can you control the strength of a glsl shader with a lua script?

[geextahslex]

Hi, I have a lua script that changes the (native mpv) contrast on the fly, I want to also control the strength of a glsl shader that I have.

1. is this possible?
2. how to make this work?

Thanks for any help :)

LUA script

local target_contrast = 0
local current_contrast = 0
local easing_speed = 1.0
local last_update_time = mp.get_time()

local last_value = nil
local last_decision = -9 -- start assuming -9
local value_history = {}
local history_max_size = 30 -- about 0.6 seconds if you update 50x per sec

local base_deadzone = 0.05 -- minimum deadzone width
local max_deadzone = 0.05 -- maximum deadzone width when very noisy

local function ease(current, target, delta_time, speed)
    local alpha = 1 - math.exp(-speed * delta_time)
    return current + (target - current) * alpha
end

local function calculate_deadzone()
    if #value_history < 2 then
        return base_deadzone
    end

    local sum_diff = 0
    for i = 2, #value_history do
        sum_diff = sum_diff + math.abs(value_history[i] - value_history[i-1])
    end

    local avg_diff = sum_diff / (#value_history - 1)

    -- map avg_diff to deadzone size
    local deadzone = math.min(base_deadzone + avg_diff * 5, max_deadzone)

    return deadzone
end

local function check(name, value)
    if value == nil then
        return
    end

    mp.msg.info("Current avg-pq-y value: " .. tostring(value))
	mp.msg.info("Current contrast value: " .. string.format("%.2f", current_contrast))

    table.insert(value_history, value)
    if #value_history > history_max_size then
        table.remove(value_history, 1)
    end

    local deadzone = calculate_deadzone()

    if last_value == nil then
        last_value = value
    end

    if value < 0.2 then
        target_contrast = 0
        last_decision = 0
    elseif value < (0.24 - deadzone) then
        target_contrast = -5
        last_decision = -5
    elseif value > (0.24 + deadzone) then
        target_contrast = -9
        last_decision = -9
    else
        -- within adaptive deadzone, stick to last decision
        target_contrast = last_decision
    end

    last_value = value
end

local function update_contrast()
    local now = mp.get_time()
    local delta_time = now - last_update_time
    last_update_time = now
    local new_contrast = ease(current_contrast, target_contrast, delta_time, easing_speed)
    if math.abs(new_contrast - current_contrast) > 0.01 then
        current_contrast = new_contrast
        mp.set_property("contrast", string.format("%.2f", current_contrast))
    end
end

mp.observe_property("video-out-params/avg-pq-y", "native", check)
mp.add_periodic_timer(0.02, update_contrast)

GLSL shader:

//!PARAM S
//!DESC sCurve Strength
//!TYPE float
//!MINIMUM 0
//!MAXIMUM 1
0.01

//!HOOK LUMA
//!BIND HOOKED
//!DESC sCurve (sigmoid)

#define EFFECT_START           vec3(5.0)   // start applying the effect here
#define EFFECT_START_RAMP_SIZE vec3(35.0)  // smooth out the start of the effect

#define EFFECT_END             vec3(150.0)  // stop applying the effect here
#define EFFECT_END_RAMP_SIZE   vec3(40.0)  // smooth out the edge of the effect

vec4 hook() {
    vec4 orig = HOOKED_tex(HOOKED_pos);
    vec3 effect = mix(orig.rgb, 1.0 - (1.0 / (1.0 + exp(-14.0 * orig.rgb + 7.0))), S); // your desired effect.
    
    // Calculate the smoothstep for the start and end effect
    vec3 start_mmix = smoothstep(EFFECT_START, 
                                 EFFECT_START + EFFECT_START_RAMP_SIZE, 
                                 orig.rgb * 255.0);
    
    vec3 end_mmix = smoothstep(EFFECT_END - EFFECT_END_RAMP_SIZE * 0.5, 
                               EFFECT_END + EFFECT_END_RAMP_SIZE * 0.5, 
                               orig.rgb * 255.0);
    
    // Combine the start and end smoothsteps
    vec3 mmix = 1.0 - (start_mmix * (1.0 - end_mmix));
    
    vec3 out_color = mix(effect, orig.rgb, mmix);
    
    return vec4(out_color, orig.a);
}

[hooke007]

https://mpv.io/manual/master/#options-glsl-shader-opts