Add A/B loop points visual indicator

[NeoLc]

Expected behavior of the wanted feature

-- ** AI Coding use gemini **

local function draw_a_b_range(element, elem_ass)
    --log("Name:", element.name, "Width:", elem_geo.w, "Type:", element.type)
    if element.name ~= "seekbar" then return end

    local duration = mp.get_property_number("duration")
    local ab_a = mp.get_property_number("ab-loop-a")
    local ab_b = mp.get_property_number("ab-loop-b")
    if not duration or duration <= 0 or not ab_a or ab_a < 0 then return end

    local slider_lo = element.layout.slider
    local elem_geo = element.layout.geometry

    ----------------------------------------------------------------
    -- 🎯 第一步：实现类似 t2x 的坐标映射逻辑
    ----------------------------------------------------------------
    local margin = slider_lo.margin or 3
    local usable_width = elem_geo.w - (margin * 2)

    local function t2x(sec)
        local pos = sec / duration
        if pos < 0 then pos = 0 elseif pos > 1 then pos = 1 end
        -- 核心映射公式：起始边距 + (比例 * 有效宽度)
        return margin + (pos * usable_width)
    end

    ----------------------------------------------------------------
    -- 🎯 第二步：计算 A 和 B 的 X 坐标
    ----------------------------------------------------------------
    local ax = t2x(ab_a)
    local bx = (ab_b and ab_b > ab_a and ab_b <= duration) and t2x(ab_b) or nil

    local function draw_nibble(ass, s)
        if slider_lo.gap >= 5 then
            local bar_h = 3
            if slider_lo.nibbles_top then
                if slider_lo.nibbles_style == "triangle" then
                    ass:move_to(s - 3, slider_lo.gap - 5)
                    ass:line_to(s + 3, slider_lo.gap - 5)
                    ass:line_to(s, slider_lo.gap - 1)
                elseif slider_lo.nibbles_style == "bar" then
                    ass:rect_cw(s - 1, slider_lo.gap - bar_h, s + 1, slider_lo.gap)
                else
                    ass:rect_cw(s - 1, slider_lo.gap - bar_h, s + 1, elem_geo.h - slider_lo.gap)
                end
            end
            if slider_lo.nibbles_bottom then
                if slider_lo.nibbles_style == "triangle" then
                    ass:move_to(s - 3, elem_geo.h - slider_lo.gap + 5)
                    ass:line_to(s, elem_geo.h - slider_lo.gap + 1)
                    ass:line_to(s + 3, elem_geo.h - slider_lo.gap + 5)
                elseif slider_lo.nibbles_style == "bar" then
                    ass:rect_cw(s - 1, elem_geo.h - slider_lo.gap, s + 1, elem_geo.h - slider_lo.gap + bar_h)
                else
                    ass:rect_cw(s - 1, slider_lo.gap, s + 1, elem_geo.h - slider_lo.gap + bar_h)
                end
            end
        else
            if slider_lo.nibbles_top then
                ass:rect_cw(s - 1, 0, s + 1, slider_lo.gap)
            end
            if slider_lo.nibbles_bottom then
                ass:rect_cw(s - 1, elem_geo.h - slider_lo.gap, s + 1, elem_geo.h)
            end
        end
    end

    ----------------------------------------------------------------
    -- 🎯 第三步：绘制 A 和 B 的 浮标
    ----------------------------------------------------------------
    if ax then 
        draw_nibble(elem_ass, ax)
    end
    
    if bx then 
        draw_nibble(elem_ass, bx)
    end
end

local function draw_seekbar_nibbles(element, elem_ass)
   -- ...
   draw_a_b_range(element, elem_ass)
   -- ...
end

[Samillion]

I like the idea. Would a color be a better choice instead of markers? To not be mistaken for chapter markers.

user_opts.ab_loop_color = "#2596be"

local function draw_ab_loop_range(element, elem_ass)
    if element.name ~= "seekbar" then return end
    local ab_a = mp.get_property_number("ab-loop-a")
    if not state.duration or not ab_a or ab_a < 0 then return end

    local ab_b = mp.get_property_number("ab-loop-b")
    local slider_lo = element.layout.slider
    local elem_geo = element.layout.geometry

    local ax = get_slider_ele_pos_for(element, ab_a / state.duration * 100)
    local bx = (ab_b and ab_b > ab_a and ab_b <= state.duration)
        and get_slider_ele_pos_for(element, ab_b / state.duration * 100)
        or elem_geo.w

    if ax >= bx then return end

    begin_draw_layer(element, elem_ass, user_opts.ab_loop_color)
    elem_ass:rect_cw(ax, slider_lo.gap, bx, elem_geo.h - slider_lo.gap)
end

[Samillion]

Script: modernz.lua
Commit: 750a410

Changes:

• Show a visual indicator for A/B loop in seek ranges
  • Add ab_loop_color option with a value of #2596be
  • Add draw_ab_loop_range() helper to draw A/B loop indicator in seek ranges
  • Disable A/B loop on new file start

[Samillion]

I only have one hesitation. By default, mpv retains A/B loop even if a new file starts. Meaning you have to clear it manually.

However, I made it so it's disabled on new file starts:

mp.register_event("start-file", function()
+   -- reset ab loop on new file start
+   mp.set_property("ab-loop-a", "no")
+   mp.set_property("ab-loop-b", "no")
    request_init()
end)

My question: Should it disable it or follow mpv default behavior and keep it across file loads/start?

Edit:
Asked the guys on irc, basically this was overlooked. I believe It should be disabled on new file starts as it doesn't make sense to hold the same specific A/B loop range for different files.

Though I'm open to suggestions.

[Shio1999]

could you also add a physical bottom for it?

[Samillion]

could you also add a physical bottom for it?

Since this is a niche feature, the likelihood of adding a dedicated button is not high.

However, this is already accessible through context-menu (Playback => Set A/B Loop), and also in input.conf with x ab-loop, change x to whichever keybind you prefer.

[Samillion]

could you also add a physical bottom for it?

I forgot, you can also make the current loop button right click trigger it

# modernz.conf
file_loop_mbtn_right_command=ab-loop

Alternatively, you can adjust the Play/Pause button mouse commands:

play_pause_mbtn_mid_command=cycle-values loop-playlist inf no
play_pause_mbtn_right_command=cycle-values loop-file inf no