Simple delay with feedback for ProtoplugFX

delay.lua

--[[
name: Simple Delay
description: Simple delay with feedback
author: carndt
--]]

require "include/protoplug"

-- Delay line state
local buf, buflen, writepos, sr
-- Plugin params
local length, feedback, drywetmix

-- 'prepareToPlay' will be triggered when the host sample rate is known,
plugin.addHandler('prepareToPlay', function()
    sr = plugin.getSampleRate()
    buflen = sr * 5
    buf = ffi.new("double[?]", buflen)
    writepos = 0
    setLength(250)
end)

function plugin.processBlock(samples, smax)
    for i = 0, smax do
        -- Read from delay line with fixed delay length in samples
        local readpos = writepos - length

        -- wrap around sample read position index
        if readpos < 0 then
            readpos = buflen + readpos
        end

        local out = buf[readpos]

        -- Read left and write sample from input buffer,
        local left, right = samples[0][i], samples[1][i]
        -- mix them with delay according to dry/wet mix param
        -- and set the left and right output samples
        local wetsignal = out * drywetmix
        samples[0][i] = left * (1 - drywetmix) + wetsignal
        samples[1][i] = right * (1 - drywetmix) + wetsignal
        -- Save mono mix of input mixed with delay, attenuated by feedback,
        -- to delay line at current write position
        buf[writepos] = (left + right) / 2 + out * feedback

        -- Increase delay position pointer
        writepos = writepos + 1
        if writepos >= buflen then writepos = 0 end
    end
end

function setLength(val)
    if plugin.isSampleRateKnown() then
        length = val / 1000 * plugin.getSampleRate()
    end
end

params = plugin.manageParams {
    {
        name = "Length (ms)",
        type = "int",
        min = 1,
        max = 5000,
        default = 250,
        changed = setLength
    },
    {
        name = "Feedback",
        type = "int",
        max = 100,
        default = 1,
        changed = function(val) feedback = val / 100 end
    },
    {
        name = "Dry/Wet Mix",
        type = "int",
        min = -100,
        max = 100,
        default = 0,
        changed = function(val) drywetmix = (val + 100) / 201 end
    }
}