Replace rather than update Metal buffers (#1842)

include/mbgl/gfx/rendering_stats.hpp

@@ -10,16 +10,36 @@ struct RenderingStats {
     RenderingStats() = default;
     bool isZero() const;
 
+    /// Number of frames rendered
     int numFrames = 0;
+    /// Number of draw calls (`glDrawElements`, `drawIndexedPrimitives`, etc.) executed during the most recent frame
     int numDrawCalls = 0;
+    /// Total number of draw calls executed during all the frames
     int totalDrawCalls = 0;
 
+    /// Total number of textures created
     int numCreatedTextures = 0;
+    /// Net textures
     int numActiveTextures = 0;
+    /// Net texture bindings
     int numTextureBindings = 0;
+    /// Number of times a texture was updated
     int numTextureUpdates = 0;
+    /// Number of bytes used in texture updates
     std::size_t textureUpdateBytes = 0;
 
+    /// Number of buffers created
+    std::size_t totalBuffers = 0;
+    /// Number of SDK-specific buffers created
+    std::size_t totalBufferObjs = 0;
+    /// Number of times a buffer is updated
+    std::size_t bufferUpdates = 0;
+    /// Number of times an SDK-specific buffer is updated
+    std::size_t bufferObjUpdates = 0;
+    /// Sum of update sizes
+    std::size_t bufferUpdateBytes = 0;
+
+    /// Number of active buffers
     int numBuffers = 0;
     int numFrameBuffers = 0;
 

include/mbgl/mtl/context.hpp

@@ -66,9 +66,7 @@ public:
     MTLTexturePtr createMetalTexture(MTLTextureDescriptorPtr textureDescriptor) const;
     MTLSamplerStatePtr createMetalSamplerState(MTLSamplerDescriptorPtr samplerDescriptor) const;
 
-    void clear();
-
-    // Actually remove the objects we marked as abandoned with the above methods.
+    /// Called at the end of a frame.
     void performCleanup() override;
 
     void reduceMemoryUsage() override {}