vlc/modules/visualization/visual/window.c

/*****************************************************************************
 * window.c : Implementation of FFT window routines
 *****************************************************************************
 * Copyright (C) 2014 Ronald Wright
 * $Id$
 *
 * Author: Ronald Wright <logiconcepts819@gmail.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
 *****************************************************************************/

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include <math.h>
#include "window.h"
#include "window_presets.h"

#include <assert.h>

/* Flat top window coefficients */
#define FT_A0 1.000f
#define FT_A1 1.930f
#define FT_A2 1.290f
#define FT_A3 0.388f
#define FT_A4 0.028f

/* Blackman-Harris window coefficients */
#define BH_A0 0.35875f
#define BH_A1 0.48829f
#define BH_A2 0.14128f
#define BH_A3 0.01168f

/*
 * The modified Bessel function I0(x).  See Chapter 6 of the "Numerical Recipes
 * in C: The Art of Scientific Computing" book at
 * http://www.aip.de/groups/soe/local/numres/bookcpdf/c6-6.pdf
 */
static float bessi0( float x )
{
    float ax, ans;
    double y; /* Accumulate polynomials in double precision. */
    if( ( ax = fabsf( x ) ) < 3.75f ) /* Polynomial fit. */
    {
        y = x / 3.75;
        y *= y;
        ans = 1.0 + y * ( 3.5156229 + y * ( 3.0899424 + y * ( 1.2067492
                  + y * ( 0.2659732 + y * ( 0.360768e-1
                  + y * 0.45813e-2 ) ) ) ) );
    }
    else
    {
        y = 3.75 / ax;
        ans = ( exp( ax ) / sqrt( ax ) ) * ( 0.39894228 + y * ( 0.1328592e-1
            + y * ( 0.225319e-2 + y * ( -0.157565e-2 + y * ( 0.916281e-2
            + y * ( -0.2057706e-1 + y * ( 0.2635537e-1 + y * ( -0.1647633e-1
            + y * 0.392377e-2 ) ) ) ) ) ) ) );
    }
    return ans;
}

/*
 * Obtain the window type from the window type variable.
 */
void window_get_param( vlc_object_t * p_aout, window_param * p_param )
{
    /* Fetch Kaiser parameter */
    p_param->f_kaiser_alpha = var_InheritFloat( p_aout, "effect-kaiser-param" );

    /* Fetch window type */
    char * psz_preset = var_InheritString( p_aout, "effect-fft-window" );
    if( !psz_preset )
    {
        goto no_preset;
    }

    for( int i = 0; i < NB_WINDOWS; i++ )
    {
        if( !strcasecmp( psz_preset, window_list[i] ) )
        {
            p_param->wind_type = i;
            return;
        }
    }

no_preset:
    msg_Warn( p_aout, "No matching window preset found; using rectangular "
                      "window (i.e. no window)" );
    p_param->wind_type = NONE;
}

/*
 * Initialization routine - sets up a lookup table for scaling a sample of data
 * by window data.  If the lookup table is successfully allocated, its memory
 * location and its specified size are stored at the specified memory location
 * of the internal context.
 * Returns true if initialization succeeded and returns false otherwise.
 * The internal context should be freed when it is finished with, by
 * window_close().
 */
bool window_init( int i_buffer_size, window_param * p_param,
                  window_context * p_ctx )
{
    float * pf_table = NULL;
    window_type wind_type = p_param->wind_type;

    if( wind_type != HANN && wind_type != FLATTOP
                          && wind_type != BLACKMANHARRIS
                          && wind_type != KAISER )
    {
        /* Assume a rectangular window (i.e. no window) */
        i_buffer_size = 0;
        goto exit;
    }

    pf_table = malloc( i_buffer_size * sizeof( *pf_table ) );
    if( !pf_table )
    {
        /* Memory allocation failed */
        return false;
    }

    int i_buffer_size_minus_1 = i_buffer_size - 1;
    switch( wind_type )
    {
    case HANN:
        /* Hann window */
        for( int i = 0; i < i_buffer_size; i++ )
        {
            float f_val = (float) i / (float) i_buffer_size_minus_1;
            pf_table[i] = 0.5f - 0.5f * cosf( 2.0f * (float) M_PI * f_val );
        }
        break;
    case FLATTOP:
        /* Flat top window */
        for( int i = 0; i < i_buffer_size; i++ )
        {
            float f_val = (float) i / (float) i_buffer_size_minus_1;
            pf_table[i] = FT_A0
                        - FT_A1 * cosf( 2.0f * (float) M_PI * f_val )
                        + FT_A2 * cosf( 4.0f * (float) M_PI * f_val )
                        - FT_A3 * cosf( 6.0f * (float) M_PI * f_val )
                        + FT_A4 * cosf( 8.0f * (float) M_PI * f_val );
        }
        break;
    case BLACKMANHARRIS:
        /* Blackman-Harris window */
        for( int i = 0; i < i_buffer_size; i++ )
        {
            float f_val = (float) i / (float) i_buffer_size_minus_1;
            pf_table[i] = BH_A0
                        - BH_A1 * cosf( 2.0f * (float) M_PI * f_val )
                        + BH_A2 * cosf( 4.0f * (float) M_PI * f_val )
                        - BH_A3 * cosf( 6.0f * (float) M_PI * f_val );
        }
        break;
    case KAISER:
    {
        /* Kaiser window */
        float f_pialph = (float) M_PI * p_param->f_kaiser_alpha;
        float f_bessi0_pialph = bessi0( f_pialph );
        for( int i = 0; i < i_buffer_size; i++ )
        {
            float f_val = (float) i / (float) i_buffer_size_minus_1;
            float f_term_to_square = 2.0f * f_val - 1.0f;
            float f_sqd_term = f_term_to_square * f_term_to_square;
            float f_sqr_term = sqrtf( 1.0f - f_sqd_term );
            pf_table[i] = bessi0( f_pialph * f_sqr_term ) / f_bessi0_pialph;
        }
        break;
    }
    default:
        /* We should not reach here */
        vlc_assert_unreachable();
        break;
    }

exit:
    p_ctx->pf_window_table = pf_table;
    p_ctx->i_buffer_size = i_buffer_size;
    return true;
}

/*
 * Perform an in-place scaling of the input buffer by the window data
 * referenced from the specified context.
 */
void window_scale_in_place( int16_t * p_buffer, window_context * p_ctx )
{
    for( int i = 0; i < p_ctx->i_buffer_size; i++ )
    {
        p_buffer[i] *= p_ctx->pf_window_table[i];
    }
}

/*
 * Free the context.
 */
void window_close( window_context * p_ctx )
{
    if( p_ctx->pf_window_table )
    {
        free( p_ctx->pf_window_table );
        p_ctx->pf_window_table = NULL;
        p_ctx->i_buffer_size = 0;
    }
}