Custom drawable layer: Simple Fill (#1810)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Alex Cristici <alex.cristici@gmail.com>

include/mbgl/gfx/drawable_builder.hpp

@@ -204,6 +204,8 @@ public:
     /// return the curent vertex count
     std::size_t curVertexCount() const;
 
+    bool empty() const { return !(drawables.size() || curVertexCount()); }
+
 protected:
     /// Create an instance of the appropriate drawable type
     virtual UniqueDrawable createDrawable() const = 0;

include/mbgl/gfx/fill_generator.hpp

@@ -0,0 +1,25 @@
+#pragma once
+
+#include <mbgl/util/geometry.hpp>
+#include <mbgl/tile/geometry_tile_data.hpp>
+#include <mbgl/gfx/vertex_vector.hpp>
+#include <mbgl/gfx/index_vector.hpp>
+#include <mbgl/programs/fill_program.hpp>
+
+namespace mbgl {
+namespace gfx {
+
+void generateFillBuffers(const GeometryCollection& geometry,
+                         gfx::VertexVector<FillLayoutVertex>& vertices,
+                         SegmentVector<FillAttributes>& triangleSegments,
+                         gfx::IndexVector<Triangles>& triangles);
+
+void generateFillAndOutineBuffers(const GeometryCollection& geometry,
+                                  gfx::VertexVector<FillLayoutVertex>& vertices,
+                                  SegmentVector<FillAttributes>& lineSegments,
+                                  gfx::IndexVector<gfx::Lines>& lines,
+                                  SegmentVector<FillAttributes>& triangleSegments,
+                                  gfx::IndexVector<gfx::Triangles>& triangles);
+
+} // namespace gfx
+} // namespace mbgl

include/mbgl/style/layers/custom_drawable_layer.hpp

@@ -41,6 +41,11 @@ public:
         gfx::PolylineGeneratorOptions geometry;
     };
 
+    struct FillOptions {
+        Color color;
+        float opacity = 1.f;
+    };
+
 public:
     /// @brief Construct a new Interface object (internal core use only)
     Interface(RenderLayer& layer,
@@ -72,6 +77,13 @@ public:
      */
     void setLineOptions(const LineOptions& options);
 
+    /**
+     * @brief Set the fill options
+     *
+     * @param options
+     */
+    void setFillOptions(const FillOptions& options);
+
     /**
      * @brief Add a polyline
      *
@@ -80,17 +92,14 @@ public:
      */
     void addPolyline(const GeometryCoordinates& coordinates);
 
+    void addFill(const GeometryCollection& geometry);
+
     /**
-     * @brief Finishe the current drawable building session
+     * @brief Finish the current drawable building session
      *
      */
     void finish();
 
-protected:
-    gfx::ShaderPtr lineShaderDefault() const;
-
-    std::unique_ptr<gfx::DrawableBuilder> createBuilder(const std::string& name, gfx::ShaderPtr shader) const;
-
 public:
     RenderLayer& layer;
     LayerGroupBasePtr& layerGroup;
@@ -102,9 +111,17 @@ public:
     UniqueChangeRequestVec& changes;
 
 private:
+    gfx::ShaderPtr lineShaderDefault() const;
+    gfx::ShaderPtr fillShaderDefault() const;
+
+    std::unique_ptr<gfx::DrawableBuilder> createBuilder(const std::string& name, gfx::ShaderPtr shader) const;
+
+    gfx::ShaderPtr lineShader;
+    gfx::ShaderPtr fillShader;
     std::unique_ptr<gfx::DrawableBuilder> builder;
     std::optional<OverscaledTileID> tileID;
     LineOptions lineOptions;
+    FillOptions fillOptions;
 };
 
 class CustomDrawableLayer final : public Layer {