port collision box debug rendering

src/mbgl/geometry/collision_box_buffer.cpp

@@ -0,0 +1,27 @@
+#include <mbgl/geometry/collision_box_buffer.hpp>
+#include <mbgl/platform/gl.hpp>
+#include <mbgl/util/math.hpp>
+
+#include <cmath>
+
+namespace mbgl {
+
+size_t CollisionBoxVertexBuffer::add(int16_t x, int16_t y, float ox, float oy, float maxzoom, float placementZoom) {
+    const size_t idx = index();
+    void *data = addElement();
+
+    int16_t *shorts = static_cast<int16_t *>(data);
+    shorts[0] /* pos */ = x;
+    shorts[1] /* pos */ = y;
+    shorts[2] /* offset */ = std::round(ox); // use 1/64 pixels for placement
+    shorts[3] /* offset */ = std::round(oy);
+
+    uint8_t *ubytes = static_cast<uint8_t *>(data);
+    // a_data1
+    ubytes[8] = maxzoom * 10;
+    ubytes[9] = placementZoom * 10;
+
+    return idx;
+}
+
+}