Re: Question about OpenAl Versions

On Monday, November 15, 2010 7:34:21 pm Bruce Clay wrote:
> if (deviceName.length() > 0)
> {
> 	mCurrCaptureDevice = alcCaptureOpenDevice (deviceName.c_str(),
> sampleRate, audioFormat, sampleBufSize);
> }
> else
> {
> 	mCurrCaptureDevice = alcCaptureOpenDevice (NULL, sampleRate,
> audioFormat, sampleBufSize);
> }
> 
> int error = alGetError();

This won't do what you expect. alGetError only returns the last error from the 
current context, and opening a capture device doesn't use a context. The way 
to check for an error would be to look for a NULL return value, then use 
alcGetError(NULL) to get the error code.

> formatChunk.format = WAVE_FORMAT_PCM;
> formatChunk.numChannels = numChannels;
> formatChunk.samplesPerSec = sampleRate;
> formatChunk.avgBytesPerSec = sampleRate * numChannels * bitsPerSample / 8;
> formatChunk.blockAlign = numChannels * bitsPerSample / 8;
> formatChunk.bitsPerSample = bitsPerSample;
> 
> fwrite(FORMAT_TAG, strlen(FORMAT_TAG), 1, fdes);
> 
> fieldLen = sizeof(formatChunk);
> 
> fwrite(&fieldLen, sizeof(fieldLen), 1, fdes);
> 
> fwrite(&formatChunk, fieldLen, 1, fdes);

It's not a good idea to write whole structs and integers to a file, since it 
assumes a particular endianess and structure padding, which may not always be 
true. It's better to read/write each field separately, using wrappers so 16- 
and 32-bit values are properly handled.

> unsigned long currPos = ftell(fdes);
> 
> chunkSize = currPos - mStartChunkPos;
> 
> fseek(fdes, mStartChunkPos + sizeof(chunkSize), SEEK_SET);
> 
> fwrite(&chunkSize, chunkSize, 1, fdes);

That last bit doesn't look right. The chunk size is only 4 bytes, not 
'chunkSize' bytes. But again, it's better to use dedicated functions to write 
16- and 32-bit values, to help avoid problems like this:

size_t fwrite32le(unsigned int value, FILE *fdes)
{
    unsigned char buf[4] = {
        value&0xff, (value>>8)&0xff, (value>>16)&0xff, (value>>24)&0xff
    };
    return fwrite(buf, 4, 1, fdes);
}

size_t fwrite16le(unsigned short value, FILE *fdes)
{
    unsigned char buf[2] = {
        value&0xff, (value>>8)&0xff
    };
    return fwrite(buf, 2, 1, fdes);
}
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