mbgl/renderer/renderer_state.cpp           | 10 +++++++++
 test/map/map.test.cpp                          | 28 ++++++++++++++++++++++++++
 6 files changed, 64 insertions(+)
 create mode 100644 include/mbgl/renderer/renderer_state.hpp
 create mode 100644 src/mbgl/renderer/renderer_state.cpp

diff --git a/cmake/core-files.txt b/cmake/core-files.txt
index 1d7d2ef41f..7c52e08ccf 100644
--- a/cmake/core-files.txt
+++ b/cmake/core-files.txt
@@ -180,6 +180,7 @@ include/mbgl/renderer/renderer.hpp
 include/mbgl/renderer/renderer_backend.hpp
 include/mbgl/renderer/renderer_frontend.hpp
 include/mbgl/renderer/renderer_observer.hpp
+include/mbgl/renderer/renderer_state.hpp
 src/mbgl/renderer/backend_scope.cpp
 src/mbgl/renderer/bucket.hpp
 src/mbgl/renderer/bucket_parameters.cpp
@@ -216,6 +217,7 @@ src/mbgl/renderer/renderer.cpp
 src/mbgl/renderer/renderer_backend.cpp
 src/mbgl/renderer/renderer_impl.cpp
 src/mbgl/renderer/renderer_impl.hpp
+src/mbgl/renderer/renderer_state.cpp
 src/mbgl/renderer/style_diff.cpp
 src/mbgl/renderer/style_diff.hpp
 src/mbgl/renderer/tile_mask.hpp
diff --git a/include/mbgl/renderer/renderer_state.hpp b/include/mbgl/renderer/renderer_state.hpp
new file mode 100644
index 0000000000..1b300c190b
--- /dev/null
+++ b/include/mbgl/renderer/renderer_state.hpp
@@ -0,0 +1,22 @@
+#pragma once
+
+#include <mbgl/map/camera.hpp>
+#include <mbgl/util/geo.hpp>
+
+namespace mbgl {
+
+class UpdateParameters;
+
+/**
+ * RendererState acts as a Memento-like object that is able to extract data out of UpdateParameters (an opaque object
+ * from the public API perspective).
+ */
+class RendererState {
+public:
+
+    // Obtains a CameraOptions out of a given UpdateParameters object.
+    static CameraOptions getCameraOptions(UpdateParameters&, const EdgeInsets& = {});
+
+};
+
+} // namespace mbgl
diff --git a/platform/default/mbgl/gl/headless_frontend.cpp b/platform/default/mbgl/gl/headless_frontend.cpp
index c87a2796c9..1ec11a195f 100644
--- a/platform/default/mbgl/gl/headless_frontend.cpp
+++ b/platform/default/mbgl/gl/headless_frontend.cpp
@@ -1,5 +1,6 @@
 #include <mbgl/gl/headless_frontend.hpp>
 #include <mbgl/renderer/renderer.hpp>
+#include <mbgl/renderer/renderer_state.hpp>
 #include <mbgl/renderer/update_parameters.hpp>
 #include <mbgl/map/map.hpp>
 #include <mbgl/map/transform_state.hpp>
diff --git a/src/mbgl/map/transform_state.hpp b/src/mbgl/map/transform_state.hpp
index 4049965618..fe716d8ea8 100644
--- a/src/mbgl/map/transform_state.hpp
+++ b/src/mbgl/map/transform_state.hpp
@@ -20,6 +20,7 @@ class UnwrappedTileID;
 
 class TransformState {
     friend class Transform;
+    friend class RendererState;
 
 public:
     TransformState(ConstrainMode = ConstrainMode::HeightOnly, ViewportMode = ViewportMode::Default);
diff --git a/src/mbgl/renderer/renderer_state.cpp b/src/mbgl/renderer/renderer_state.cpp
new file mode 100644
index 0000000000..dc5c4c1292
--- /dev/null
+++ b/src/mbgl/renderer/renderer_state.cpp
@@ -0,0 +1,10 @@
+#include <mbgl/renderer/renderer_state.hpp>
+#include <mbgl/renderer/update_parameters.hpp>
+
+namespace mbgl {
+
+CameraOptions RendererState::getCameraOptions(UpdateParameters& updateParameters, const EdgeInsets& padding) {
+    return updateParameters.transformState.getCameraOptions(padding);
+}
+
+} // namespace mbgl
diff --git a/test/map/map.test.cpp b/test/map/map.test.cpp
index 88ddfa6cee..cd15c5c278 100644
--- a/test/map/map.test.cpp
+++ b/test/map/map.test.cpp
@@ -49,6 +49,34 @@ public:
     }
 };
 
+TEST(Map, RendererState) {
+    MapTest<> test;
+
+    // Map hasn't notified the frontend about an update yet.
+    CameraOptions nullOptions;
+    ASSERT_EQ(test.frontend.getCameraOptions(), nullOptions);
+
+    LatLng coordinate { 1, 1 };
+    double zoom = 12.0;
+    double pitchInDegrees = 45.0;
+    double bearingInDegrees = 30.0;
+
+    test.map.getStyle().loadJSON(util::read_file("test/fixtures/api/empty.json"));
+    test.map.setLatLngZoom(coordinate, zoom);
+    test.map.setPitch(pitchInDegrees);
+    test.map.setBearing(bearingInDegrees);
+
+    test.runLoop.runOnce();
+    test.frontend.render(test.map);
+
+    const CameraOptions& options = test.frontend.getCameraOptions();
+    EXPECT_NEAR(options.center->latitude(), coordinate.latitude(), 1e-7);
+    EXPECT_NEAR(options.center->longitude(), coordinate.longitude(), 1e-7);
+    ASSERT_DOUBLE_EQ(*options.zoom, zoom);
+    ASSERT_DOUBLE_EQ(*options.pitch, pitchInDegrees);
+    EXPECT_NEAR(*options.angle, bearingInDegrees, 1e-7);
+}
+
 TEST(Map, LatLngBehavior) {
     MapTest<> test;
 
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