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--[[ 50-smooth_scroll.lua — animate a half-page scroll.
Steps <C-e>/<C-y> (plus j/k) over a short timer.
User commands:
`ScrollSmoothDown`: scroll down smoothly
`ScrollSmoothUp`: scroll up smoothly
Keymaps:
`<C-d>` scroll down smoothly
`<C-u>` scroll up smoothly
]]
local Dir = {
UP = 1,
DOWN = 2,
}
local function smooth_scroll(dir)
local scroll_at_boundary, cursor_at_boundary
if dir == Dir.DOWN then
scroll_at_boundary = function()
return vim.fn.line("w$") == vim.api.nvim_buf_line_count(0)
end
cursor_at_boundary = function()
return vim.fn.line(".") == vim.api.nvim_buf_line_count(0)
end
else
scroll_at_boundary = function()
return vim.fn.line("w0") == 1
end
cursor_at_boundary = function()
return vim.fn.line(".") == 1
end
end
--[[ Bail only when the cursor itself can't move further.
At the viewport boundary <C-e>/<C-y> no-op but we still want j/k to walk the cursor. ]]
if cursor_at_boundary() then
return
end
local win_height = vim.api.nvim_win_get_height(0)
local duration, sleep_duration = 100, 16 -- 60 fps
local distance = math.floor(win_height / 2)
-- We want a movement every `sleep_duration` msec
local steps_number = math.ceil(duration / sleep_duration)
local step = distance / steps_number
local scroll_keys = dir == Dir.DOWN and "\\<C-e>j" or "\\<C-y>k"
local cursor_keys = dir == Dir.DOWN and "j" or "k"
local prev = 0
for i = 1, steps_number do
local cur = math.ceil(step * i)
local delta = cur - prev
prev = cur
vim.defer_fn(function()
for _ = 1, delta do
if cursor_at_boundary() then
return
end
-- past the viewport boundary <C-e>/<C-y> no-op; just walk the cursor
local keys = scroll_at_boundary() and cursor_keys or scroll_keys
vim.cmd('exec "normal! ' .. keys .. '"')
end
end, sleep_duration * i)
end
end
local function smooth_scroll_up()
smooth_scroll(Dir.UP)
end
local function smooth_scroll_down()
smooth_scroll(Dir.DOWN)
end
----------------------------------------------------------------------------------------------------
vim.api.nvim_create_user_command(
"ScrollSmoothDown",
smooth_scroll_down,
{ desc = "Scroll down smoothly" }
)
vim.api.nvim_create_user_command(
"ScrollSmoothUp",
smooth_scroll_up,
{ desc = "Scroll up smoothly" }
)
vim.keymap.set("n", "<C-d>", smooth_scroll_down, { desc = "Scroll down smoothly" })
vim.keymap.set("n", "<C-u>", smooth_scroll_up, { desc = "Scroll up smoothly" })
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