08-table-lookup.py - Table as transfer function.
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In computer science, a lookup table is an array that replaces runtime computation
with a simpler array indexing operation. The savings in terms of processing time
can be significant, since retrieving a value from memory is often faster than 
undergoing an "expensive" computation.

This technic is also used a lot in audio synthesis, where the waveform can be
pre-computed and stored in a table, then simply readed with a ramp at the desired
frequency.

.. code-block:: python

    from pyo import *
    
    s = Server().boot()
    
    src = SfPlayer("../snds/flute.aif", loop=True)
    
    # Arctangent transfer function table.
    table = AtanTable(slope=0.5, size=512)
    table.view()
    
    # A signal to dynamically control the drive of the transfer function.
    drive = Sig(0.5)
    
    # We give it True to the dataonly argument when opening the sliders window,
    # otherwise the table would be rewrite way too often.
    drive.ctrl([SLMap(0, 1, "lin", "value", 0.5, dataOnly=True)], title="Transfer fonction slope")
    
    # Lookup reads a table given an audio index lying between -1 and 1.
    # It is especially designed to scan a transfer function with an audio signal.
    look = Lookup(table, index=src, mul=0.5).out()
    
    # Function called to redraw the transfer function.
    def redraw():
        table.slope = drive.get()
    
    
    # We call the "redraw" function every time the "drive" value changes.
    trig = TrigFunc(Change(drive), function=redraw)
    
    sc = Scope(look)
    
    s.gui(locals())