Add circle render type

As specified in:
https://github.com/mapbox/mapbox-gl-style-spec/blob/v8-circle/reference/v8.json

Part of #1740.

include/mbgl/style/style_properties.hpp

@@ -45,6 +45,20 @@ struct LineProperties {
     }
 };
 
+struct CircleProperties {
+    inline CircleProperties() {}
+    float radius = 5.0f;
+    Color color = {{ 0, 0, 0, 1 }};
+    float opacity = 1.0f;
+    std::array<float, 2> translate = {{ 0, 0 }};
+    TranslateAnchorType translateAnchor = TranslateAnchorType::Map;
+    float blur = 0;
+
+    inline bool isVisible() const {
+        return radius > 0 && color[3] > 0 && opacity > 0;
+    }
+};
+
 struct SymbolProperties {
     inline SymbolProperties() {}
 
@@ -100,6 +114,7 @@ struct BackgroundProperties {
 typedef mapbox::util::variant<
     FillProperties,
     LineProperties,
+    CircleProperties,
     SymbolProperties,
     RasterProperties,
     BackgroundProperties,

include/mbgl/style/types.hpp

@@ -27,6 +27,7 @@ enum class StyleLayerType : uint8_t {
     Unknown,
     Fill,
     Line,
+    Circle,
     Symbol,
     Raster,
     Background
@@ -36,6 +37,7 @@ MBGL_DEFINE_ENUM_CLASS(StyleLayerTypeClass, StyleLayerType, {
     { StyleLayerType::Unknown, "unknown" },
     { StyleLayerType::Fill, "fill" },
     { StyleLayerType::Line, "line" },
+    { StyleLayerType::Circle, "circle" },
     { StyleLayerType::Symbol, "symbol" },
     { StyleLayerType::Raster, "raster" },
     { StyleLayerType::Background, "background" },

src/mbgl/geometry/circle_buffer.cpp

@@ -0,0 +1,13 @@
+#include <mbgl/geometry/circle_buffer.hpp>
+
+#include <mbgl/platform/gl.hpp>
+
+#include <climits>
+
+using namespace mbgl;
+
+void CircleVertexBuffer::add(vertex_type x, vertex_type y, float ex, float ey) {
+    vertex_type *vertices = static_cast<vertex_type *>(addElement());
+    vertices[0] = (x * 2) + ((ex + 1) / 2);
+    vertices[1] = (y * 2) + ((ey + 1) / 2);
+}

src/mbgl/geometry/circle_buffer.hpp

@@ -0,0 +1,27 @@
+#ifndef MBGL_GEOMETRY_CIRCLE_BUFFER
+#define MBGL_GEOMETRY_CIRCLE_BUFFER
+
+#include <mbgl/geometry/buffer.hpp>
+
+namespace mbgl {
+
+class CircleVertexBuffer : public Buffer<
+    4 // 2 bytes per short * 4 of them.
+> {
+public:
+    typedef int16_t vertex_type;
+
+    /*
+     * Add a vertex to this buffer
+     *
+     * @param {number} x vertex position
+     * @param {number} y vertex position
+     * @param {number} ex extrude normal
+     * @param {number} ey extrude normal
+     */
+    void add(vertex_type x, vertex_type y, float ex, float ey);
+};
+
+}
+
+#endif // MBGL_GEOMETRY_CIRCLE_BUFFER

src/mbgl/map/tile_worker.cpp

@@ -5,6 +5,7 @@
 #include <mbgl/geometry/glyph_atlas.hpp>
 #include <mbgl/renderer/fill_bucket.hpp>
 #include <mbgl/renderer/line_bucket.hpp>
+#include <mbgl/renderer/circle_bucket.hpp>
 #include <mbgl/renderer/symbol_bucket.hpp>
 #include <mbgl/platform/log.hpp>
 #include <mbgl/util/constants.hpp>
@@ -139,15 +140,22 @@ void TileWorker::parseLayer(const StyleLayer& layer, const GeometryTile& geometr
 
     std::unique_ptr<Bucket> bucket;
 
-    if (styleBucket.type == StyleLayerType::Fill) {
+    switch (styleBucket.type) {
+    case StyleLayerType::Fill:
         bucket = createFillBucket(*geometryLayer, styleBucket);
-    } else if (styleBucket.type == StyleLayerType::Line) {
+        break;
+    case StyleLayerType::Line:
         bucket = createLineBucket(*geometryLayer, styleBucket);
-    } else if (styleBucket.type == StyleLayerType::Symbol) {
+        break;
+    case StyleLayerType::Circle:
+        bucket = createCircleBucket(*geometryLayer, styleBucket);
+        break;
+    case StyleLayerType::Symbol:
         bucket = createSymbolBucket(*geometryLayer, styleBucket);
-    } else if (styleBucket.type == StyleLayerType::Raster) {
+        break;
+    case StyleLayerType::Raster:
         return;
-    } else {
+    default:
         Log::Warning(Event::ParseTile, "unknown bucket render type for layer '%s' (source layer '%s')",
                 styleBucket.name.c_str(), styleBucket.source_layer.c_str());
     }
@@ -203,6 +211,17 @@ std::unique_ptr<Bucket> TileWorker::createLineBucket(const GeometryTileLayer& la
     return bucket->hasData() ? std::move(bucket) : nullptr;
 }
 
+std::unique_ptr<Bucket> TileWorker::createCircleBucket(const GeometryTileLayer& layer,
+                                                       const StyleBucket& bucket_desc) {
+    auto bucket = std::make_unique<CircleBucket>(circleVertexBuffer,
+                                                 triangleElementsBuffer);
+
+    // Circle does not have layout properties to apply.
+
+    addBucketGeometries(bucket, layer, bucket_desc.filter);
+    return bucket->hasData() ? std::move(bucket) : nullptr;
+}
+
 std::unique_ptr<Bucket> TileWorker::createSymbolBucket(const GeometryTileLayer& layer,
                                                        const StyleBucket& bucket_desc) {
     auto bucket = std::make_unique<SymbolBucket>(*collision, id.overscaling);

src/mbgl/map/tile_worker.hpp

@@ -6,6 +6,7 @@
 #include <mbgl/geometry/elements_buffer.hpp>
 #include <mbgl/geometry/fill_buffer.hpp>
 #include <mbgl/geometry/line_buffer.hpp>
+#include <mbgl/geometry/circle_buffer.hpp>
 #include <mbgl/util/noncopyable.hpp>
 #include <mbgl/util/ptr.hpp>
 #include <mbgl/style/filter_expression.hpp>
@@ -52,6 +53,7 @@ class TileWorker : public util::noncopyable {
 
     std::unique_ptr<Bucket> createFillBucket(const GeometryTileLayer&, const StyleBucket&);
     std::unique_ptr<Bucket> createLineBucket(const GeometryTileLayer&, const StyleBucket&);
+    std::unique_ptr<Bucket> createCircleBucket(const GeometryTileLayer&, const StyleBucket&);
     std::unique_ptr<Bucket> createSymbolBucket(const GeometryTileLayer&, const StyleBucket&);
 
     template <class Bucket>
@@ -68,6 +70,7 @@ class TileWorker : public util::noncopyable {
 
     FillVertexBuffer fillVertexBuffer;
     LineVertexBuffer lineVertexBuffer;
+    CircleVertexBuffer circleVertexBuffer;
 
     TriangleElementsBuffer triangleElementsBuffer;
     LineElementsBuffer lineElementsBuffer;

src/mbgl/renderer/circle_bucket.cpp

@@ -0,0 +1,92 @@
+#include <mbgl/renderer/circle_bucket.hpp>
+#include <mbgl/renderer/painter.hpp>
+
+#include <mbgl/shader/circle_shader.hpp>
+
+using namespace mbgl;
+
+CircleBucket::CircleBucket(CircleVertexBuffer& vertexBuffer,
+                           TriangleElementsBuffer& elementsBuffer)
+    : vertexBuffer_(vertexBuffer)
+    , elementsBuffer_(elementsBuffer)
+    , vertexStart_(vertexBuffer_.index())
+    , elementsStart_(elementsBuffer_.index()) {
+}
+
+CircleBucket::~CircleBucket() {
+    // Do not remove. header file only contains forward definitions to unique pointers.
+}
+
+void CircleBucket::upload() {
+    vertexBuffer_.upload();
+    elementsBuffer_.upload();
+    uploaded = true;
+}
+
+void CircleBucket::render(Painter& painter,
+                        const StyleLayer& layer_desc,
+                        const TileID& id,
+                        const mat4& matrix) {
+    painter.renderCircle(*this, layer_desc, id, matrix);
+}
+
+bool CircleBucket::hasData() const {
+    return !triangleGroups_.empty();
+}
+
+void CircleBucket::addGeometry(const GeometryCollection& geometryCollection) {
+    for (auto& circle : geometryCollection) {
+        for(auto & geometry : circle) {
+            auto x = geometry.x;
+            auto y = geometry.y;
+
+            // this geometry will be of the Point type, and we'll derive
+            // two triangles from it.
+            //
+            // ┌─────────┐
+            // │ 4     3 │
+            // │         │
+            // │ 1     2 │
+            // └─────────┘
+            //
+            vertexBuffer_.add(x, y, -1, -1); // 1
+            vertexBuffer_.add(x, y, 1, -1); // 2
+            vertexBuffer_.add(x, y, 1, 1); // 3
+            vertexBuffer_.add(x, y, -1, 1); // 4
+
+            if (!triangleGroups_.size() || (triangleGroups_.back()->vertex_length + 4 > 65535)) {
+                // Move to a new group because the old one can't hold the geometry.
+                triangleGroups_.emplace_back(std::make_unique<TriangleGroup>());
+            }
+
+            TriangleGroup& group = *triangleGroups_.back();
+            auto index = group.vertex_length;
+
+            // 1, 2, 3
+            // 1, 4, 3
+            elementsBuffer_.add(index, index + 1, index + 2);
+            elementsBuffer_.add(index, index + 3, index + 2);
+
+            group.vertex_length += 4;
+            group.elements_length += 2;
+        }
+    }
+}
+
+void CircleBucket::drawCircles(CircleShader& shader) {
+    char* vertexIndex = BUFFER_OFFSET(vertexStart_ * vertexBuffer_.itemSize);
+    char* elementsIndex = BUFFER_OFFSET(elementsStart_ * elementsBuffer_.itemSize);
+
+    for (auto& group : triangleGroups_) {
+        assert(group);
+
+        if (!group->elements_length) continue;
+
+        group->array[0].bind(shader, vertexBuffer_, elementsBuffer_, vertexIndex);
+
+        MBGL_CHECK_ERROR(glDrawElements(GL_TRIANGLES, group->elements_length * 3, GL_UNSIGNED_SHORT, elementsIndex));
+
+        vertexIndex += group->vertex_length * vertexBuffer_.itemSize;
+        elementsIndex += group->elements_length * elementsBuffer_.itemSize;
+    }
+}

src/mbgl/renderer/circle_bucket.hpp

@@ -0,0 +1,46 @@
+#ifndef MBGL_RENDERER_CIRCLE_BUCKET
+#define MBGL_RENDERER_CIRCLE_BUCKET
+
+#include <mbgl/renderer/bucket.hpp>
+
+#include <mbgl/map/geometry_tile.hpp>
+
+#include <mbgl/geometry/elements_buffer.hpp>
+#include <mbgl/geometry/circle_buffer.hpp>
+
+#include <mbgl/style/style_bucket.hpp>
+#include <mbgl/style/style_layout.hpp>
+
+namespace mbgl {
+
+class CircleVertexBuffer;
+class CircleShader;
+
+class CircleBucket : public Bucket {
+    using TriangleGroup = ElementGroup<3>;
+
+public:
+    CircleBucket(CircleVertexBuffer &vertexBuffer, TriangleElementsBuffer &elementsBuffer);
+    ~CircleBucket() override;
+
+    void upload() override;
+    void render(Painter&, const StyleLayer&, const TileID&, const mat4&) override;
+
+    bool hasData() const;
+    void addGeometry(const GeometryCollection&);
+
+    void drawCircles(CircleShader& shader);
+
+private:
+    CircleVertexBuffer& vertexBuffer_;
+    TriangleElementsBuffer& elementsBuffer_;
+
+    const size_t vertexStart_;
+    const size_t elementsStart_;
+
+    std::vector<std::unique_ptr<TriangleGroup>> triangleGroups_;
+};
+
+} // namespace mbgl
+
+#endif // MBGL_RENDERER_CIRCLE_BUCKET

src/mbgl/renderer/painter.cpp

@@ -27,6 +27,7 @@
 #include <mbgl/shader/sdf_shader.hpp>
 #include <mbgl/shader/dot_shader.hpp>
 #include <mbgl/shader/box_shader.hpp>
+#include <mbgl/shader/circle_shader.hpp>
 
 #include <mbgl/util/constants.hpp>
 #include <mbgl/util/mat3.hpp>
@@ -66,6 +67,7 @@ void Painter::setup() {
     assert(sdfGlyphShader);
     assert(sdfIconShader);
     assert(dotShader);
+    assert(circleShader);
 
 
     // Blending
@@ -100,6 +102,7 @@ void Painter::setupShaders() {
     if (!sdfIconShader) sdfIconShader = std::make_unique<SDFIconShader>();
     if (!dotShader) dotShader = std::make_unique<DotShader>();
     if (!collisionBoxShader) collisionBoxShader = std::make_unique<CollisionBoxShader>();
+    if (!circleShader) circleShader = std::make_unique<CircleShader>();
 }
 
 void Painter::resize() {

src/mbgl/renderer/painter.hpp

@@ -38,6 +38,7 @@ struct FrameData;
 class DebugBucket;
 class FillBucket;
 class LineBucket;
+class CircleBucket;
 class SymbolBucket;
 class RasterBucket;
 
@@ -50,6 +51,7 @@ class LineShader;
 class LinejoinShader;
 class LineSDFShader;
 class LinepatternShader;
+class CircleShader;
 class PatternShader;
 class IconShader;
 class RasterShader;
@@ -106,6 +108,7 @@ class Painter : private util::noncopyable {
     void renderDebugText(DebugBucket& bucket, const mat4 &matrix);
     void renderFill(FillBucket& bucket, const StyleLayer &layer_desc, const TileID& id, const mat4 &matrix);
     void renderLine(LineBucket& bucket, const StyleLayer &layer_desc, const TileID& id, const mat4 &matrix);
+    void renderCircle(CircleBucket& bucket, const StyleLayer &layer_desc, const TileID& id, const mat4 &matrix);
     void renderSymbol(SymbolBucket& bucket, const StyleLayer &layer_desc, const TileID& id, const mat4 &matrix);
     void renderRaster(RasterBucket& bucket, const StyleLayer &layer_desc, const TileID& id, const mat4 &matrix);
     void renderBackground(const StyleLayer &layer_desc);
@@ -227,6 +230,7 @@ class Painter : private util::noncopyable {
     std::unique_ptr<SDFIconShader> sdfIconShader;
     std::unique_ptr<DotShader> dotShader;
     std::unique_ptr<CollisionBoxShader> collisionBoxShader;
+    std::unique_ptr<CircleShader> circleShader;
 
     StaticVertexBuffer backgroundBuffer = {
         { -1, -1 }, { 1, -1 },