Add circle render type

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

Part of #1740.

1 files changed, 92 insertions, 0 deletions

diff --git a/src/mbgl/renderer/circle_bucket.cpp b/src/mbgl/renderer/circle_bucket.cpp
new file mode 100644
index 0000000000..fde04df29a
--- /dev/null
+++ b/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;
+    }
+}