DevMaster.net Game Development

From 10be763d626885040778e82ed8e91f3ad283b697 Mon Sep 17 00:00:00 2001 From: athomas Date: Sun, 29 Jun 2003 04:31:27 +0000 Subject: check-in of lesson 4 git-svn-id: file:///home/mbien/NetBeansProjects/JOGAMP/joal-sync/svn-server-sync-demos/joal-demos/trunk@26 235fdd13-0e8c-4fed-b5ee-0a390d04b286 --- www/devmaster/lesson4.html | 165 +++++++++++++++++++++++++++++++++++++++++++++ www/index.html | 4 +- 2 files changed, 168 insertions(+), 1 deletion(-) create mode 100644 www/devmaster/lesson4.html (limited to 'www') diff --git a/www/devmaster/lesson4.html b/www/devmaster/lesson4.html new file mode 100644 index 0000000..39559c3 --- /dev/null +++ b/www/devmaster/lesson4.html @@ -0,0 +1,165 @@ + + + + DevMaster.net Game Development + + +

+ +

+ + + + + + + +
+OpenAL Tutorials from DevMaster.net. Reprinted with Permission.
+
+ + + + + + +

OpenAL + Tutorials

DevMaster.net

+ +

A Closer Look at ALC

Lesson 4

Author: Jesse + Maurais
+ Adapted for Java by: Athomas + Goldberg

Up until now we have been letting Alut do all the real tricky + stuff for us. For example handling the audio devices. It's really nice that + the Alut library is there to provide this functionality, but any smart coder + will want to know exactly what their doing. We may want to, at some point, use + the Alc directly. In this tutorial we will expose the Alc layer and take a look + at how to handle the devices on our own.

+ALFactory.initialize();
+ALC alc = ALFactory.getALC();
+
+
+String deviceName = "DirectSound3D";
+
+ALC.Device device = alc.alcOpenDevice(deviceName);
+

So what is an Alc device? Try to think of it in terms of a + resource. OpenAL grabs a handle to the hardware being used, which must in turn + be shared with the entire system. A device can be of a specific implementation + as well, as in this case where we are using DirectSound as the audio device. + This code grabs a handle to the hardware device and readies it to be used by + the application. Eventually we should see more devices made for specific soundcards.

Passing null + to 'alcOpenDevice' is a perfectly valid argument. It forces the Alc to use a + default device.

+ALC.Context context = alc.alcCreateContext(device, null);
+alc.alcMakeContextCurrent(context);
+

What is an Alc context? OpenGL coders will recall that there + was rendering contexts used by OpenGL that controlled the state management across + different windows. An 'HGLRC' as they are called could be created several times + to enable multiple rendering windows. And different rendering states for each + context could be achieved. An Alc context works on the same principal. First + we tell it which device to use (which we have already created), then we make + that context current. In theory you could create multiple rendering contexts + for different windows, and set the state variables differently and have it work + just fine. Although the term "rendering context" usually applies to + a visual rendering, this is the term preferred in the sdk docs and should be + the term used.

You may notice too that the second parameter in 'alcCreateContext' + has been set to null. The OpenAL + sdk from Creative Labs defines the following variables which are optional flags + to that parameter.

ALC_FREQUENCY
ALC_REFRESH
ALC_SYNC

If you were to create multiple contexts you could make them + interchangeable by making a call to 'alcMakeContextCurrent'. Sending NULL to + 'alcMakeContextCurrent' is also a perfectly valid argument. It will prevent + processing of any audio data. Be aware that even if you have multiple rendering + contexts, you can only have one current at a time, and when your application + needs to use two contexts interchangeably you must be the one to make sure the + appropriate context is current. And if you do decide to do this, then there + may be times when you want to know exactly which context is current without + going through a big check.

ALC.Context curContext = alc.alcGetCurrentContext();
+

Once you have your context you can also obtain the device in use by that context.

ALC.Device curDevice = alc.alcGetContextsDevice(curContext);
+

Above we used the context we retrieved to find out which device + it was using. There is also one other cool feature that was built into Alc for + handling contexts.

alc.alcSuspendContext(context);
+// Processing has been suspended to context.
+
+alc.alcProcessContext(context);
+// Processing has been re-enabled to context.
+

What we have done above was stop, and then resume processing + of audio data to the context. When processing has been suspended, no sound will + be generated from data sent through that context. A further note on the rendering + context: the OpenAL 1.0 spec does imply, but does not explicitly say, that sources + and buffers may be used across contexts. The "lifetime" of a source + or buffer during the application, is said to be valid as long as the source + and buffer id is valid (i.e. they have not been deleted).

alc.alcMakeContextCurrent(null);
+alc.alcDestroyContext(context);
+alc.alcCloseDevice(device);
+

And that is how we clean up. The current context is defaulted + to null, the context we created + is released, and the handle to the device is given back to the system resources. + There is but a few more Alc functions we have not yet covered.

public int alcGetError();
+
+public boolean alcIsExtensionPresent(ALC.Device device, String extName);
+
+public int alcGetEnumValue(ALC.Device device, String enumName);
+
+public String alcGetString(ALC.Device device, int token);
+
+public void alcGetIntegerv(ALC.Device device, int token, int size, int[] dest);
+

It may be pretty obvious to you what these do, but lets humour + ourselves and have a closer look. First we have 'alcGetError' which is just + like 'alGetError' but will return Alc errors. The next two functions are for + querying Alc extensions. This was just the creators planning ahead, as there + are no Alc extensions either. The last function, 'alcGetInteger', will return + the Alc version when passed 'ALC_MAJOR_VERSION' or 'ALC_MINOR_VERSION'.

The function 'alcGetString' is pretty cool. It can take any of the following + three parameters to 'token':

ALC_DEFAULT_DEVICE_SPECIFIER
ALC_DEVICE_SPECIFIER
ALC_EXTENSIONS

The first will return the device string which your OpenAL implementation + will prefer you to use. In current OpenAL this should be "DirectSound3D", + like we used above. The second token will return a list of specifiers, but in + current OpenAL will only return "DirectSound" (without the "3D" + for some reason). The last will return a list of Alc extensions, of which none + exist yet.

Well that's most of Alc for you. I hope it gave you a better + understanding of how OpenAL interacts with the operation system. You might try + writing your own initialization routines so you can cast off Alut altogether. + Either way have fun with it.

+ + + + + +

+ Contact us if you + want to write for us or for any comments, suggestions, or feedback.

+ + \ No newline at end of file diff --git a/www/index.html b/www/index.html index 76b55e3..c3fdf31 100644 --- a/www/index.html +++ b/www/index.html @@ -98,8 +98,10 @@ Static Source

lesson 2: Looping and Fadeaway

lesson 3: Multiple +

lesson 3: Multiple Sources

lesson 4: A Closer + Look at the ALC

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