How can I use drag and drop attachment When I send a mail using Gmail API?

Question

When I send a email to other people using gmail, I can send both text and images.

Especially, I can send images using drag and drop attachment like below screen shot.

enter image description here

but, How can I use this function using Gmail API???

I can find File Uploading Attachment.

but I wanna implement drag and drop attachment, especially screen shot like above, using Gmail API Can you help me about it ??

Thanks.