Method startDragDropSource

examples/Showcase/examples_frame.cpp:115–121

  bool isDragDropSource() override { return true; }

  std::string startDragDropSource() override {
    redraw();
    dragging_ = true;
    source_file_ = visage::createTemporaryFile("txt");
    visage::replaceFileWithText(source_file_, "Example drag and drop source file.");
    return source_file_.string();
  }

  void cleanupDragDropSource() override {
    redraw();