effect_position.c

SDL_mixer 是一个基于 SDL 的混音器

		    case 2:
            		f = (_Eff_build_volume_table_u8()) ? _Eff_position_table_u8 :
                                                 		_Eff_position_u8;
	    		break;
	    	    case 4:
                        f = _Eff_position_u8_c4;
	    		break;
	    	    case 6:
                        f = _Eff_position_u8_c6;
	    		break;
	    }
            break;

        case AUDIO_S8:
	    switch (channels) {
		    case 1:
		    case 2:
            		f = (_Eff_build_volume_table_s8()) ? _Eff_position_table_s8 :
                                                 		_Eff_position_s8;
	    		break;
	    	    case 4:
                        f = _Eff_position_s8_c4;
	    		break;
	    	    case 6:
                        f = _Eff_position_s8_c6;
	    		break;
	    }
            break;

        case AUDIO_U16LSB:
	    switch (channels) {
		    case 1:
		    case 2:
            		f = _Eff_position_u16lsb;
	    		break;
	    	    case 4:
            		f = _Eff_position_u16lsb_c4;
	    		break;
	    	    case 6:
            		f = _Eff_position_u16lsb_c6;
	    		break;
	    }
            break;

        case AUDIO_S16LSB:
	    switch (channels) {
		    case 1:
		    case 2:
            		f = _Eff_position_s16lsb;
	    		break;
	    	    case 4:
            		f = _Eff_position_s16lsb_c4;
	    		break;
	    	    case 6:
            		f = _Eff_position_s16lsb_c6;
	    		break;
	    }
            break;

        case AUDIO_U16MSB:
	    switch (channels) {
		    case 1:
		    case 2:
            		f = _Eff_position_u16msb;
	    		break;
	    	    case 4:
            		f = _Eff_position_u16msb_c4;
	    		break;
	    	    case 6:
            		f = _Eff_position_u16msb_c6;
	    		break;
	    }
            break;

        case AUDIO_S16MSB:
	    switch (channels) {
		    case 1:
		    case 2:
            		f = _Eff_position_s16msb;
	    		break;
	    	    case 4:
            		f = _Eff_position_s16msb_c4;
	    		break;
	    	    case 6:
            		f = _Eff_position_s16msb_c6;
	    		break;
	    }
            break;

        default:
            Mix_SetError("Unsupported audio format");
    }

    return(f);
}

static Uint8 speaker_amplitude[6];

static void set_amplitudes(int channels, int angle, int room_angle)
{
    int left = 255, right = 255;
    int left_rear = 255, right_rear = 255, center = 255;

        /* unwind the angle...it'll be between 0 and 359. */
    while (angle >= 360) angle -= 360;
    while (angle < 0) angle += 360;

    if (channels == 2)
    {
        /*
         * We only attenuate by position if the angle falls on the far side
         *  of center; That is, an angle that's due north would not attenuate
         *  either channel. Due west attenuates the right channel to 0.0, and
         *  due east attenuates the left channel to 0.0. Slightly east of
         *  center attenuates the left channel a little, and the right channel
         *  not at all. I think of this as occlusion by one's own head.  :)
         *
         *   ...so, we split our angle circle into four quadrants...
         */
        if (angle < 90) {
            left = 255 - ((int) (255.0f * (((float) angle) / 89.0f)));
        } else if (angle < 180) {
            left = (int) (255.0f * (((float) (angle - 90)) / 89.0f));
        } else if (angle < 270) {
            right = 255 - ((int) (255.0f * (((float) (angle - 180)) / 89.0f)));
        } else {
            right = (int) (255.0f * (((float) (angle - 270)) / 89.0f));
        }
    }

    if (channels == 4 || channels == 6)
    {
        /*
         *  An angle that's due north does not attenuate the center channel.
         *  An angle in the first quadrant, 0-90, does not attenuate the RF.
         *
         *   ...so, we split our angle circle into 8 ...
	 *
	 *             CE
	 *             0
	 *     LF      |         RF
	 *             |
	 *  270<-------|----------->90
	 *             |
	 *     LR      |         RR
	 *            180
	 *   
         */
        if (angle < 45) {
            left = ((int) (255.0f * (((float) (180 - angle)) / 179.0f)));
            left_rear = 255 - ((int) (255.0f * (((float) (angle + 45)) / 89.0f)));
            right_rear = 255 - ((int) (255.0f * (((float) (90 - angle)) / 179.0f)));
        } else if (angle < 90) {
            center = ((int) (255.0f * (((float) (225 - angle)) / 179.0f)));
            left = ((int) (255.0f * (((float) (180 - angle)) / 179.0f)));
            left_rear = 255 - ((int) (255.0f * (((float) (135 - angle)) / 89.0f)));
            right_rear = ((int) (255.0f * (((float) (90 + angle)) / 179.0f)));
        } else if (angle < 135) {
            center = ((int) (255.0f * (((float) (225 - angle)) / 179.0f)));
            left = 255 - ((int) (255.0f * (((float) (angle - 45)) / 89.0f)));
            right = ((int) (255.0f * (((float) (270 - angle)) / 179.0f)));
            left_rear = ((int) (255.0f * (((float) (angle)) / 179.0f)));
        } else if (angle < 180) {
            center = 255 - ((int) (255.0f * (((float) (angle - 90)) / 89.0f)));
            left = 255 - ((int) (255.0f * (((float) (225 - angle)) / 89.0f)));
            right = ((int) (255.0f * (((float) (270 - angle)) / 179.0f)));
            left_rear = ((int) (255.0f * (((float) (angle)) / 179.0f)));
        } else if (angle < 225) {
            center = 255 - ((int) (255.0f * (((float) (270 - angle)) / 89.0f)));
            left = ((int) (255.0f * (((float) (angle - 90)) / 179.0f)));
            right = 255 - ((int) (255.0f * (((float) (angle - 135)) / 89.0f)));
            right_rear = ((int) (255.0f * (((float) (360 - angle)) / 179.0f)));
        } else if (angle < 270) {
            center = ((int) (255.0f * (((float) (angle - 135)) / 179.0f)));
            left = ((int) (255.0f * (((float) (angle - 90)) / 179.0f)));
            right = 255 - ((int) (255.0f * (((float) (315 - angle)) / 89.0f)));
            right_rear = ((int) (255.0f * (((float) (360 - angle)) / 179.0f)));
        } else if (angle < 315) {
            center = ((int) (255.0f * (((float) (angle - 135)) / 179.0f)));
            right = ((int) (255.0f * (((float) (angle - 180)) / 179.0f)));
            left_rear = ((int) (255.0f * (((float) (450 - angle)) / 179.0f)));
            right_rear = 255 - ((int) (255.0f * (((float) (angle - 225)) / 89.0f)));
        } else {
            right = ((int) (255.0f * (((float) (angle - 180)) / 179.0f)));
            left_rear = ((int) (255.0f * (((float) (450 - angle)) / 179.0f)));
            right_rear = 255 - ((int) (255.0f * (((float) (405 - angle)) / 89.0f)));
        }
    }

    if (left < 0) left = 0; if (left > 255) left = 255;
    if (right < 0) right = 0; if (right > 255) right = 255;
    if (left_rear < 0) left_rear = 0; if (left_rear > 255) left_rear = 255;
    if (right_rear < 0) right_rear = 0; if (right_rear > 255) right_rear = 255;
    if (center < 0) center = 0; if (center > 255) center = 255;

    if (room_angle == 90) {
    	speaker_amplitude[0] = (Uint8)left_rear;
    	speaker_amplitude[1] = (Uint8)left;
    	speaker_amplitude[2] = (Uint8)right_rear;
    	speaker_amplitude[3] = (Uint8)right;
    }
    else if (room_angle == 180) {
	if (channels == 2) {
    	    speaker_amplitude[0] = (Uint8)right;
    	    speaker_amplitude[1] = (Uint8)left;
	}
	else {
    	    speaker_amplitude[0] = (Uint8)right_rear;
    	    speaker_amplitude[1] = (Uint8)left_rear;
    	    speaker_amplitude[2] = (Uint8)right;
    	    speaker_amplitude[3] = (Uint8)left;
	}
    }
    else if (room_angle == 270) {
    	speaker_amplitude[0] = (Uint8)right;
    	speaker_amplitude[1] = (Uint8)right_rear;
    	speaker_amplitude[2] = (Uint8)left;
    	speaker_amplitude[3] = (Uint8)left_rear;
    }
    else {
    	speaker_amplitude[0] = (Uint8)left;
    	speaker_amplitude[1] = (Uint8)right;
    	speaker_amplitude[2] = (Uint8)left_rear;
    	speaker_amplitude[3] = (Uint8)right_rear;
    }
    speaker_amplitude[4] = (Uint8)center;
    speaker_amplitude[5] = 255;
}

int Mix_SetPosition(int channel, Sint16 angle, Uint8 distance);

int Mix_SetPanning(int channel, Uint8 left, Uint8 right)
{
    Mix_EffectFunc_t f = NULL;
    int channels;
    Uint16 format;
    position_args *args = NULL;
    Mix_QuerySpec(NULL, &format, &channels);

    if (channels != 2 && channels != 4 && channels != 6)    /* it's a no-op; we call that successful. */
        return(1);

    if (channels > 2) {
    	/* left = 255 =>  angle = -90;  left = 0 => angle = +89 */
    	int angle = (int)left;
    	angle = 127 - angle;
	angle = -angle;
    	angle = angle * 90 / 128; /* Make it larger for more effect? */
	return( Mix_SetPosition(channel, angle, 0) );
    }

    f = get_position_effect_func(format, channels);
    if (f == NULL)
        return(0);

    args = get_position_arg(channel);
    if (!args)
        return(0);

        /* it's a no-op; unregister the effect, if it's registered. */
    if ((args->distance_u8 == 255) && (left == 255) &&
        (right == 255) && (args->in_use))
    {
        return(Mix_UnregisterEffect(channel, f));
    }

    args->left_u8 = left;
    args->left_f = ((float) left) / 255.0f;
    args->right_u8 = right;
    args->right_f = ((float) right) / 255.0f;
    args->room_angle = 0;

    if (!args->in_use) {
        args->in_use = 1;
        return(Mix_RegisterEffect(channel, f, _Eff_PositionDone, (void *) args));
    }

    return(1);
}


int Mix_SetDistance(int channel, Uint8 distance)
{
    Mix_EffectFunc_t f = NULL;
    Uint16 format;
    position_args *args = NULL;
    int channels;

    Mix_QuerySpec(NULL, &format, &channels);
    f = get_position_effect_func(format, channels);
    if (f == NULL)
        return(0);

    args = get_position_arg(channel);
    if (!args)
        return(0);

    distance = 255 - distance;  /* flip it to our scale. */

        /* it's a no-op; unregister the effect, if it's registered. */
    if ((distance == 255) && (args->left_u8 == 255) &&
        (args->right_u8 == 255) && (args->in_use))
    {
        return(Mix_UnregisterEffect(channel, f));
    }

    args->distance_u8 = distance;
    args->distance_f = ((float) distance) / 255.0f;
    if (!args->in_use) {
        args->in_use = 1;
        return(Mix_RegisterEffect(channel, f, _Eff_PositionDone, (void *) args));
    }

    return(1);
}


int Mix_SetPosition(int channel, Sint16 angle, Uint8 distance)
{
    Mix_EffectFunc_t f = NULL;
    Uint16 format;
    int channels;
    position_args *args = NULL;
    Sint16 room_angle;

    Mix_QuerySpec(NULL, &format, &channels);
    f = get_position_effect_func(format, channels);
    if (f == NULL)
        return(0);

        /* unwind the angle...it'll be between 0 and 359. */
    while (angle >= 360) angle -= 360;
    while (angle < 0) angle += 360;

    args = get_position_arg(channel);
    if (!args)
        return(0);

        /* it's a no-op; unregister the effect, if it's registered. */
    if ((!distance) && (!angle) && (args->in_use))
        return(Mix_UnregisterEffect(channel, f));

    if (channels == 2)
    {
	if (angle > 180)
		room_angle = 180; /* exchange left and right channels */
	else room_angle = 0;
    }

    if (channels == 4 || channels == 6)
    {
	if (angle > 315) room_angle = 0;
	else if (angle > 225) room_angle = 270;
	else if (angle > 135) room_angle = 180;
	else if (angle > 45) room_angle = 90;
	else room_angle = 0;
    }


    distance = 255 - distance;  /* flip it to scale Mix_SetDistance() uses. */

    set_amplitudes(channels, angle, room_angle);

    args->left_u8 = speaker_amplitude[0];
    args->left_f = ((float) speaker_amplitude[0]) / 255.0f;
    args->right_u8 = speaker_amplitude[1];
    args->right_f = ((float) speaker_amplitude[1]) / 255.0f;
    args->left_rear_u8 = speaker_amplitude[2];
    args->left_rear_f = ((float) speaker_amplitude[2]) / 255.0f;
    args->right_rear_u8 = speaker_amplitude[3];
    args->right_rear_f = ((float) speaker_amplitude[3]) / 255.0f;
    args->center_u8 = speaker_amplitude[4];
    args->center_f = ((float) speaker_amplitude[4]) / 255.0f;
    args->lfe_u8 = 255;
    args->lfe_f = 255.0f;
    args->distance_u8 = distance;
    args->distance_f = ((float) distance) / 255.0f;
    args->room_angle = room_angle;
    if (!args->in_use) {
        args->in_use = 1;
        return(Mix_RegisterEffect(channel, f, _Eff_PositionDone, (void *) args));
    }

    return(1);
}


/* end of effects_position.c ... */