Rendering statistics view (#3322)

Co-authored-by: Bart Louwers <bart@emeel.net>

include/mbgl/gfx/rendering_stats.hpp

@@ -2,14 +2,27 @@
 
 #include <cstddef>
 #include <string>
+#include <memory>
+#include <mbgl/util/color.hpp>
 
 namespace mbgl {
+
+namespace style {
+class Style;
+class SymbolLayer;
+} // namespace style
+
 namespace gfx {
 
 struct RenderingStats {
     RenderingStats() = default;
     bool isZero() const;
 
+    /// Frame CPU encoding time (milliseconds)
+    double encodingTime = 0.0;
+    /// Frame CPU rendering time (milliseconds)
+    double renderingTime = 0.0;
+
     /// Number of frames rendered
     int numFrames = 0;
     /// Number of draw calls (`glDrawElements`, `drawIndexedPrimitives`, etc.) executed during the most recent frame
@@ -41,25 +54,40 @@ struct RenderingStats {
 
     /// Number of active buffers
     int numBuffers = 0;
+    /// Number of active offscreen frame buffers
     int numFrameBuffers = 0;
 
+    /// Number of active index buffers
     int numIndexBuffers = 0;
+    /// Sum of index buffers update sizes
     std::size_t indexUpdateBytes = 0;
 
+    /// Number of active vertex buffers
     int numVertexBuffers = 0;
+    /// Sum of vertex buffers update sizes
     std::size_t vertexUpdateBytes = 0;
 
+    /// Number of active uniform buffers
     int numUniformBuffers = 0;
+    /// Number of times a uniform buffer is updated
     int numUniformUpdates = 0;
+    /// Sum of uniform buffers update sizes
     std::size_t uniformUpdateBytes = 0;
 
+    /// Total texture memory
     int memTextures = 0;
+    /// Total buffer memory
     int memBuffers = 0;
+    /// Total index buffer memory
     int memIndexBuffers = 0;
+    /// Total vertex buffer memory
     int memVertexBuffers = 0;
+    /// Total uniform buffer memory
     int memUniformBuffers = 0;
 
+    /// Number of stencil buffer clears
     int stencilClears = 0;
+    /// Number of stencil buffer updates
     int stencilUpdates = 0;
 
     RenderingStats& operator+=(const RenderingStats&);
@@ -69,5 +97,38 @@ struct RenderingStats {
 #endif
 };
 
+class RenderingStatsView final {
+public:
+    struct Options {
+        float updateInterval = 0.25f;
+        bool verbose = false;
+        Color textColor = Color::red();
+        float textSize = 4.0f;
+    };
+
+    RenderingStatsView() = default;
+    RenderingStatsView(const Options& options_)
+        : options(options_) {}
+    ~RenderingStatsView() = default;
+
+    void create(style::Style& style);
+    void destroy(style::Style& style);
+
+    mbgl::style::SymbolLayer* getLayer(style::Style& style);
+
+    void update(style::Style& style, const gfx::RenderingStats& stats);
+
+protected:
+    const std::string layerID = "rendering-stats";
+    const std::string sourceID = layerID + "-source";
+
+    Options options;
+
+    double lastUpdate = 0.0;
+    uint32_t frameCount = 0;
+    double encodingTime = 0.0;
+    double renderingTime = 0.0;
+};
+
 } // namespace gfx
 } // namespace mbgl