bufresize.nvim can keep your buffers width and height in proportion when the terminal window is resized. For example, if you have two buffers side by side, with the left buffer taking up 70% of the terminal width and the right buffer taking up 30% of the terminal width. Then if you resized the terminal window, the left buffer and right buffer will still take up 70% and 30% respectively(By default, resizing terminal window does not keep the buffers dimension in proportion).

In addition, bufresize.nvim also support proportional resize when opening or closing a window.

Normally, if you close window D in the below configuration, the height of window D goes to A and C.

Without bufresize
---------------          ---------------
|      |      |          |      |      |
|      |  B   |          |      |  B   |
|  A   |------|          |  A   |------|
|      |  C   |    ->    |      |  C   |
|      |      |          |      |      |
---------------          |      |      |
|      D      |          |      |      |
---------------          ---------------

With bufresize.nvim, we can distribute the height proportionally to B and C as shown below

With bufresize
---------------          ---------------
|      |      |          |      |      |
|      |  B   |          |      |  B   |
|  A   |------|          |  A   |      |
|      |  C   |    ->    |      |------|
|      |      |          |      |      |
---------------          |      |  C   |
|      D      |          |      |      |
---------------          ---------------

The same goes for opening a new window. For example, if you open toggleterm in vertical direction (windows D in the below figure), the initial windows will go out of proportion.

Without bufresize
---------------         ---------------
|      |      |         |      | |    |
|      |  B   |         |      |B|    |
|  A   |      |         |  A   | |    |
|      |------|   ->    |      |-| D  |
|      |      |         |      | |    |
|      |  C   |         |      |C|    |
|      |      |         |      | |    |
---------------         ---------------

With bufresize.nvim, we can resize the windows A, B, and C so that their proportion remains the same after opening toggleterm windows.

With bufresize
---------------         ---------------
|      |      |         |    |   |    |
|      |  B   |         |    | B |    |
|  A   |      |         |  A |   |    |
|      |------|   ->    |    |---| D  |
|      |      |         |    |   |    |
|      |  C   |         |    | C |    |
|      |      |         |    |   |    |
---------------         ---------------

Video demonstrations are available in this pull request

• Neovim 0.5 or higher

with vim-plug

Plug 'kwkarlwang/bufresize.nvim'

with packer.nvim

use {
    "kwkarlwang/bufresize.nvim",
    config = function()
        require("bufresize").setup()
    end
}

This section setup bufresize for resizing terminal window. To setup bufresize for opening and closing window, please see the Exported Functions section.

bufresize.nvim setup provides two options, register and resize. register and resize are tables with two keys, keys and trigger_events. keys is a list of keymappings and trigger_events are a list of vim events that will trigger the function.

register is use to register the current state of buffer windows in the vim, it records the layout, and dimension of each active buffer.

resize is use to apply the registered state to the current state so that the current buffers will have the same proportion as the registered states.

resize also has the key increment, which will round the height and width percent of a window to the nearest increment. For example, with the increment set to 5, if the neovim window now takes up 52.3% of the terminal window width, after resizing, the neovim window width percent will round to the nearest increment, which in this case is 50%. If the increment is set to 2, the neovim window width percent would be round to 52%. To disable rounding to the nearest increment, set increment to false.

use({
    "kwkarlwang/bufresize.nvim",
    config = function()
        local opts = { noremap=true, silent=true }
        require("bufresize").setup({
            register = {
                keys = {
                    { "n", "<leader>w<", "30<C-w><", opts },
                    { "n", "<leader>w>", "30<C-w>>", opts },
                    { "n", "<leader>w+", "10<C-w>+", opts },
                    { "n", "<leader>w-", "10<C-w>-", opts },
                    { "n", "<leader>w_", "<C-w>_", opts },
                    { "n", "<leader>w=", "<C-w>=", opts },
                    { "n", "<leader>w|", "<C-w>|", opts },
                    { "n", "<leader>wo", "<C-w>|<C-w>_", opts },
                },
                trigger_events = { "BufWinEnter", "WinEnter" },
            },
            resize = {
                keys = {},
                trigger_events = { "VimResized" },
                increment = 5,
            },
        })
    end,
})

In this case, if I were to press <leader>w< to resize the buffer window, then the plugin will call register and record the state after the buffer is resized. Suppose I make a new split with :split, then the autocmd event WinEnter will trigger and call register to record the current state.

In the example above, only the event VimResized will trigger the resize function, which take the registered states and apply the proportion of the layout to the current terminal width and height.

use({
    "kwkarlwang/bufresize.nvim",
    config = function()
        local opts = { noremap=true, silent=true }
        require("bufresize").setup({
            register = {
                keys = {
                    { "n", "<C-w><", "<C-w><", opts },
                    { "n", "<C-w>>", "<C-w>>", opts },
                    { "n", "<C-w>+", "<C-w>+", opts },
                    { "n", "<C-w>-", "<C-w>-", opts },
                    { "n", "<C-w>_", "<C-w>_", opts },
                    { "n", "<C-w>=", "<C-w>=", opts },
                    { "n", "<C-w>|", "<C-w>|", opts },
                    { "", "<LeftRelease>", "<LeftRelease>", opts },
                    { "i", "<LeftRelease>", "<LeftRelease><C-o>", opts },
                },
                trigger_events = { "BufWinEnter", "WinEnter" },
            },
            resize = {
                keys = {},
                trigger_events = { "VimResized" },
                increment = false,
            },
        })
    end,
})

If you don't want to call the setup function, you can also bind register and resize as followed.

use({
    "kwkarlwang/bufresize.nvim",
    config = function()
        local opts = { noremap=true, silent=true }
        vim.api.nvim_set_keymap("n", "<C-w><", "<C-w><<cmd>lua require('bufresize').register()<cr>", opts)
        vim.api.nvim_set_keymap("n", "<C-w>>", "<C-w>><cmd>lua require('bufresize').register()<cr>", opts)
        vim.cmd([[
                augroup Resize
                    autocmd!
                    autocmd VimResized * lua require('bufresize').resize()
                augroup END
                ]])
    end,
})

bufresize export the following functions

1. register: record the current windows layout and dimensions. This function is called internally by resize, resize_open, and resize_close
2. resize: apply resize using the registered state, then register the state after resizing. Should be use with VimResized event
3. resize_open: find the newly opened window that is in the current state but not in the registered state, adjust the proportion of registered windows accordingly, then apply resize to the registered windows. Should be use with block_register to prevent race condition
4. resize_close: find the newly closed window that is not in the registered state but not in the current state, adjust the proportion of registered windows accordingly, then apply resize to the registered windows. Should be use with block_register to prevent race condition
5. setup: setup the proportional resize functionality for resizing terminal window. Please see Configuration section for how to setup
6. block_register: prevent register from recording the state. This is useful for resize_open and resize_close if WinEnter and BufWinEnter is in the trigger_events for register. If we don't use block_register, when opening a new window, register might be called before resize_open, which will make resize_open unable to find the newly opened window
7. unblock_register: allow register to record the state. This function is called internally by resize, resize_open, and resize_close after applying the resize and before calling register

My personal usage for resize_open and resize_close is using with toggleterm.

Assuming you have the default configuration for setup, below is my configuration for toggleterm to not mess up the proportion when toggling.

opts = { noremap = true, silent = true }
map = vim.api.nvim_set_keymap
ToggleTerm = function(direction)
    local command = "ToggleTerm"
    if direction == "horizontal" then
        command = command .. " direction=horizontal"
    elseif direction == "vertical" then
        command = command .. " direction=vertical"
    end
    if vim.bo.filetype == "toggleterm" then
        require("bufresize").block_register()
        vim.api.nvim_command(command)
        require("bufresize").resize_close()
    else
        require("bufresize").block_register()
        vim.api.nvim_command(command)
        require("bufresize").resize_open()
        cmd([[execute "normal! i"]])
    end
end
map("n", "<C-s>", ":lua ToggleTerm()<cr>", opts)
map("n", "<leader>ot", [[:lua ToggleTerm("horizontal")<cr>]], opts)
map("n", "<leader>ol", [[:lua ToggleTerm("vertical")<cr>]], opts)
map("i", "<C-s>", "<esc>:lua ToggleTerm()<cr>", opts)
map("t", "<C-s>", "<C-\\><C-n>:lua ToggleTerm()<cr>", opts)

Here is the configuration for applying resize_close for closing windows.

map(
	"t",
	"<leader>wd",
	"<C-\\><C-n>"
		.. ":lua require('bufresize').block_register()<cr>"
		.. "<C-w>c"
		.. ":lua require('bufresize').resize_close()<cr>",
	opts
)
map(
	"n",
	"<leader>wd",
	":lua require('bufresize').block_register()<cr>" .. "<C-w>c" .. ":lua require('bufresize').resize_close()<cr>",
	opts
)