add bottom_padding option for end-of-document scroll position

paul-talma · web-flow · commit c5440c8d0a10 · 2026-04-19T23:21:40.000+02:00
Adds a bottom_padding config option (fraction 0-1) controlling how far from the top of the viewport the final line sits when scrolled to end. Default 0.5 means the last line is scrollable to the vertical midpoint. Value injected into index.html via __BOTTOM_PADDING__ template token with safe data-attribute fallback.
diff --git a/README.md b/README.md
@@ -115,6 +115,10 @@ require("markdown_preview").setup({
   mermaid_renderer = "js",              -- "js" (browser mermaid.js) or "rust" (mmdr CLI, ~400x faster)
 
   scroll_sync = true,                   -- browser follows cursor position
+
+  -- Fraction (0–1): vertical position of the final line when scrolled to end.
+  -- 0.5 = middle of viewport (default), 1.0 = bottom edge (no extra space)
+  bottom_padding = 0.5,
 })
 ```
 
diff --git a/assets/index.html b/assets/index.html
@@ -1,5 +1,5 @@
 <!doctype html>
-<html lang="en" data-theme="dark">
+<html lang="en" data-theme="dark" data-bottom-padding="__BOTTOM_PADDING__">
 
 <head>
     <meta charset="utf-8" />
@@ -839,6 +839,8 @@ <h1>Markdown Preview</h1>
         import mermaid from 'https://cdn.jsdelivr.net/npm/mermaid@11/dist/mermaid.esm.min.mjs';
         import markdownItGithubAlerts from 'https://unpkg.com/markdown-it-github-alerts@1.0.1/dist/index.mjs';
 
+        const BOTTOM_PADDING = parseFloat(document.documentElement.dataset.bottomPadding) || 0.5;
+
         // ── DOM refs ──────────────────────────────────────────────────
         const $ = (id) => document.getElementById(id);
         const contentEl = $('content');
@@ -1176,6 +1178,7 @@ <h1>Markdown Preview</h1>
                 } else {
                     contentEl.innerHTML = html;
                 }
+                applyBottomPadding();
 
                 const blocks = contentEl.querySelectorAll('.mermaid-block[data-mermaid-source]:not(.mermaid-rendered)');
                 for (const block of blocks) {
@@ -1406,6 +1409,12 @@ <h1>Markdown Preview</h1>
             }
         }).observe(contentEl);
 
+        // ── Bottom padding ────────────────────────────────────────────
+        function applyBottomPadding() {
+            contentEl.style.paddingBottom = `${(1 - BOTTOM_PADDING) * window.innerHeight}px`;
+        }
+        window.addEventListener('resize', applyBottomPadding);
+
         // ── Boot ──────────────────────────────────────────────────────
         (async function boot() {
             try {
diff --git a/lua/markdown_preview/init.lua b/lua/markdown_preview/init.lua
@@ -31,10 +31,15 @@ M.config = {
 	mermaid_renderer = "js",
 
 	scroll_sync = true, -- sync browser scroll to cursor position
+
+	-- Fraction (0–1): vertical position of the final line when scrolled to end.
+	-- 0.5 = middle of viewport (default), 1.0 = bottom edge (no extra space)
+	bottom_padding = 0.5,
 }
 
 function M.setup(opts)
 	M.config = vim.tbl_deep_extend("force", M.config, opts or {})
+	M.config.bottom_padding = math.max(0, math.min(1, M.config.bottom_padding))
 	M._mmdr_available = nil -- reset so next check re-probes
 end
 
@@ -83,7 +88,9 @@ local function write_index(dir)
 	if not src then
 		error("Could not locate assets/index.html in runtimepath. Make sure the plugin ships it.")
 	end
-	util.copy_file(src, dst)
+	local content = util.read_text(src)
+	content = content:gsub("__BOTTOM_PADDING__", tostring(M.config.bottom_padding))
+	util.write_text(dst, content)
 	return dst
 end
 
@@ -254,7 +261,7 @@ local function get_content(bufnr)
 		local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
 		text = table.concat(lines, "\n")
 	elseif vim.api.nvim_buf_get_name(bufnr):match("%.mmd$")
-		or vim.api.nvim_buf_get_name(bufnr):match("%.mermaid$") then
+        or vim.api.nvim_buf_get_name(bufnr):match("%.mermaid$") then
 		-- .mmd / .mermaid files: treat entire buffer as mermaid
 		local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
 		text = "```mermaid\n" .. table.concat(lines, "\n") .. "\n```\n"
