Update the Nageru theme for more cameras.

[ultimatescore] / nageru / ultimate.lua

-- Nageru theme for TFK mini-tournament 2017, based on the default theme.

local transition_start = -2.0
local transition_end = -1.0
local transition_type = 0
local transition_src_signal = 0
local transition_dst_signal = 0

local neutral_colors = {
        {0.5, 0.5, 0.5},  -- Input 0.
        {0.5, 0.5, 0.5},  -- Input 1.
        {0.5, 0.5, 0.5},  -- Input 2.
        {0.5, 0.5, 0.5},  -- Input 3.
        {0.5, 0.5, 0.5}   -- Input 4.
}

local overlay_transition_start = -2.0
local overlay_transition_end = -1.0
local overlay_alpha_src = 0.0
local overlay_alpha_dst = 1.0
local overlay_enabled = false

local live_signal_num = 0
local preview_signal_num = 1
local NUM_CAMERAS = 5  -- Remember to update neutral_colors, too.

-- Valid values for live_signal_num and preview_signal_num.
local INPUT0_SIGNAL_NUM = 0
local INPUT1_SIGNAL_NUM = 1
local INPUT2_SIGNAL_NUM = 2
local INPUT3_SIGNAL_NUM = 3
local INPUT4_SIGNAL_NUM = 4
local STATIC_SIGNAL_NUM = NUM_CAMERAS

-- Preview-only signal showing the current signal with the overlay.
-- Not valid for live_signal_num!
local OVERLAY_SIGNAL_NUM = NUM_CAMERAS + 1

-- Valid values for transition_type. (Cuts are done directly, so they need no entry.)
local NO_TRANSITION = 0
local FADE_TRANSITION = 2

-- Last width/height/frame rate for each channel, if we have it.
-- Note that unlike the values we get from Nageru, the resolution is per
-- frame and not per field, since we deinterlace.
local last_resolution = {}

local caspar_input = VideoInput.new("unix:///tmp/caspar.sock", Nageru.VIDEO_FORMAT_BGRA)
caspar_input:change_rate(2.0)

-- Utility function to help creating many similar chains that can differ
-- in a free set of chosen parameters.
function make_cartesian_product(parms, callback)
        return make_cartesian_product_internal(parms, callback, 1, {})
end

function make_cartesian_product_internal(parms, callback, index, args)
        if index > #parms then
                return callback(unpack(args))
        end
        local ret = {}
        for _, value in ipairs(parms[index]) do
                args[index] = value
                ret[value] = make_cartesian_product_internal(parms, callback, index + 1, args)
        end
        return ret
end

-- An overlay with variable alpha.
function make_overlay(chain, base)
        local image = chain:add_video_input(caspar_input, false)
        local multiply_effect = chain:add_effect(MultiplyEffect.new())
        local overlay_effect = chain:add_effect(OverlayEffect.new(), base, multiply_effect)
        return {
                image = image,
                multiply_effect = multiply_effect,
                overlay_effect = overlay_effect
        }
end

function possibly_make_overlay(has_overlay, chain, base)
        if has_overlay == true then
                return make_overlay(chain, base)
        else
                return nil
        end
end

function make_fade_input(chain, signal, live, deint, scale)
        local input, wb_effect, resample_effect, last
        if live then
                input = chain:add_live_input(false, deint)
                input:connect_signal(signal)
                last = input
        else
                input = chain:add_effect(ImageInput.new("tfk_pause.png"))
                last = input
        end

        -- If we cared about this for the non-main inputs, we would have
        -- checked hq here and invoked ResizeEffect instead.
        if scale then
                resample_effect = chain:add_effect(ResampleEffect.new())
                last = resample_effect
        end

        -- Make sure to put the white balance after the scaling (usually more efficient).
        if live then
                wb_effect = chain:add_effect(WhiteBalanceEffect.new())
                last = wb_effect
        end

        return {
                input = input,
                wb_effect = wb_effect,
                resample_effect = resample_effect,
                last = last
        }
end

-- A chain to fade between two inputs, of which either can be a picture
-- or a live input. In practice only used live, but we still support the
-- hq parameter.
function make_fade_chain(input0_live, input0_deint, input0_scale, input1_live, input1_deint, input1_scale, has_overlay, hq)
        local chain = EffectChain.new(16, 9)

        local input0 = make_fade_input(chain, INPUT0_SIGNAL_NUM, input0_live, input0_deint, input0_scale)
        local input1 = make_fade_input(chain, INPUT1_SIGNAL_NUM, input1_live, input1_deint, input1_scale)

        -- If fading between two live inputs, the overlay is put on top.
        -- If fading between the static picture and a live input,
        -- the overlay is put on the live input.
        local overlay = nil
        if input0_live and not input1_live then
                overlay = possibly_make_overlay(has_overlay, chain, input0.last)
                if overlay then
                        input0.last = overlay.overlay_effect
                end
        elseif input1_live and not input0_live then
                overlay = possibly_make_overlay(has_overlay, chain, input1.last)
                if overlay then
                        input1.last = overlay.overlay_effect
                end
        end

        local mix_effect = chain:add_effect(MixEffect.new(), input0.last, input1.last)
        if input0_live and input1_live then
                overlay = possibly_make_overlay(has_overlay, chain, mix_effect)
        end

        chain:finalize(hq)

        return {
                chain = chain,
                input0 = input0,
                input1 = input1,
                mix_effect = mix_effect,
                overlay = overlay
        }
end

-- Chains to fade between two inputs, in various configurations.
local fade_chains = make_cartesian_product({
        {"static", "live", "livedeint"},  -- input0_type
        {true, false},                    -- input0_scale
        {"static", "live", "livedeint"},  -- input1_type
        {true, false},                    -- input1_scale
        {true, false},                    -- has_overlay
        {true}                            -- hq
}, function(input0_type, input0_scale, input1_type, input1_scale, has_overlay, hq)
        local input0_live = (input0_type ~= "static")
        local input1_live = (input1_type ~= "static")
        local input0_deint = (input0_type == "livedeint")
        local input1_deint = (input1_type == "livedeint")
        return make_fade_chain(input0_live, input0_deint, input0_scale, input1_live, input1_deint, input1_scale, has_overlay, hq)
end)

-- A chain to show a single input on screen.
function make_simple_chain(input_deint, input_scale, has_overlay, hq)
        local chain = EffectChain.new(16, 9)

        local input = chain:add_live_input(false, input_deint)
        input:connect_signal(0)  -- First input card. Can be changed whenever you want.

        local resample_effect, resize_effect
        if scale then
                if hq then
                        resample_effect = chain:add_effect(ResampleEffect.new())
                else
                        resize_effect = chain:add_effect(ResizeEffect.new())
                end
        end

        local wb_effect = chain:add_effect(WhiteBalanceEffect.new())
        local overlay = possibly_make_overlay(has_overlay, chain, wb_effect)

        chain:finalize(hq)

        return {
                chain = chain,
                input = input,
                wb_effect = wb_effect,
                resample_effect = resample_effect,
                resize_effect = resize_effect,
                overlay = overlay
        }
end

-- Make all possible combinations of single-input chains.
local simple_chains = make_cartesian_product({
        {"live", "livedeint"},  -- input_type
        {true, false},          -- input_scale
        {true, false},          -- has_overlay
        {true, false}           -- hq
}, function(input_type, input_scale, has_overlay, hq)
        local input_deint = (input_type == "livedeint")
        return make_simple_chain(input_deint, input_scale, has_overlay, hq)
end)

-- A chain to show a single static picture on screen. Never with CasparCG overlay.
local static_chains = make_cartesian_product({
        {true, false}            -- hq
}, function(hq)
        local chain = EffectChain.new(16, 9)
        local chain_input = chain:add_effect(ImageInput.new("tfk_pause.png"))

        chain:finalize(hq)
        return {
                chain = chain
        }
end)

-- A chain to show the overlay and nothing more. LQ only,
-- since it is not a valid live signal.
local overlay_chain_lq = EffectChain.new(16, 9)
local overlay_chain_lq_input = overlay_chain_lq:add_video_input(caspar_input, false)
overlay_chain_lq:finalize(false)

-- Used for indexing into the tables of chains.
function get_input_type(signals, signal_num)
        if signal_num == STATIC_SIGNAL_NUM then
                return "static"
        elseif signals:get_interlaced(signal_num) then
                return "livedeint"
        else
                return "live"
        end
end

function needs_scale(signals, signal_num, width, height)
        if signal_num == STATIC_SIGNAL_NUM then
                -- We assume this is already correctly scaled at load time.
                return false
        end
        assert(is_plain_signal(signal_num))
        return (signals:get_width(signal_num) ~= width or signals:get_height(signal_num) ~= height)
end

function set_scale_parameters_if_needed(chain_or_input, width, height)
        if chain_or_input.resample_effect then
                chain_or_input.resample_effect:set_int("width", width)
                chain_or_input.resample_effect:set_int("height", height)
        elseif chain_or_input.resize_effect then
                chain_or_input.resize_effect:set_int("width", width)
                chain_or_input.resize_effect:set_int("height", height)
        end
end

-- API ENTRY POINT
-- Returns the number of outputs in addition to the live (0) and preview (1).
-- Called only once, at the start of the program.
function num_channels()
        return NUM_CAMERAS + 2  -- static picture and overlay
end

function is_plain_signal(num)
        return num >= INPUT0_SIGNAL_NUM and num <= INPUT4_SIGNAL_NUM
end

-- Helper function to write e.g. “720p60”. The difference between this
-- and get_channel_resolution_raw() is that this one also can say that
-- there's no signal.
function get_channel_resolution(signal_num)
        res = last_resolution[signal_num]
        if (not res) or not res.is_connected then
                return "disconnected"
        end
        if res.height <= 0 then
                return "no signal"
        end
        if not res.has_signal then
                if res.height == 525 then
                        -- Special mode for the USB3 cards.
                        return "no signal"
                end
                return get_channel_resolution_raw(res) .. ", no signal"
        else
                return get_channel_resolution_raw(res)
        end
end

-- Helper function to write e.g. “60” or “59.94”.
function get_frame_rate(res)
        local nom = res.frame_rate_nom
        local den = res.frame_rate_den
        if nom % den == 0 then
                return nom / den
        else
                return string.format("%.2f", nom / den)
        end
end

-- Helper function to write e.g. “720p60”.
function get_channel_resolution_raw(res)
        if res.interlaced then
                return res.height .. "i" .. get_frame_rate(res)
        else
                return res.height .. "p" .. get_frame_rate(res)
        end
end

-- API ENTRY POINT
-- Returns the name for each additional channel (starting from 2).
-- Called at the start of the program, and then each frame for live
-- channels in case they change resolution.
function channel_name(channel)
        local signal_num = channel - 2
        if signal_num == INPUT0_SIGNAL_NUM then
                return "Main (" .. get_channel_resolution(signal_num) .. ")"
        elseif signal_num == INPUT1_SIGNAL_NUM then
                return "Secondary (" .. get_channel_resolution(signal_num) .. ")"
        elseif signal_num == INPUT2_SIGNAL_NUM then
                return "Goal L (" .. get_channel_resolution(signal_num) .. ")"
        elseif signal_num == INPUT3_SIGNAL_NUM then
                return "Goal R (" .. get_channel_resolution(signal_num) .. ")"
        elseif signal_num == INPUT4_SIGNAL_NUM then
                return "Ambience (" .. get_channel_resolution(signal_num) .. ")"
        elseif signal_num == STATIC_SIGNAL_NUM then
                return "Static picture"
        elseif signal_num == OVERLAY_SIGNAL_NUM then
                return "Overlay"
        end
end

-- API ENTRY POINT
-- Returns, given a channel number, which signal it corresponds to (starting from 0).
-- Should return -1 if the channel does not correspond to a simple signal.
-- (The information is used for whether right-click on the channel should bring up
-- an input selector or not.)
-- Called once for each channel, at the start of the program.
-- Will never be called for live (0) or preview (1).
function channel_signal(channel)
        if is_plain_signal(channel) then
                return channel - 2
        else
                return -1
        end
end

-- API ENTRY POINT
-- Called every frame. Returns the color (if any) to paint around the given
-- channel. Returns a CSS color (typically to mark live and preview signals);
-- "transparent" is allowed.
-- Will never be called for live (0) or preview (1).
function channel_color(channel)
        if transition_type ~= NO_TRANSITION then
                if channel_involved_in(channel, transition_src_signal) or
                   channel_involved_in(channel, transition_dst_signal) then
                        return "#f00"
                end
        else
                if channel_involved_in(channel, live_signal_num) then
                        return "#f00"
                end
        end
        if channel_involved_in(channel, preview_signal_num) then
                return "#0f0"
        end
        return "transparent"
end

function channel_involved_in(channel, signal_num)
        if is_plain_signal(signal_num) then
                return channel == (signal_num + 2)
        end
        if signal_num == STATIC_SIGNAL_NUM then
                return (channel == NUM_CAMERAS)
        end
        return false
end

-- API ENTRY POINT
-- Returns if a given channel supports setting white balance (starting from 2).
-- Called only once for each channel, at the start of the program.
function supports_set_wb(channel)
        return is_plain_signal(channel - 2)
end

-- API ENTRY POINT
-- Gets called with a new gray point when the white balance is changing.
-- The color is in linear light (not sRGB gamma).
function set_wb(channel, red, green, blue)
        if is_plain_signal(channel - 2) then
                neutral_colors[channel - 2 + 1] = { red, green, blue }
        end
end

function finish_transitions(t)
        if transition_type ~= NO_TRANSITION and t >= transition_end then
                live_signal_num = transition_dst_signal
                transition_type = NO_TRANSITION
        end

        -- Disable the overlay if it is no longer visible.
        if overlay_enabled and t > overlay_transition_end and overlay_alpha_dst == 0.0 then
                overlay_enabled = false
                print("Turning off overlay")
        end
end

function in_transition(t)
        return t >= transition_start and t <= transition_end
end

-- API ENTRY POINT
-- Called every frame.
function get_transitions(t)
        if preview_signal_num == OVERLAY_SIGNAL_NUM then
                if t < overlay_transition_end then
                        -- Fade in progress.
                        return {}
                end
                if overlay_enabled then
                        return {"Overlay off", "", "Fade ovl out"}
                else
                        return {"Overlay on", "", "Fade ovl in"}
                end
        end

        if in_transition(t) then
                -- Transition already in progress, the only thing we can do is really
                -- cut to the preview. (TODO: Make an “abort” and/or “finish”, too?)
                return {"Cut"}
        end

        if live_signal_num == preview_signal_num then
                -- No transitions possible.
                return {}
        end

        if (is_plain_signal(live_signal_num) or live_signal_num == STATIC_SIGNAL_NUM) and
           (is_plain_signal(preview_signal_num) or preview_signal_num == STATIC_SIGNAL_NUM) then
                return {"Cut", "", "Fade"}
        end

        return {"Cut"}
end

function swap_preview_live()
        local temp = live_signal_num
        live_signal_num = preview_signal_num
        preview_signal_num = temp
end

function start_transition(type_, t, duration)
        transition_start = t
        transition_end = t + duration
        transition_type = type_
        transition_src_signal = live_signal_num
        transition_dst_signal = preview_signal_num
        swap_preview_live()
end

-- API ENTRY POINT
-- Called when the user clicks a transition button.
function transition_clicked(num, t)
        if preview_signal_num == OVERLAY_SIGNAL_NUM then
                if num == 0 then
                        -- Cut.
                        overlay_transition_start = -2.0
                        overlay_transition_end = -1.0
                        if overlay_enabled then
                                overlay_enabled = false
                                overlay_alpha_src = 0.0
                                overlay_alpha_dst = 0.0
                        else
                                overlay_enabled = true
                                overlay_alpha_src = 1.0
                                overlay_alpha_dst = 1.0
                        end
                elseif num == 2 then
                        -- Fade.
                        overlay_transition_start = t
                        overlay_transition_end = t + 1.0
                        if overlay_enabled then
                                overlay_alpha_src = 1.0
                                overlay_alpha_dst = 0.0
                        else
                                overlay_alpha_src = 0.0
                                overlay_alpha_dst = 1.0
                        end
                        overlay_enabled = true
                end
                return
        end

        if num == 0 then
                -- Cut.
                if in_transition(t) then
                        -- Ongoing transition; finish it immediately before the cut.
                        finish_transitions(transition_end)
                end

                swap_preview_live()
        elseif num == 1 then
                -- Zoom.
                finish_transitions(t)

                if live_signal_num == preview_signal_num then
                        -- Nothing to do.
                        return
                end

                if is_plain_signal(live_signal_num) and is_plain_signal(preview_signal_num) then
                        -- We can't zoom between these. Just make a cut.
                        io.write("Cutting from " .. live_signal_num .. " to " .. live_signal_num .. "\n")
                        swap_preview_live()
                        return
                end
        elseif num == 2 then
                finish_transitions(t)

                -- Fade.
                if (live_signal_num ~= preview_signal_num) and
                   (is_plain_signal(live_signal_num) or
                    live_signal_num == STATIC_SIGNAL_NUM) and
                   (is_plain_signal(preview_signal_num) or
                    preview_signal_num == STATIC_SIGNAL_NUM) then
                        start_transition(FADE_TRANSITION, t, 1.0)
                else
                        -- Fades involving SBS are ignored (we have no chain for it).
                end
        end
end

-- API ENTRY POINT
function channel_clicked(num)
        preview_signal_num = num
end

function get_fade_chain(signals, t, width, height, input_resolution)
        local input0_type = get_input_type(signals, transition_src_signal)
        local input0_scale = needs_scale(signals, transition_src_signal, width, height)
        local input1_type = get_input_type(signals, transition_dst_signal)
        local input1_scale = needs_scale(signals, transition_dst_signal, width, height)
        local chain = fade_chains[input0_type][input0_scale][input1_type][input1_scale][overlay_enabled][true]
        prepare = function()
                if input0_type == "live" or input0_type == "livedeint" then
                        chain.input0.input:connect_signal(transition_src_signal)
                        set_neutral_color_from_signal(chain.input0.wb_effect, transition_src_signal)
                end
                set_scale_parameters_if_needed(chain.input0, width, height)
                if input1_type == "live" or input1_type == "livedeint" then
                        chain.input1.input:connect_signal(transition_dst_signal)
                        set_neutral_color_from_signal(chain.input1.wb_effect, transition_dst_signal)
                end
                set_scale_parameters_if_needed(chain.input1, width, height)
                local tt = calc_fade_progress(t, transition_start, transition_end)

                chain.mix_effect:set_float("strength_first", 1.0 - tt)
                chain.mix_effect:set_float("strength_second", tt)
                prepare_overlay_live(chain, t)
        end
        return chain.chain, prepare
end

-- API ENTRY POINT
-- Called every frame. Get the chain for displaying at input <num>,
-- where 0 is live, 1 is preview, 2 is the first channel to display
-- in the bottom bar, and so on up to num_channels()+1. t is the
-- current time in seconds. width and height are the dimensions of
-- the output, although you can ignore them if you don't need them
-- (they're useful if you want to e.g. know what to resample by).
--
-- <signals> is basically an exposed InputState, which you can use to
-- query for information about the signals at the point of the current
-- frame. In particular, you can call get_width() and get_height()
-- for any signal number, and use that to e.g. assist in chain selection.
--
-- You should return two objects; the chain itself, and then a
-- function (taking no parameters) that is run just before rendering.
-- The function needs to call connect_signal on any inputs, so that
-- it gets updated video data for the given frame. (You are allowed
-- to switch which input your input is getting from between frames,
-- but not calling connect_signal results in undefined behavior.)
-- If you want to change any parameters in the chain, this is also
-- the right place.
--
-- NOTE: The chain returned must be finalized with the Y'CbCr flag
-- if and only if num==0.
function get_chain(num, t, width, height, signals)
        local input_resolution = {}
        for signal_num=0,(NUM_CAMERAS-1) do
                local res = {
                        width = signals:get_width(signal_num),
                        height = signals:get_height(signal_num),
                        interlaced = signals:get_interlaced(signal_num),
                        has_signal = signals:get_has_signal(signal_num),
                        is_connected = signals:get_is_connected(signal_num),
                        frame_rate_nom = signals:get_frame_rate_nom(signal_num),
                        frame_rate_den = signals:get_frame_rate_den(signal_num)
                }

                if res.interlaced then
                        -- Convert height from frame height to field height.
                        -- (Needed for e.g. place_rectangle.)
                        res.height = res.height * 2

                        -- Show field rate instead of frame rate; really for cosmetics only
                        -- (and actually contrary to EBU recommendations, although in line
                        -- with typical user expectations).
                        res.frame_rate_nom = res.frame_rate_nom * 2
                end

                input_resolution[signal_num] = res
        end
        last_resolution = input_resolution

        if num == 0 then  -- Live.
                -- See if we're in a transition.
                finish_transitions(t)
                if transition_type == FADE_TRANSITION then
                        return get_fade_chain(signals, t, width, height, input_resolution)
                elseif is_plain_signal(live_signal_num) then
                        local input_type = get_input_type(signals, live_signal_num)
                        local input_scale = needs_scale(signals, live_signal_num, width, height)
                        local chain = simple_chains[input_type][input_scale][overlay_enabled][true]
                        prepare = function()
                                chain.input:connect_signal(live_signal_num)
                                set_scale_parameters_if_needed(chain, width, height)
                                set_neutral_color_from_signal(chain.wb_effect, live_signal_num)
                                prepare_overlay_live(chain, t)
                        end
                        return chain.chain, prepare
                elseif live_signal_num == STATIC_SIGNAL_NUM then  -- Static picture.
                        local chain = static_chains[true]
                        prepare = function()
                                prepare_overlay_live(chain, t)
                        end
                        return chain.chain, prepare
                else
                        assert(false)
                end
        end

        -- We do not show overlays on the individual preview inputs.
        -- The M/E preview matches what we'd put live by doing a transition, as always.
        local show_overlay = false
        if num == 1 then  -- Preview.
                if preview_signal_num == OVERLAY_SIGNAL_NUM then
                        num = live_signal_num + 2
                        show_overlay = not overlay_enabled

                        if transition_type ~= NO_TRANSITION then
                                num = transition_dst_signal + 2
                        end
                else
                        num = preview_signal_num + 2
                        show_overlay = overlay_enabled
                end
        end

        -- Individual preview inputs (usually without overlay).
        if is_plain_signal(num - 2) then
                local signal_num = num - 2
                local input_type = get_input_type(signals, signal_num)
                local input_scale = needs_scale(signals, signal_num, width, height)
                local chain = simple_chains[input_type][input_scale][show_overlay][false]
                prepare = function()
                        chain.input:connect_signal(signal_num)
                        set_scale_parameters_if_needed(chain, width, height)
                        set_neutral_color(chain.wb_effect, neutral_colors[signal_num + 1])
                        prepare_overlay_static(chain, t)
                end
                return chain.chain, prepare
        end
        if num == STATIC_SIGNAL_NUM + 2 then
                local chain = static_chains[false]
                prepare = function()
                        prepare_overlay_static(chain, t)
                end
                return chain.chain, prepare
        end
        if num == OVERLAY_SIGNAL_NUM + 2 then
                prepare = function()
--                      prepare_overlay(overlay_chain_lq, t)
                end
                return overlay_chain_lq, prepare
        end
end

-- This is broken, of course (even for positive numbers), but Lua doesn't give us access to real rounding.
function round(x)
        return math.floor(x + 0.5)
end

function prepare_overlay_live(chain, t)
        if chain.overlay then
                local tt = calc_fade_progress(t, overlay_transition_start, overlay_transition_end)
                overlay_alpha = overlay_alpha_src + tt * (overlay_alpha_dst - overlay_alpha_src)
                --print("overlay_alpha=" .. overlay_alpha .. " [" .. overlay_alpha_src .. "," .. overlay_alpha_dst .. "]@" .. tt)
                if t > overlay_transition_end and overlay_alpha_dst == 0.0 then
                        overlay_enabled = false  -- Takes effect next frame.
        --              print("Turning off overlay")
                end
                chain.overlay.multiply_effect:set_vec4("factor", overlay_alpha, overlay_alpha, overlay_alpha, overlay_alpha)
        end
end

function prepare_overlay_static(chain)
        if chain.overlay then
                chain.overlay.multiply_effect:set_vec4("factor", 1.0, 1.0, 1.0, 1.0)
        end
end

function set_neutral_color(effect, color)
        effect:set_vec3("neutral_color", color[1], color[2], color[3])
end

function set_neutral_color_from_signal(effect, signal)
        if is_plain_signal(signal) then
                set_neutral_color(effect, neutral_colors[signal - INPUT0_SIGNAL_NUM + 1])
        end
end

function calc_zoom_progress(t)
        if t < transition_start then
                return 0.0
        elseif t > transition_end then
                return 1.0
        else
                local tt = (t - transition_start) / (transition_end - transition_start)
                -- Smooth it a bit.
                return math.sin(tt * 3.14159265358 * 0.5)
        end
end

function calc_fade_progress(t, transition_start, transition_end)
        local tt = (t - transition_start) / (transition_end - transition_start)
        if tt < 0.0 then
                return 0.0
        elseif tt > 1.0 then
                return 1.0
        end

        -- Make the fade look maybe a tad more natural, by pumping it
        -- through a sigmoid function.
        tt = 10.0 * tt - 5.0
        tt = 1.0 / (1.0 + math.exp(-tt))

        return tt
end