lua_opcall
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## lua_opcall

lua_opcall — Calls a Lua opcode at i-rate only. Any number of output and/or input arguments may be passed. All arguments must be passed on the right-hand side. Outputs are returned in the argument.

## Syntax

    lua_iopcall Sname, ...

    lua_ikopcall Sname, ...

    lua_iaopcall Sname, ...

    lua_iopcall_off Sname, ...

    lua_ikopcall_off Sname, ...

    lua_iaopcall_off Sname, ...

## Initialization and Performance

Sname -- The name of the opcode.

... -- An arbitrary list of any number of output and input arguments, of any type. The number, sequence, and types of these arguments must agree with the cdef of the arguments structure that is declared in the corresponding `lua_opdef` opcode.

`lua_iopcall` calls a Lua opcode at i-rate only. Requires `opname_init` to be defined in Lua.

`lua_ikopcall` calls a Lua opcode at i-rate and k-rate. Requires `opname_init` and `opname_kontrol` to be defined in Lua.

`lua_iaopcall` calls a Lua opcode at i-rate and a-rate. Requires `opname_init` and `opname_audio` to be defined in Lua.

`lua_iopcall_off` calls a Lua opcode at i-rate only. Requires `opname_init` and `opname_noteoff` to be defined in Lua.

`lua_ikopcall_off` calls a Lua opcode at i-rate and k-rate. Requires `opname_init`, `opname_kontrol`, and `opname_noteoff` to be defined in Lua.

`lua_iaopcall_off` calls a Lua opcode at i-rate and a-rate. Requires `opname_init`, `opname_audio`, and `opname_noteoff` to be defined in Lua.

Lua code accesses elements of arguments as follows (pointers to both scalars and arrays are dereferenced by the Lua array access operator):

                ffi.cdef(' struct arguments_t { double *a_out, double *i_in, double *i_txt, double *f_sig };');
                local arguments = ffi.cast("struct arguments_t *", carguments_lightuserdata)
                for i = 0, ksmps -1 do begin carguments.a_out[i] = carguments.i_in[0] * 3 end end

The "off" variants of the opcode always schedule a "note off" event that is called when the intrument instance is removed from the active list, and which can be used to release unneeded resources, reschedule the instrument to render a reverb tail, and so on.

## Example

Here is an example of a Lua opcode, showing how to pass strings back and forth between Lua opcodes and Csound orchestra code. The example uses the file luaopcode.csd.

Example 524. Example of a Lua opcode.

    <CsoundSynthesizer>

    <CsInstruments>
    lua_opdef "luatest", {{
    local ffi = require("ffi")
    local string = require("string")
    local csoundLibrary = ffi.load('csound64.dll.5.2')
    ffi.cdef[[
        int csoundGetKsmps(void *);
        double csoundGetSr(void *);
        struct luatest_arguments {double *out; double *stringout; char *stringin; double *in1; double *in2; double sr; int ksmps; };
    ]]
    function luatest_init(csound, opcode, carguments)
        local arguments = ffi.cast("struct luatest_arguments *", carguments)
        arguments.sr = csoundLibrary.csoundGetSr(csound)
        print(string.format('stringin: %s', ffi.string(arguments.stringin)))
        print(string.format('sr: %f', arguments.sr))
        arguments.ksmps = csoundLibrary.csoundGetKsmps(csound)
        print(string.format('ksmps: %d', arguments.ksmps))
        arguments.out[0] = arguments.in1[0] * arguments.in2[0]
        ffi.copy(arguments.stringout, 'Hello, world!')
        return 0
    end
    function luatest_kontrol(csound, opcode, carguments)
        local arguments = ffi.cast("struct luatest_arguments *", carguments)
        arguments.out[0] = arguments.in1[0] * arguments.in2[0]
        return 0
    end
    function luatest_noteoff(csound, opcode, carguments)
        local arguments = ffi.cast("struct luatest_arguments *", carguments)
        arguments.out[0] = arguments.in1[0] * arguments.in2[0]
        print('off')
        return 0
    end
    }}

    instr 1
        iresult = 0
        Stringin = "stringin"
        Stringout = "stringout"
        lua_iopcall "luatest", iresult, Stringout, Stringin, p2, p3
        prints Stringout
    endin
    instr 2
        iresult = 0
        Stringin = "stringin"
        Stringout = "initial value"
        lua_iopcall_off "luatest", iresult, Stringout, Stringin, p2, p3
        print iresult
        prints Stringout
    endin
    </CsInstruments>

    <CsScore>
    i 1 1 2
    i 2 2 2
    i 1 3 2
    e
    </CsScore>

    </CsoundSynthesizer>

## See Also

lua_exec, lua_opdef.

## Credits

By: Michael Gogins 2011

New in Csound version 5.13.2

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