Added CircleVertexBuffer class

Part of #1740.

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/vector_tile_data.hpp

@@ -7,6 +7,7 @@
 #include <mbgl/geometry/icon_buffer.hpp>
 #include <mbgl/geometry/line_buffer.hpp>
 #include <mbgl/geometry/text_buffer.hpp>
+#include <mbgl/geometry/circle_buffer.hpp>
 #include <mbgl/geometry/collision_box_buffer.hpp>
 
 #include <iosfwd>
@@ -62,6 +63,7 @@ class VectorTileData : public TileData {
     // Holds the actual geometries in this tile.
     FillVertexBuffer fillVertexBuffer;
     LineVertexBuffer lineVertexBuffer;
+    CircleVertexBuffer circleVertexBuffer;
 
     TriangleElementsBuffer triangleElementsBuffer;
     LineElementsBuffer lineElementsBuffer;