Function aflak_imgui_sys::igBeginDragDropSource

pub unsafe extern "C" fn igBeginDragDropSource(
    flags: ImGuiDragDropFlags, 
    mouse_button: c_int
) -> bool

Call when current ID is active.

When this returns true you need to:

1. call igSetDragDropPayload exactly once,
2. you may render the payload visual/description,
3. pcall igEndDragDropSource