Use a host interface for CustomLayer instead of function pointers (#11553)

Use a host interface for CustomLayer instead of function pointers

Co-authored-by: Julian Rex <julian.rex@mapbox.com>

2 files changed, 43 insertions, 49 deletions

diff --git a/include/mbgl/renderer/renderer_backend.hpp b/include/mbgl/renderer/renderer_backend.hpp
index b83c128169..1d5f4e8f4e 100644
--- a/include/mbgl/renderer/renderer_backend.hpp
+++ b/include/mbgl/renderer/renderer_backend.hpp
@@ -47,10 +47,10 @@ protected:
     // as a matched pair, exclusively through BackendScope, in two situations:
     //
     //   1. When releasing GL resources during Renderer destruction
-    //      (Including calling CustomLayerDeinitializeFunction during RenderCustomLayer destruction)
+    //      (Including calling CustomLayerHost::deinitialize during RenderCustomLayer destruction)
     //   2. When renderering through Renderer::render()
-    //      (Including calling CustomLayerDeinitializeFunction for newly added custom layers and
-    //       CustomLayerDeinitializeFunction on layer removal)
+    //      (Including calling CustomLayerHost::initialize for newly added custom layers and
+    //       CustomLayerHost::deinitialize on layer removal)
     virtual void activate() = 0;
     virtual void deactivate() = 0;
 
diff --git a/include/mbgl/style/layers/custom_layer.hpp b/include/mbgl/style/layers/custom_layer.hpp
index bf3387f95b..9911df9a1e 100644
--- a/include/mbgl/style/layers/custom_layer.hpp
+++ b/include/mbgl/style/layers/custom_layer.hpp
@@ -6,16 +6,7 @@ namespace mbgl {
 namespace style {
 
 /**
- * Initialize any GL state needed by the custom layer. This method is called once, from the
- * main thread, at a point when the GL context is active but before rendering for the first
- * time.
- *
- * Resources that are acquired in this method must be released in the UninitializeFunction.
- */
-using CustomLayerInitializeFunction = void (*)(void* context);
-
-/**
- * Parameters that define the current camera position for a CustomLayerRenderFunction.
+ * Parameters that define the current camera position for a `CustomLayerHost::render()` function.
  */
 struct CustomLayerRenderParameters {
     double width;
@@ -28,46 +19,49 @@ struct CustomLayerRenderParameters {
     double fieldOfView;
 };
 
-/**
- * Render the layer. This method is called once per frame. The implementation should not make
- * any assumptions about the GL state (other than that the correct context is active). It may
- * make changes to the state, and is not required to reset values such as the depth mask, stencil
- * mask, and corresponding test flags to their original values.
- * Make sure that you are drawing your fragments with a z value of 1 to take advantage of the
- * opaque fragment culling in case there are opaque layers above your custom layer.
- */
-using CustomLayerRenderFunction = void (*)(void* context, const CustomLayerRenderParameters&);
-
-/**
- * Called when the system has destroyed the underlying GL context. The
- * `CustomLayerDeinitializeFunction` will not be called in this case, however
- * `CustomLayerInitializeFunction` will be called instead to prepare for a new render.
- *
- */
-using CustomLayerContextLostFunction = void (*)(void* context);
-
-/**
- * Destroy any GL state needed by the custom layer, and deallocate context, if necessary. This
- * method is called once, from the main thread, at a point when the GL context is active.
- *
- * Note that it may be called even when the InitializeFunction has not been called.
- */
-using CustomLayerDeinitializeFunction = void (*)(void* context);
+class CustomLayerHost {
+public:
+    virtual ~CustomLayerHost() = default;
+    /**
+     * Initialize any GL state needed by the custom layer. This method is called once, from the
+     * main thread, at a point when the GL context is active but before rendering for the first
+     * time.
+     *
+     * Resources that are acquired in this method must be released in the `deinitialize` function.
+     */
+    virtual void initialize() = 0;
+
+    /**
+     * Render the layer. This method is called once per frame. The implementation should not make
+     * any assumptions about the GL state (other than that the correct context is active). It may
+     * make changes to the state, and is not required to reset values such as the depth mask, stencil
+     * mask, and corresponding test flags to their original values.
+     * Make sure that you are drawing your fragments with a z value of 1 to take advantage of the
+     * opaque fragment culling in case there are opaque layers above your custom layer.
+     */
+    virtual void render(const CustomLayerRenderParameters&) = 0;
+
+    /**
+     * Called when the system has destroyed the underlying GL context. The
+     * `deinitialize` function will not be called in this case, however
+     * `initialize` will be called instead to prepare for a new render.
+     *
+     */
+    virtual void contextLost() = 0;
+
+    /**
+     * Destroy any GL state needed by the custom layer, and deallocate context, if necessary. This
+     * method is called once, from the main thread, at a point when the GL context is active.
+     *
+     * Note that it may be called even when the `initialize` function has not been called.
+     */
+    virtual void deinitialize() = 0;
+};
 
 class CustomLayer : public Layer {
 public:
     CustomLayer(const std::string& id,
-                CustomLayerInitializeFunction,
-                CustomLayerRenderFunction,
-                CustomLayerContextLostFunction,
-                CustomLayerDeinitializeFunction,
-                void* context);
-
-    CustomLayer(const std::string& id,
-                CustomLayerInitializeFunction,
-                CustomLayerRenderFunction,
-                CustomLayerDeinitializeFunction,
-                void* context);
+                std::unique_ptr<CustomLayerHost> host);
 
     ~CustomLayer() final;