fe891d581d
- Changing API for time values from float to double for better precision. - Fixing minor mistakes in the documentation. - Fixing minor unnecessary large memory allocation.
241 lines
8.0 KiB
ReStructuredText
241 lines
8.0 KiB
ReStructuredText
Tutorials
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=========
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Introduction
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------------
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The C and Python binding for audaspace were designed with simplicity in mind.
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This means however that to use the full capabilities of audaspace,
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there is no way around the C++ library.
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Simple Demo
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-----------
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The **simple.py** example program contains all the basic
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building blocks for an application using audaspace.
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These building blocks are basically the classes :class:`aud.Device`,
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:class:`aud.Sound` and :class:`aud.Handle`.
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We start with importing :mod:`aud` and :mod:`time`
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as the modules we need for our simple example.
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.. code-block:: python
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#!/usr/bin/python
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import aud, time
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The first step now is to open an output device and this
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can simply be done by allocating a :class:`aud.Device` object.
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.. code-block:: python
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device = aud.Device()
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To create a sound we can choose to load one from a :func:`aud.Sound.file`,
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or we use one of our signal generators. We decide to do the latter
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and create a :func:`aud.Sound.sine` signal with a frequency of 440 Hz.
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.. code-block:: python
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sine = aud.Sound.sine(440)
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.. note:: At this point nothing is playing back yet,
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:class:`aud.Sound` objects are just descriptions of sounds.
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However instead of a sine wave, we would like to have a square wave
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to produce a more retro gaming sound. We could of course use the
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:func:`aud.Sound.square` generator instead of sine,
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but we want to show how to apply effects,
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so we apply a :func:`aud.Sound.threshold`
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which makes a square wave out of our sine too,
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even if less efficient than directly generating the square wave.
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.. code-block:: python
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square = sine.threshold()
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.. note:: The :class:`aud.Sound` class offers generator and effect functions.
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The we can play our sound by calling the
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:func:`aud.Device.play` method of our device.
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This method returns a :class:`aud.Handle`
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which is used to control the playback of the sound.
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.. code-block:: python
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handle = device.play(square)
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Now if we do nothing else anymore the application will quit immediately,
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so we won't hear much of our square wave,
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so we decide to wait for three seconds before
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quitting the application by calling :func:`time.sleep`.
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.. code-block:: python
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time.sleep(3)
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Audioplayer
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-----------
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Now that we know the basics of audaspace,
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we can build our own music player easily
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by just slightly changing the previous program.
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The **player.py** example does exactly that,
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let's have a short look at the differences:
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Instead of creating a sine signal and thresholding it,
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we in fact use the :func:`aud.Sound.file` function to load a sound from a file.
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The filename we pass is the first command line argument our application got.
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.. code-block:: python
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sound = aud.Sound.file(sys.argv[1])
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When the sound gets played back we now want to wait until
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the whole file has been played, so we use the :data:`aud.Handle.status`
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property to determine whether the sound finished playing.
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.. code-block:: python
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while handle.status:
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time.sleep(0.1)
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We don't make any error checks if the user actually added a command
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line argument. As an exercise you could extend this program to play
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any number of command line supplied files in sequence.
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Siren
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-----
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Let's get a little bit more complex. The **siren.py** example
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plays a generated siren sound that circles around your head.
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Depending on how many speakers you have and if the output
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device used supports the speaker setup, you will hear this effect.
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With stereo speakers you should at least hear some left-right-panning.
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We start off again with importing the modules we need and
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we also define some properties of our siren sound.
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We want it to consist of two sine sounds with different frequencies.
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We define a length for the sine sounds and how long a fade in/out should take.
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We also know already how to open a device.
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.. code-block:: python
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#!/usr/bin/python
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import aud, math, time
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length = 0.5
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fadelength = 0.05
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device = aud.Device()
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The next thing to do is to define our sine waves and apply all the required effects.
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As each of the effect functions returns the corresponding sound,
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we can easily chain those calls together.
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.. code-block:: python
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high = aud.Sound.sine(880).limit(0, length).fadein(0, fadelength).fadeout(length - fadelength, length)
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low = aud.Sound.sine(700).limit(0, length).fadein(0, fadelength).fadeout(length - fadelength, length).volume(0.6)
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The next step is to connect the two sines,
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which we do using the :func:`aud.Sound.join` function.
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.. code-block:: python
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sound = high.join(low)
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The generated siren sound can now be played back and what we also do is to loop it.
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Therefore we set the :data:`aud.Handle.loop_count` to a negative value to loop forever.
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.. code-block:: python
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handle = device.play(sound)
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handle.loop_count = -1
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Now we use some timing code to make sure our demo runs for 10 seconds,
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but we also use the time to update the location of our playing sound,
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with the :data:`aud.Handle.location` property, which is a three dimensional vector.
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The trigonometic calculation based on the running time of the program keeps
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the sound on the XZ plane letting it follow a circle around us.
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.. code-block:: python
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start = time.time()
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while time.time() - start < 10:
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angle = time.time() - start
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handle.location = [math.sin(angle), 0, -math.cos(angle)]
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As an exercise you could try to let the sound come from the far left
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and go to the far right and a little bit in front of you within the
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10 second runtime of the program. With this change you should be able
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to hear the volume of the sound change, depending on how far it is away from you.
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Updating the :data:`aud.Handle.velocity` property properly also enables the doppler effect.
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Compare your solution to the **siren2.py** demo.
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Tetris
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------
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The **tetris.py** demo application shows an even more
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complex application which generates retro tetris music.
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Looking at the source code there should be nothing new here,
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again the functions used from audaspace are the same as in the previous examples.
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In the :func:`parseNote` function all single notes get joined which leads
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to a very long chain of sounds. If you think of :func:`aud.Sound.join`
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as a function that creates a binary tree with the two joined sounds as
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leaves then the :func:`parseNote` function creates a very unbalanced tree.
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Insted we could rewrite the code to use two other classes:
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:class:`aud.Sequence` and :class:`aud.SequenceEntry` to sequence the notes.
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The **tetris2.py** application does exactly that.
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Before the while loop we add a variable that stores the current position
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in the score and create a new :class:`aud.Sequence` object.
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.. code-block:: python
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position = 0
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sequence = aud.Sequence()
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Then in the loop we can create the note simply by chaining the
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:func:`aud.Sound.square` generator and :func:`aud.Sound.fadein`
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and :func:`aud.Sound.fadeout` effects.
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.. code-block:: python
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note = aud.Sound.square(freq, rate).fadein(0, fadelength).fadeout(length - fadelength, fadelength)
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Now instead of using :func:`aud.Sound.limit` and :func:`aud.Sound.join`
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we simply add the sound to the sequence.
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.. code-block:: python
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entry = sequence.add(note, position, position + length, 0)
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The entry returned from the :func:`aud.Sequence.add`
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function is an object of the :class:`aud.SequenceEntry` class.
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We can use this entry to mute the note in case it's actually a pause.
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.. code-block:: python
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if char == 'p':
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entry.muted = True
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Lastly we have to update our position variable.
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.. code-block:: python
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position += length
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Now in **tetris2.py** we used the :data:`aud.SequenceEntry.muted`
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property to show how the :class:`aud.SequenceEntry` class can be used,
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but it would actually be smarter to not even create a note for pauses and just skip them.
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You can try to implement this as an exercise and then check out the solution in **tetris3.py**.
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Conclusion
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----------
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We introduced all five currently available classes in the audaspace Python API.
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Of course all classes offer a lot more functions than have been used in these demo applications,
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check out the specific class documentation for more details.
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