[core] Refactor CustomLayer internals

Move the responsibility for initialization/deinitialization/rendering to RenderCustomLayer. This eliminates special case code from Map and Style.

src/mbgl/map/map.cpp

@@ -904,20 +904,14 @@ Layer* Map::getLayer(const std::string& layerID) {
 
 void Map::addLayer(std::unique_ptr<Layer> layer, const optional<std::string>& before) {
     impl->styleMutated = true;
-    BackendScope guard(impl->backend);
-
     impl->style->addLayer(std::move(layer), before);
     impl->onUpdate(Update::Repaint);
 }
 
 std::unique_ptr<Layer> Map::removeLayer(const std::string& id) {
     impl->styleMutated = true;
-    BackendScope guard(impl->backend);
-
-    auto removedLayer = impl->style->removeLayer(id);
     impl->onUpdate(Update::Repaint);
-
-    return removedLayer;
+    return impl->style->removeLayer(id);
 }
 
 void Map::addImage(std::unique_ptr<style::Image> image) {

src/mbgl/renderer/layers/render_custom_layer.cpp

@@ -1,15 +1,27 @@
 #include <mbgl/renderer/layers/render_custom_layer.hpp>
+#include <mbgl/renderer/painter.hpp>
+#include <mbgl/renderer/paint_parameters.hpp>
 #include <mbgl/style/layers/custom_layer_impl.hpp>
-#include <mbgl/renderer/bucket.hpp>
+#include <mbgl/map/transform_state.hpp>
+#include <mbgl/map/backend_scope.hpp>
 
 namespace mbgl {
 
+using namespace style;
+
 RenderCustomLayer::RenderCustomLayer(Immutable<style::CustomLayer::Impl> _impl)
-    : RenderLayer(style::LayerType::Custom, _impl) {
+    : RenderLayer(LayerType::Custom, _impl) {
 }
 
-const style::CustomLayer::Impl& RenderCustomLayer::impl() const {
-    return static_cast<const style::CustomLayer::Impl&>(*baseImpl);
+RenderCustomLayer::~RenderCustomLayer() {
+    assert(BackendScope::exists());
+    if (initialized && impl().deinitializeFn) {
+        impl().deinitializeFn(impl().context);
+    }
+}
+
+const CustomLayer::Impl& RenderCustomLayer::impl() const {
+    return static_cast<const CustomLayer::Impl&>(*baseImpl);
 }
 
 void RenderCustomLayer::evaluate(const PropertyEvaluationParameters&) {
@@ -24,5 +36,41 @@ std::unique_ptr<Bucket> RenderCustomLayer::createBucket(const BucketParameters&,
     assert(false);
     return nullptr;
 }
-    
+
+void RenderCustomLayer::render(Painter& painter, PaintParameters& paintParameters, RenderSource*) {
+    if (!initialized) {
+        assert(impl().initializeFn);
+        impl().initializeFn(impl().context);
+        initialized = true;
+    }
+
+    gl::Context& context = painter.context;
+    const TransformState& state = painter.state;
+
+    // Reset GL state to a known state so the CustomLayer always has a clean slate.
+    context.vertexArrayObject = 0;
+    context.setDepthMode(painter.depthModeForSublayer(0, gl::DepthMode::ReadOnly));
+    context.setStencilMode(gl::StencilMode::disabled());
+    context.setColorMode(painter.colorModeForRenderPass());
+
+    CustomLayerRenderParameters parameters;
+
+    parameters.width = state.getSize().width;
+    parameters.height = state.getSize().height;
+    parameters.latitude = state.getLatLng().latitude();
+    parameters.longitude = state.getLatLng().longitude();
+    parameters.zoom = state.getZoom();
+    parameters.bearing = -state.getAngle() * util::RAD2DEG;
+    parameters.pitch = state.getPitch();
+    parameters.fieldOfView = state.getFieldOfView();
+
+    assert(impl().renderFn);
+    impl().renderFn(impl().context, parameters);
+
+    // Reset the view back to our original one, just in case the CustomLayer changed
+    // the viewport or Framebuffer.
+    paintParameters.view.bind();
+    context.setDirtyState();
+}
+
 } // namespace mbgl

src/mbgl/renderer/layers/render_custom_layer.hpp

@@ -8,15 +8,19 @@ namespace mbgl {
 class RenderCustomLayer: public RenderLayer {
 public:
     RenderCustomLayer(Immutable<style::CustomLayer::Impl>);
-    ~RenderCustomLayer() final = default;
+    ~RenderCustomLayer() final;
 
     void transition(const TransitionParameters&) final {}
     void evaluate(const PropertyEvaluationParameters&) override;
     bool hasTransition() const override;
 
     std::unique_ptr<Bucket> createBucket(const BucketParameters&, const std::vector<const RenderLayer*>&) const final;
+    void render(Painter&, PaintParameters&, RenderSource*) final;
 
     const style::CustomLayer::Impl& impl() const;
+
+private:
+    bool initialized = false;
 };
 
 template <>

src/mbgl/renderer/painter.cpp

@@ -292,21 +292,6 @@ void Painter::renderPass(PaintParameters& parameters,
         if (layer.is<RenderBackgroundLayer>()) {
             MBGL_DEBUG_GROUP(context, "background");
             renderBackground(parameters, *layer.as<RenderBackgroundLayer>());
-        } else if (layer.is<RenderCustomLayer>()) {
-            MBGL_DEBUG_GROUP(context, layer.baseImpl->id + " - custom");
-
-            // Reset GL state to a known state so the CustomLayer always has a clean slate.
-            context.vertexArrayObject = 0;
-            context.setDepthMode(depthModeForSublayer(0, gl::DepthMode::ReadOnly));
-            context.setStencilMode(gl::StencilMode::disabled());
-            context.setColorMode(colorModeForRenderPass());
-
-            layer.as<RenderCustomLayer>()->impl().render(state);
-
-            // Reset the view back to our original one, just in case the CustomLayer changed
-            // the viewport or Framebuffer.
-            parameters.view.bind();
-            context.setDirtyState();
         } else if (layer.is<RenderFillExtrusionLayer>()) {
             const auto size = context.viewport.getCurrentValue().size;
 

src/mbgl/renderer/render_layer.hpp

@@ -19,10 +19,6 @@ class PaintParameters;
 class RenderSource;
 class RenderTile;
 
-namespace gl {
-class Context;
-}   // namespace gl
-
 class RenderLayer {
 protected:
     RenderLayer(style::LayerType, Immutable<style::Layer::Impl>);

src/mbgl/renderer/render_style.cpp

@@ -23,6 +23,7 @@
 #include <mbgl/sprite/sprite_loader.hpp>
 #include <mbgl/text/glyph_manager.hpp>
 #include <mbgl/geometry/line_atlas.hpp>
+#include <mbgl/map/backend_scope.hpp>
 #include <mbgl/map/query.hpp>
 #include <mbgl/tile/tile.hpp>
 #include <mbgl/util/math.hpp>
@@ -48,7 +49,9 @@ RenderStyle::RenderStyle(Scheduler& scheduler_, FileSource& fileSource_)
     glyphManager->setObserver(this);
 }
 
-RenderStyle::~RenderStyle() = default;
+RenderStyle::~RenderStyle() {
+    assert(BackendScope::exists()); // Required for custom layers.
+}
 
 void RenderStyle::setObserver(RenderStyleObserver* observer_) {
     observer = observer_;
@@ -78,6 +81,8 @@ const RenderLight& RenderStyle::getRenderLight() const {
 }
 
 void RenderStyle::update(const UpdateParameters& parameters) {
+    assert(BackendScope::exists()); // Required for custom layers.
+
     const bool zoomChanged = zoomHistory.update(parameters.transformState.getZoom(), parameters.timePoint);
 
     const TransitionParameters transitionParameters {

src/mbgl/style/layers/custom_layer_impl.cpp

@@ -1,5 +1,4 @@
 #include <mbgl/style/layers/custom_layer_impl.hpp>
-#include <mbgl/map/transform_state.hpp>
 
 namespace mbgl {
 namespace style {
@@ -23,33 +22,5 @@ bool CustomLayer::Impl::hasLayoutDifference(const Layer::Impl&) const {
 void CustomLayer::Impl::stringifyLayout(rapidjson::Writer<rapidjson::StringBuffer>&) const {
 }
 
-void CustomLayer::Impl::initialize() const {
-    assert(initializeFn);
-    initializeFn(context);
-}
-
-void CustomLayer::Impl::deinitialize() const {
-    if (deinitializeFn) {
-        deinitializeFn(context);
-    }
-}
-
-void CustomLayer::Impl::render(const TransformState& state) const {
-    assert(renderFn);
-
-    CustomLayerRenderParameters parameters;
-
-    parameters.width = state.getSize().width;
-    parameters.height = state.getSize().height;
-    parameters.latitude = state.getLatLng().latitude();
-    parameters.longitude = state.getLatLng().longitude();
-    parameters.zoom = state.getZoom();
-    parameters.bearing = -state.getAngle() * util::RAD2DEG;
-    parameters.pitch = state.getPitch();
-    parameters.fieldOfView = state.getFieldOfView();
-
-    renderFn(context, parameters);
-}
-
 } // namespace style
 } // namespace mbgl

src/mbgl/style/layers/custom_layer_impl.hpp

@@ -17,11 +17,6 @@ public:
          CustomLayerDeinitializeFunction,
          void* context);
 
-    void initialize() const;
-    void deinitialize() const;
-    void render(const TransformState&) const;
-
-private:
     bool hasLayoutDifference(const Layer::Impl&) const override;
     void stringifyLayout(rapidjson::Writer<rapidjson::StringBuffer>&) const override;
 

src/mbgl/style/style.cpp

@@ -2,11 +2,8 @@
 #include <mbgl/style/observer.hpp>
 #include <mbgl/style/source_impl.hpp>
 #include <mbgl/style/layers/symbol_layer.hpp>
-#include <mbgl/style/layers/symbol_layer_impl.hpp>
 #include <mbgl/style/layers/custom_layer.hpp>
-#include <mbgl/style/layers/custom_layer_impl.hpp>
 #include <mbgl/style/layers/background_layer.hpp>
-#include <mbgl/style/layers/background_layer_impl.hpp>
 #include <mbgl/style/layers/fill_layer.hpp>
 #include <mbgl/style/layers/fill_extrusion_layer.hpp>
 #include <mbgl/style/layers/line_layer.hpp>
@@ -35,13 +32,7 @@ Style::Style(Scheduler& scheduler_, FileSource& fileSource_, float pixelRatio)
     light->setObserver(this);
 }
 
-Style::~Style() {
-    for (const auto& layer : layers) {
-        if (auto* customLayer = layer->as<CustomLayer>()) {
-            customLayer->impl().deinitialize();
-        }
-    }
-}
+Style::~Style() = default;
 
 void Style::setTransitionOptions(const TransitionOptions& options) {
     transitionOptions = options;
@@ -153,10 +144,6 @@ Layer* Style::addLayer(std::unique_ptr<Layer> layer, optional<std::string> befor
         throw std::runtime_error(std::string{"Layer "} + layer->getID() + " already exists");
     }
 
-    if (auto* customLayer = layer->as<CustomLayer>()) {
-        customLayer->impl().initialize();
-    }
-
     layer->setObserver(this);
 
     return layers.add(std::move(layer), before);
@@ -167,10 +154,6 @@ std::unique_ptr<Layer> Style::removeLayer(const std::string& id) {
 
     if (layer) {
         layer->setObserver(nullptr);
-
-        if (auto* customLayer = layer->as<CustomLayer>()) {
-            customLayer->impl().deinitialize();
-        }
     }
 
     return layer;

test/tile/annotation_tile.test.cpp

@@ -14,6 +14,8 @@
 #include <mbgl/annotation/annotation_tile.hpp>
 #include <mbgl/renderer/image_manager.hpp>
 #include <mbgl/text/glyph_manager.hpp>
+#include <mbgl/map/backend_scope.hpp>
+#include <mbgl/gl/headless_backend.hpp>
 
 #include <memory>
 
@@ -26,6 +28,8 @@ public:
     util::RunLoop loop;
     ThreadPool threadPool { 1 };
     AnnotationManager annotationManager;
+    HeadlessBackend backend { test::sharedDisplay() };
+    BackendScope scope { backend };
     RenderStyle style { threadPool, fileSource };
     ImageManager imageManager;
     GlyphManager glyphManager { fileSource };