stats.lua: use scroll function for page 2 and 0

Pages 2 and 0 had their own scroll implementations, which worked fine
for ass, but didn't work well in the terminal.

Now they both use the same scroll function as page 4.

That scroll function requires each output line to be one entry
in the table. Page 0 did not adhere to that new requirement, instead
it generated two table entries for a single output line when a graph
is shown. To fulfill that requirement the generated graph now gets
directly appended to the same table entry that's used for the rest
of the line.

player/lua/stats.lua

@@ -277,7 +277,7 @@ local function sorted_keys(t, comp_fn)
     return keys
 end
 
-local function append_perfdata(s, dedicated_page, print_passes)
+local function append_perfdata(header, s, dedicated_page, print_passes)
     local vo_p = mp.get_property_native("vo-passes")
     if not vo_p then
         return
@@ -318,7 +318,8 @@ local function append_perfdata(s, dedicated_page, print_passes)
 
     -- ensure that the fixed title is one element and every scrollable line is
     -- also one single element.
-    s[#s+1] = format("%s%s%s%s{\\fs%s}%s%s{\\fs%s}",
+    local h = dedicated_page and header or s
+    h[#h+1] = format("%s%s%s%s{\\fs%s}%s%s{\\fs%s}",
                      dedicated_page and "" or o.nl, dedicated_page and "" or o.indent,
                      b("Frame Timings:"), o.prefix_sep, o.font_size * 0.66,
                      "(last/average/peak μs)",
@@ -503,32 +504,20 @@ local function get_kbinfo_lines(width)
     return info_lines
 end
 
-local function append_general_perfdata(s, offset)
-    local perf_info = mp.get_property_native("perf-info") or {}
-    local count = 0
-    for _, data in ipairs(perf_info) do
-        count = count + 1
-    end
-    offset = max(1, min((offset or 1), count))
+local function append_general_perfdata(s)
+    for i, data in ipairs(mp.get_property_native("perf-info") or {}) do
+        append(s, data.text or data.value, {prefix="["..tostring(i).."] "..data.name..":"})
 
-    local i = 0
-    for _, data in ipairs(perf_info) do
-        i = i + 1
-        if i >= offset then
-            append(s, data.text or data.value, {prefix="["..tostring(i).."] "..data.name..":"})
-
-            if o.plot_perfdata and o.use_ass and data.value then
-                buf = perf_buffers[data.name]
-                if not buf then
-                    buf = {0, pos = 1, len = 50, max = 0}
-                    perf_buffers[data.name] = buf
-                end
-                graph_add_value(buf, data.value)
-                s[#s+1] = generate_graph(buf, buf.pos, buf.len, buf.max, nil, 0.8, 1)
+        if o.plot_perfdata and o.use_ass and data.value then
+            buf = perf_buffers[data.name]
+            if not buf then
+                buf = {0, pos = 1, len = 50, max = 0}
+                perf_buffers[data.name] = buf
             end
+            graph_add_value(buf, data.value)
+            s[#s] = s[#s] .. generate_graph(buf, buf.pos, buf.len, buf.max, nil, 0.8, 1)
         end
     end
-    return offset
 end
 
 local function append_display_sync(s)
@@ -865,7 +854,7 @@ local function add_video_out(s)
         append_property(s, "frame-drop-count", {suffix=" (output)", nl="", indent=""})
     end
     append_display_sync(s)
-    append_perfdata(s, false, o.print_perfdata_passes)
+    append_perfdata(nil, s, false, o.print_perfdata_passes)
 
     if mp.get_property_native("deinterlace-active") then
         append_property(s, "deinterlace", {prefix="Deinterlacing:"})
@@ -1037,32 +1026,18 @@ local function default_stats()
     return table.concat(stats)
 end
 
-local function scroll_vo_stats(stats, fixed_items, offset)
-    local ret = {}
-    local count = #stats - fixed_items
-    offset = max(1, min((offset or 1), count))
-
-    for i, line in pairs(stats) do
-        if i <= fixed_items or i >= fixed_items + offset then
-            ret[#ret+1] = stats[i]
-        end
-    end
-    return ret, offset
-end
-
 -- Returns an ASS string with extended VO stats
 local function vo_stats()
-    local stats = {}
+    local header, content = {}, {}
     eval_ass_formatting()
-    add_header(stats)
-
-    -- first line (title) added next is considered fixed
-    local fixed_items = #stats + 1
-    append_perfdata(stats, true, true)
+    add_header(header)
+    append_perfdata(header, content, true, true)
+    header = {table.concat(header)}
 
     local page = pages[o.key_page_2]
-    stats, page.offset = scroll_vo_stats(stats, fixed_items, page.offset)
-    return table.concat(stats)
+    local res = nil
+    res, page.offset = compose_page(header, content, page.offset)
+    return res
 end
 
 local kbinfo_lines = nil
@@ -1086,13 +1061,16 @@ local function keybinding_info(after_scroll)
 end
 
 local function perf_stats()
-    local stats = {}
+    local header, content = {}, {}
     eval_ass_formatting()
-    add_header(stats)
+    add_header(header)
     local page = pages[o.key_page_0]
-    append(stats, "", {prefix=page.desc .. ":", nl="", indent=""})
-    page.offset = append_general_perfdata(stats, page.offset)
-    return table.concat(stats)
+    append(header, "", {prefix=page.desc .. ":", nl="", indent=""})
+    append_general_perfdata(content)
+    header = {table.concat(header)}
+    local res = nil
+    res, page.offset = compose_page(header, content, page.offset)
+    return res
 end
 
 local function opt_time(t)