[core] Refactor CustomLayer internals

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

5 files changed, 64 insertions, 26 deletions

diff --git a/src/mbgl/renderer/layers/render_custom_layer.cpp b/src/mbgl/renderer/layers/render_custom_layer.cpp
index add3d0d5ad..4d6084075d 100644
--- a/src/mbgl/renderer/layers/render_custom_layer.cpp
+++ b/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) {
+}
+
+RenderCustomLayer::~RenderCustomLayer() {
+    assert(BackendScope::exists());
+    if (initialized && impl().deinitializeFn) {
+        impl().deinitializeFn(impl().context);
+    }
 }
 
-const style::CustomLayer::Impl& RenderCustomLayer::impl() const {
-    return static_cast<const style::CustomLayer::Impl&>(*baseImpl);
+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
diff --git a/src/mbgl/renderer/layers/render_custom_layer.hpp b/src/mbgl/renderer/layers/render_custom_layer.hpp
index 2f7c2d3239..dd52d315cf 100644
--- a/src/mbgl/renderer/layers/render_custom_layer.hpp
+++ b/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 <>
diff --git a/src/mbgl/renderer/painter.cpp b/src/mbgl/renderer/painter.cpp
index 5a70243a54..47db8254e2 100644
--- a/src/mbgl/renderer/painter.cpp
+++ b/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;
 
diff --git a/src/mbgl/renderer/render_layer.hpp b/src/mbgl/renderer/render_layer.hpp
index 50ad4c771a..e06f479281 100644
--- a/src/mbgl/renderer/render_layer.hpp
+++ b/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>);
diff --git a/src/mbgl/renderer/render_style.cpp b/src/mbgl/renderer/render_style.cpp
index 589a493621..f9c3f0ca9f 100644
--- a/src/mbgl/renderer/render_style.cpp
+++ b/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 {