The "Open files from applications" preference in the General preference pane
gives more options on how dropped files should open, in case tabs are not
desired. See :h macvim-drag-n-drop
.
After setting up dropped files to be opened in splits, they will be opened in horizontal splits by default. If you prefer vertical splits, execute the following command. See :h macvim-user-defaults
.
defaults write org.vim.MacVim MMVerticalSplit -bool TRUE
Also, you could add the following snippet to your ~/.vimrc
file to automatically set these defaults.
if has('gui_running') && has('macunix')
" open dropped files in vertical splits
call system('defaults write org.vim.MacVim MMOpenLayout -bool TRUE')
call system('defaults write org.vim.MacVim MMVerticalSplit -bool TRUE')
endif