[openal] example code request for Echo and other effects?

[Chris Robinson]

On Fri, 14 Aug 2020 14:44:21 +0300
Sean <s.tolstoyevski at gmail.com> wrote:

> Hi all,
> 
> I can't learn anything from the sample review. Since I am actively 
> coding in Python, I find it very difficult to understand OpenAL's C
> API.
> 
> Can you send me sample code for effects like Echo?
> 
> I read the reverb from example.
> But I could not find any other example of effect.

Hi.

Using the echo effect is very similar to using the reverb effect. Given
the LoadEffect function in examples/alreverb.c, it can be easily changed
to use the echo effect:

static ALuint LoadEffect(void)
{
    ALuint effect = 0;
    ALenum err;

    /* Create the effect object and set the echo type. */
    alGenEffects(1, &effect);
    alEffecti(effect, AL_EFFECT_TYPE, AL_EFFECT_ECHO);

    /* Check if an error occured, and clean up if so. */
    err = alGetError();
    if(err != AL_NO_ERROR)
    {
        fprintf(stderr, "OpenAL error: %s\n", alGetString(err));
        if(alIsEffect(effect))
            alDeleteEffects(1, &effect);
        return 0;
    }

    return effect;
}

That will create an echo effect with the default parameters. To change
the echo parameters, set them after setting the echo type:

alEffecti(effect, AL_EFFECT_TYPE, AL_EFFECT_ECHO);
/* Note the 'f' on these functions, not 'i' like above */
alEffectf(effect, AL_ECHO_DELAY, ...); /* 0.0f ... 0.207f */
alEffectf(effect, AL_ECHO_LRDELAY ...); /* 0.0f ... 0.404f */
alEffectf(effect, AL_ECHO_DAMPING ...); /* 0.0f ... 0.99f */
alEffectf(effect, AL_ECHO_FEEDBACK ...); /* 0.0f ... 1.0f */
alEffectf(effect, AL_ECHO_SPREAD ...); /* -1.0f ... 1.0f */

I don't use Python myself so unfortunately I can't make a Python
example, but if you were able to work through the alreverb example,
it's not very different. If you still have any questions, feel free to
ask.