[core] Add RendererState::{pixelForLatLng,latLngForPixel}

include/mbgl/renderer/renderer_state.hpp

@@ -15,16 +15,22 @@ class RendererState {
 public:
 
     // Obtains a CameraOptions out of a given UpdateParameters object.
-    static CameraOptions getCameraOptions(UpdateParameters&, const EdgeInsets& = {});
+    static CameraOptions getCameraOptions(const UpdateParameters&, const EdgeInsets& = {});
 
     // Returns whether an image with the given ID exists from a given UpdateParamters object.
-    static bool hasImage(UpdateParameters&, const std::string& id);
+    static bool hasImage(const UpdateParameters&, const std::string& id);
 
     // Returns whether a layer with the given ID exists from a given UpdateParamters object.
-    static bool hasLayer(UpdateParameters&, const std::string& id);
+    static bool hasLayer(const UpdateParameters&, const std::string& id);
 
     // Returns whether a source with the given ID exists from a given UpdateParamters object.
-    static bool hasSource(UpdateParameters&, const std::string& id);
+    static bool hasSource(const UpdateParameters&, const std::string& id);
+
+    // Obtains the geographical coordinate out of a given screen coordinate.
+    static ScreenCoordinate pixelForLatLng(const UpdateParameters&, const LatLng&);
+
+    // Obtains the screen coordinate out of a given geographical coordinate.
+    static LatLng latLngForPixel(const UpdateParameters&, const ScreenCoordinate&);
 };
 
 } // namespace mbgl

platform/default/mbgl/gl/headless_frontend.cpp

@@ -87,6 +87,21 @@ bool HeadlessFrontend::hasSource(const std::string& id) {
 
     return false;
 }
+ScreenCoordinate HeadlessFrontend::pixelForLatLng(const LatLng& coordinate) {
+    if (updateParameters) {
+        return RendererState::pixelForLatLng(*updateParameters, coordinate);
+    }
+
+    return ScreenCoordinate {};
+}
+
+LatLng HeadlessFrontend::latLngForPixel(const ScreenCoordinate& point) {
+    if (updateParameters) {
+        return RendererState::latLngForPixel(*updateParameters, point);
+    }
+
+    return LatLng {};
+}
 
 void HeadlessFrontend::setSize(Size size_) {
     if (size != size_) {

platform/default/mbgl/gl/headless_frontend.hpp

@@ -39,6 +39,9 @@ public:
     bool hasLayer(const std::string&);
     bool hasSource(const std::string&);
 
+    ScreenCoordinate pixelForLatLng(const LatLng&);
+    LatLng latLngForPixel(const ScreenCoordinate&);
+
     PremultipliedImage readStillImage();
     PremultipliedImage render(Map&);
 

src/mbgl/renderer/renderer_state.cpp

@@ -7,11 +7,11 @@
 
 namespace mbgl {
 
-CameraOptions RendererState::getCameraOptions(UpdateParameters& updateParameters, const EdgeInsets& padding) {
+CameraOptions RendererState::getCameraOptions(const UpdateParameters& updateParameters, const EdgeInsets& padding) {
     return updateParameters.transformState.getCameraOptions(padding);
 }
 
-bool RendererState::hasImage(UpdateParameters& updateParameters, const std::string& id) {
+bool RendererState::hasImage(const UpdateParameters& updateParameters, const std::string& id) {
     for (const auto& image : *updateParameters.images) {
         if (image.get()->id == id) {
             return true;
@@ -20,7 +20,7 @@ bool RendererState::hasImage(UpdateParameters& updateParameters, const std::stri
     return false;
 }
 
-bool RendererState::hasLayer(UpdateParameters& updateParameters, const std::string& id) {
+bool RendererState::hasLayer(const UpdateParameters& updateParameters, const std::string& id) {
     for (const auto& layer : *updateParameters.layers) {
         if (layer.get()->id == id) {
             return true;
@@ -29,7 +29,7 @@ bool RendererState::hasLayer(UpdateParameters& updateParameters, const std::stri
     return false;
 }
 
-bool RendererState::hasSource(UpdateParameters& updateParameters, const std::string& id) {
+bool RendererState::hasSource(const UpdateParameters& updateParameters, const std::string& id) {
     for (const auto& source : *updateParameters.sources) {
         if (source.get()->id == id) {
             return true;
@@ -38,5 +38,20 @@ bool RendererState::hasSource(UpdateParameters& updateParameters, const std::str
     return false;
 }
 
+ScreenCoordinate RendererState::pixelForLatLng(const UpdateParameters& updateParameters, const LatLng& latLng) {
+    // If the center and point longitudes are not in the same side of the
+    // antimeridian, we unwrap the point longitude so it would be seen if
+    // e.g. the next antimeridian side is visible.
+    LatLng unwrappedLatLng = latLng.wrapped();
+    unwrappedLatLng.unwrapForShortestPath(updateParameters.transformState.getLatLng());
+    const ScreenCoordinate point = updateParameters.transformState.latLngToScreenCoordinate(latLng);
+    return ScreenCoordinate { point.x, updateParameters.transformState.size.height - point.y };
+}
+
+LatLng RendererState::latLngForPixel(const UpdateParameters& updateParameters, const ScreenCoordinate& point) {
+    ScreenCoordinate flippedPoint = point;
+    flippedPoint.y = updateParameters.transformState.size.height - flippedPoint.y;
+    return updateParameters.transformState.screenCoordinateToLatLng(flippedPoint);
+}
 
 } // namespace mbgl

test/map/map.test.cpp

@@ -79,6 +79,16 @@ TEST(Map, RendererState) {
     ASSERT_DOUBLE_EQ(*options.pitch, pitchInDegrees);
     EXPECT_NEAR(*options.angle, bearingInDegrees, 1e-7);
 
+    {
+        const LatLng& latLng = test.frontend.latLngForPixel(ScreenCoordinate { 0, 0 });
+        const ScreenCoordinate& point = test.frontend.pixelForLatLng(coordinate);
+        EXPECT_NEAR(coordinate.latitude(), latLng.latitude(), 1e-1);
+        EXPECT_NEAR(coordinate.longitude(), latLng.longitude(), 1e-1);
+        const Size size = test.map.getSize();
+        EXPECT_NEAR(point.x, size.width / 2.0, 1e-7);
+        EXPECT_NEAR(point.y, size.height / 2.0, 1e-7);
+    }
+
     // RendererState::hasImage
     test.map.getStyle().addImage(std::make_unique<style::Image>("default_marker", decodeImage(util::read_file("test/fixtures/sprites/default_marker.png")), 1.0));