Virtual padding ignores render_offset_top, image overlaps buffer content below

[Haegin]

Problem

When an image is rendered with both with_virtual_padding = true and render_offset_top > 0, the virtual padding reservation does not include the offset. The image visually shifts down by render_offset_top cells (per lua/image/renderer.lua:200), but lua/image/image.lua:125 reserves only height virtual lines instead of height + render_offset_top. The image therefore overlaps the next render_offset_top lines of real buffer content immediately below the reserved area.

This is most visible with diagram.nvim, which always sets render_offset_top = 1 — every rendered diagram covers the first line of buffer content following the diagram block.

Steps to reproduce

/tmp/repro-init.lua:

local lazypath = vim.fn.stdpath("data") .. "/lazy/lazy.nvim"
if not vim.uv.fs_stat(lazypath) then
  vim.fn.system({ "git", "clone", "--filter=blob:none",
    "https://github.com/folke/lazy.nvim.git", "--branch=stable", lazypath })
end
vim.opt.rtp:prepend(lazypath)

require("lazy").setup({
  { "3rd/image.nvim",
    dependencies = { "nvim-lua/plenary.nvim" },
    opts = {
      backend = "kitty",
      kitty_method = "normal",
      max_width_window_percentage = 100,
      max_height_window_percentage = 100,
    },
  },
})

vim.defer_fn(function()
  local image = require("image")
  local img = image.from_file(vim.env.IMG_PATH, {
    buffer = vim.api.nvim_get_current_buf(),
    window = vim.api.nvim_get_current_win(),
    with_virtual_padding = true,
    inline = true,
    x = 0,
    y = 0,
    render_offset_top = 1,
  })
  img:render()
end, 200)

/tmp/repro.txt:

ANCHOR (image renders here, render_offset_top = 1)
THIS LINE IS OVERLAPPED BY THE BOTTOM ROW OF THE IMAGE

Run in a Kitty-graphics-capable terminal (Kitty, Ghostty, etc.):

IMG_PATH=/path/to/any.png nvim --clean -u /tmp/repro-init.lua /tmp/repro.txt

The second line is partially or fully covered by the bottom row of the image. With render_offset_top = 0 (or by patching total_lines per the suggested fix below), it stays visible.

Expected behavior

When render_offset_top = N, the reservation should cover image_rows + N lines so the rendered image (occupying extmark_row + N + 1 through extmark_row + N + image_rows) fits inside the reserved area without overlapping subsequent buffer lines.

Suggested fix

lua/image/image.lua:111 already computes total_height = height + (self.render_offset_top or 0) for the cache-invalidation key. Use the same value for the actual reservation on line 125:

 if self.with_virtual_padding then
   -- only reserve real height for the extmark, padding is applied during rendering
-  local total_lines = height
+  local total_lines = total_height
   for _ = 0, total_lines - 1 do
     filler[#filler + 1] = { { " ", "" } }
   end
   extmark_opts.virt_lines = filler
 end

Environment

• image.nvim: v1.5.1 (commit da2be65)
• Surfaced via diagram.nvim's mermaid integration on Ghostty