/*****************************************************************************
 * gradient.c : Gradient and edge detection video effects plugin for vlc
 *****************************************************************************
 * Copyright (C) 2000-2008 VLC authors and VideoLAN
 * $Id: 7f9f000337bdcac385f56b51b0e7411308acad9a $
 *
 * Authors: Samuel Hocevar <sam@zoy.org>
 *          Antoine Cellerier <dionoea -at- videolan -dot- org>
 *
 * 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.
 *****************************************************************************/

/*****************************************************************************
 * Preamble
 *****************************************************************************/

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

#include <math.h>                                            /* sin(), cos() */

#include <vlc_common.h>
#include <vlc_plugin.h>
#include <vlc_sout.h>
#include <vlc_filter.h>
#include <vlc_picture.h>
#include "filter_picture.h"

enum { GRADIENT, EDGE, HOUGH };

/*****************************************************************************
 * Local prototypes
 *****************************************************************************/
static int  Create    ( vlc_object_t * );
static void Destroy   ( vlc_object_t * );

static picture_t *Filter( filter_t *, picture_t * );
static int GradientCallback( vlc_object_t *, char const *,
                             vlc_value_t, vlc_value_t,
                             void * );

static void FilterGradient( filter_t *, picture_t *, picture_t * );
static void FilterEdge    ( filter_t *, picture_t *, picture_t * );
static void FilterHough   ( filter_t *, picture_t *, picture_t * );

/*****************************************************************************
 * Module descriptor
 *****************************************************************************/
#define MODE_TEXT N_("Distort mode")
#define MODE_LONGTEXT N_("Distort mode, one of \"gradient\", \"edge\" and \"hough\".")

#define GRADIENT_TEXT N_("Gradient image type")
#define GRADIENT_LONGTEXT N_("Gradient image type (0 or 1). 0 will " \
        "turn the image to white while 1 will keep colors." )

#define CARTOON_TEXT N_("Apply cartoon effect")
#define CARTOON_LONGTEXT N_("Apply cartoon effect. It is only used by " \
    "\"gradient\" and \"edge\".")

#define GRADIENT_HELP N_("Apply color gradient or edge detection effects")

static const char *const mode_list[] = { "gradient", "edge", "hough" };
static const char *const mode_list_text[] = { N_("Gradient"), N_("Edge"), N_("Hough") };

#define FILTER_PREFIX "gradient-"

vlc_module_begin ()
    set_description( N_("Gradient video filter") )
    set_shortname( N_( "Gradient" ))
    set_help(GRADIENT_HELP)
    set_capability( "video filter", 0 )
    set_category( CAT_VIDEO )
    set_subcategory( SUBCAT_VIDEO_VFILTER )

    add_string( FILTER_PREFIX "mode", "gradient",
                MODE_TEXT, MODE_LONGTEXT, false )
        change_string_list( mode_list, mode_list_text )

    add_integer_with_range( FILTER_PREFIX "type", 0, 0, 1,
                GRADIENT_TEXT, GRADIENT_LONGTEXT, false )
    add_bool( FILTER_PREFIX "cartoon", true,
                CARTOON_TEXT, CARTOON_LONGTEXT, false )

    add_shortcut( "gradient" )
    set_callbacks( Create, Destroy )
vlc_module_end ()

static const char *const ppsz_filter_options[] = {
    "mode", "type", "cartoon", NULL
};

/*****************************************************************************
 * filter_sys_t: Distort video output method descriptor
 *****************************************************************************
 * This structure is part of the video output thread descriptor.
 * It describes the Distort specific properties of an output thread.
 *****************************************************************************/
struct filter_sys_t
{
    vlc_mutex_t lock;
    int i_mode;

    /* For the gradient mode */
    int i_gradient_type;
    bool b_cartoon;

    uint32_t *p_buf32;
    uint32_t *p_buf32_bis;
    uint8_t *p_buf8;

    /* For hough mode */
    int *p_pre_hough;
};

/*****************************************************************************
 * Create: allocates Distort video thread output method
 *****************************************************************************
 * This function allocates and initializes a Distort vout method.
 *****************************************************************************/
static int Create( vlc_object_t *p_this )
{
    filter_t *p_filter = (filter_t *)p_this;
    char *psz_method;

    switch( p_filter->fmt_in.video.i_chroma )
    {
        CASE_PLANAR_YUV
            break;

        default:
             msg_Err( p_filter, "Unsupported input chroma (%4.4s)",
                      (char*)&(p_filter->fmt_in.video.i_chroma) );
            return VLC_EGENERIC;
    }

    /* Allocate structure */
    p_filter->p_sys = malloc( sizeof( filter_sys_t ) );
    if( p_filter->p_sys == NULL )
        return VLC_ENOMEM;

    p_filter->pf_video_filter = Filter;

    p_filter->p_sys->p_pre_hough = NULL;

    config_ChainParse( p_filter, FILTER_PREFIX, ppsz_filter_options,
                   p_filter->p_cfg );

    if( !(psz_method =
        var_CreateGetNonEmptyStringCommand( p_filter, FILTER_PREFIX "mode" )) )
    {
        msg_Err( p_filter, "configuration variable "
                 FILTER_PREFIX "mode empty" );
        p_filter->p_sys->i_mode = GRADIENT;
    }
    else
    {
        if( !strcmp( psz_method, "gradient" ) )
        {
            p_filter->p_sys->i_mode = GRADIENT;
        }
        else if( !strcmp( psz_method, "edge" ) )
        {
            p_filter->p_sys->i_mode = EDGE;
        }
        else if( !strcmp( psz_method, "hough" ) )
        {
            p_filter->p_sys->i_mode = HOUGH;
        }
        else
        {
            msg_Err( p_filter, "no valid gradient mode provided (%s)", psz_method );
            p_filter->p_sys->i_mode = GRADIENT;
        }
    }
    free( psz_method );

    p_filter->p_sys->i_gradient_type =
        var_CreateGetIntegerCommand( p_filter, FILTER_PREFIX "type" );
    p_filter->p_sys->b_cartoon =
        var_CreateGetBoolCommand( p_filter, FILTER_PREFIX "cartoon" );

    vlc_mutex_init( &p_filter->p_sys->lock );
    var_AddCallback( p_filter, FILTER_PREFIX "mode",
                     GradientCallback, p_filter->p_sys );
    var_AddCallback( p_filter, FILTER_PREFIX "type",
                     GradientCallback, p_filter->p_sys );
    var_AddCallback( p_filter, FILTER_PREFIX "cartoon",
                     GradientCallback, p_filter->p_sys );

    p_filter->p_sys->p_buf32 = NULL;
    p_filter->p_sys->p_buf32_bis = NULL;
    p_filter->p_sys->p_buf8 = NULL;

    return VLC_SUCCESS;
}

/*****************************************************************************
 * Destroy: destroy Distort video thread output method
 *****************************************************************************
 * Terminate an output method created by DistortCreateOutputMethod
 *****************************************************************************/
static void Destroy( vlc_object_t *p_this )
{
    filter_t *p_filter = (filter_t *)p_this;
    filter_sys_t *p_sys = p_filter->p_sys;

    var_DelCallback( p_filter, FILTER_PREFIX "mode",
                     GradientCallback, p_sys );
    var_DelCallback( p_filter, FILTER_PREFIX "type",
                     GradientCallback, p_sys );
    var_DelCallback( p_filter, FILTER_PREFIX "cartoon",
                     GradientCallback, p_sys );
    vlc_mutex_destroy( &p_sys->lock );

    free( p_sys->p_buf32 );
    free( p_sys->p_buf32_bis );
    free( p_sys->p_buf8 );
    free( p_sys->p_pre_hough );

    free( p_sys );
}

/*****************************************************************************
 * Render: displays previously rendered output
 *****************************************************************************
 * This function send the currently rendered image to Distort image, waits
 * until it is displayed and switch the two rendering buffers, preparing next
 * frame.
 *****************************************************************************/
static picture_t *Filter( filter_t *p_filter, picture_t *p_pic )
{
    picture_t *p_outpic;

    if( !p_pic ) return NULL;

    p_outpic = filter_NewPicture( p_filter );
    if( !p_outpic )
    {
        picture_Release( p_pic );
        return NULL;
    }

    vlc_mutex_lock( &p_filter->p_sys->lock );
    switch( p_filter->p_sys->i_mode )
    {
        case EDGE:
            FilterEdge( p_filter, p_pic, p_outpic );
            break;

        case GRADIENT:
            FilterGradient( p_filter, p_pic, p_outpic );
            break;

        case HOUGH:
            FilterHough( p_filter, p_pic, p_outpic );
            break;

        default:
            break;
    }
    vlc_mutex_unlock( &p_filter->p_sys->lock );

    return CopyInfoAndRelease( p_outpic, p_pic );
}

/*****************************************************************************
 * Gaussian Convolution
 *****************************************************************************
 *    Gaussian convolution ( sigma == 1.4 )
 *
 *    |  2  4  5  4  2  |   |  2  4  4  4  2 |
 *    |  4  9 12  9  4  |   |  4  8 12  8  4 |
 *    |  5 12 15 12  5  | ~ |  4 12 16 12  4 |
 *    |  4  9 12  9  4  |   |  4  8 12  8  4 |
 *    |  2  4  5  4  2  |   |  2  4  4  4  2 |
 *****************************************************************************/
static void GaussianConvolution( picture_t *p_inpic, uint32_t *p_smooth )
{
    const uint8_t *p_inpix = p_inpic->p[Y_PLANE].p_pixels;
    const int i_src_pitch = p_inpic->p[Y_PLANE].i_pitch;
    const int i_src_visible = p_inpic->p[Y_PLANE].i_visible_pitch;
    const int i_num_lines = p_inpic->p[Y_PLANE].i_visible_lines;

    for( int y = 2; y < i_num_lines - 2; y++ )
    {
        for( int x = 2; x < i_src_visible - 2; x++ )
        {
            p_smooth[y*i_src_visible+x] = (uint32_t)(
              /* 2 rows up */
                ( p_inpix[(y-2)*i_src_pitch+x-2] )
              + ((p_inpix[(y-2)*i_src_pitch+x-1]
              +   p_inpix[(y-2)*i_src_pitch+x]
              +   p_inpix[(y-2)*i_src_pitch+x+1])<<1 )
              + ( p_inpix[(y-2)*i_src_pitch+x+2] )
              /* 1 row up */
              + ((p_inpix[(y-1)*i_src_pitch+x-2]
              + ( p_inpix[(y-1)*i_src_pitch+x-1]<<1 )
              + ( p_inpix[(y-1)*i_src_pitch+x]*3 )
              + ( p_inpix[(y-1)*i_src_pitch+x+1]<<1 )
              +   p_inpix[(y-1)*i_src_pitch+x+2]
              /* */
              +   p_inpix[y*i_src_pitch+x-2]
              + ( p_inpix[y*i_src_pitch+x-1]*3 )
              + ( p_inpix[y*i_src_pitch+x]<<2 )
              + ( p_inpix[y*i_src_pitch+x+1]*3 )
              +   p_inpix[y*i_src_pitch+x+2]
              /* 1 row down */
              +   p_inpix[(y+1)*i_src_pitch+x-2]
              + ( p_inpix[(y+1)*i_src_pitch+x-1]<<1 )
              + ( p_inpix[(y+1)*i_src_pitch+x]*3 )
              + ( p_inpix[(y+1)*i_src_pitch+x+1]<<1 )
              +   p_inpix[(y+1)*i_src_pitch+x+2] )<<1 )
              /* 2 rows down */
              + ( p_inpix[(y+2)*i_src_pitch+x-2] )
              + ((p_inpix[(y+2)*i_src_pitch+x-1]
              +   p_inpix[(y+2)*i_src_pitch+x]
              +   p_inpix[(y+2)*i_src_pitch+x+1])<<1 )
              + ( p_inpix[(y+2)*i_src_pitch+x+2] )
              ) >> 6 /* 115 */;
        }
    }
}

/*****************************************************************************
 * FilterGradient: Sobel
 *****************************************************************************/
static void FilterGradient( filter_t *p_filter, picture_t *p_inpic,
                                                picture_t *p_outpic )
{
    const int i_src_pitch = p_inpic->p[Y_PLANE].i_pitch;
    const int i_src_visible = p_inpic->p[Y_PLANE].i_visible_pitch;
    const int i_dst_pitch = p_outpic->p[Y_PLANE].i_pitch;
    const int i_num_lines = p_inpic->p[Y_PLANE].i_visible_lines;

    const uint8_t *p_inpix = p_inpic->p[Y_PLANE].p_pixels;
    uint8_t *p_outpix = p_outpic->p[Y_PLANE].p_pixels;

    uint32_t *p_smooth;
    if( !p_filter->p_sys->p_buf32 )
        p_filter->p_sys->p_buf32 =
            vlc_alloc( i_num_lines * i_src_visible, sizeof(uint32_t));
    p_smooth = p_filter->p_sys->p_buf32;

    if( !p_smooth ) return;

    if( p_filter->p_sys->b_cartoon )
    {
        plane_CopyPixels( &p_outpic->p[U_PLANE], &p_inpic->p[U_PLANE] );
        plane_CopyPixels( &p_outpic->p[V_PLANE], &p_inpic->p[V_PLANE] );
    }
    else
    {
        memset( p_outpic->p[U_PLANE].p_pixels, 0x80,
            p_outpic->p[U_PLANE].i_lines * p_outpic->p[U_PLANE].i_pitch );
        memset( p_outpic->p[V_PLANE].p_pixels, 0x80,
            p_outpic->p[V_PLANE].i_lines * p_outpic->p[V_PLANE].i_pitch );
    }

    GaussianConvolution( p_inpic, p_smooth );

    /* Sobel gradient

     | -1 0 1 |     |  1  2  1 |
     | -2 0 2 | and |  0  0  0 |
     | -1 0 1 |     | -1 -2 -1 | */

#define FOR                                                     \
    for( int y = 1; y < i_num_lines - 1; y++ )                  \
    {                                                           \
        for( int x = 1; x < i_src_visible - 1; x++ )            \
        {                                                       \
            const uint32_t a = \
                  abs(((int)p_smooth[(y - 1) * i_src_visible + x - 1] \
                     - (int)p_smooth[(y + 1) * i_src_visible + x - 1]) \
                   + (((int)p_smooth[(y - 1) * i_src_visible + x] \
                     - (int)p_smooth[(y + 1) * i_src_visible + x]) * 2) \
                    + ((int)p_smooth[(y - 1) * i_src_visible + x + 1] \
                     - (int)p_smooth[(y + 1) * i_src_visible + x + 1])) \
                + abs(((int)p_smooth[(y - 1) * i_src_visible + x - 1] \
                     - (int)p_smooth[(y - 1) * i_src_visible + x + 1]) \
                   + (((int)p_smooth[y       * i_src_visible + x - 1] \
                     - (int)p_smooth[y       * i_src_visible + x + 1]) * 2) \
                    + ((int)p_smooth[(y + 1) * i_src_visible + x - 1] \
                     - (int)p_smooth[(y + 1) * i_src_visible + x + 1]));

    if( p_filter->p_sys->i_gradient_type )
    {
        if( p_filter->p_sys->b_cartoon )
        {
            FOR
            if( a > 60 )
            {
                p_outpix[y*i_dst_pitch+x] = 0x00;
            }
            else
            {
                if( p_smooth[y*i_src_visible+x] > 0xa0 )
                    p_outpix[y*i_dst_pitch+x] =
                        0xff - ((0xff - p_inpix[y*i_src_pitch+x] )>>2);
                else if( p_smooth[y*i_src_visible+x] > 0x70 )
                    p_outpix[y*i_dst_pitch+x] =
                        0xa0 - ((0xa0 - p_inpix[y*i_src_pitch+x] )>>2);
                else if( p_smooth[y*i_src_visible+x] > 0x28 )
                    p_outpix[y*i_dst_pitch+x] =
                        0x70 - ((0x70 - p_inpix[y*i_src_pitch+x] )>>2);
                else
                    p_outpix[y*i_dst_pitch+x] =
                        0x28 - ((0x28 - p_inpix[y*i_src_pitch+x] )>>2);
            }
            }}
        }
        else
        {
            FOR
            p_outpix[y*i_dst_pitch+x] = clip_uint8_vlc( a );
            }}
        }
    }
    else
    {
        FOR
        if( a>>8 )
            p_outpix[y*i_dst_pitch+x] = 0;
        else
            p_outpix[y*i_dst_pitch+x] = 0xff-(uint8_t)a;
        }}
    }
#undef FOR
}

/*****************************************************************************
 * FilterEdge: Canny edge detection algorithm
 *****************************************************************************
 * http://fourier.eng.hmc.edu/e161/lectures/canny/node1.html
 * (well ... my implementation isn't really the canny algorithm ... but some
 * ideas are the same)
 *****************************************************************************/
/* angle : | */
#define THETA_Y 0
/* angle : - */
#define THETA_X 1
/* angle : / */
#define THETA_P 2
/* angle : \ */
#define THETA_M 3
static void FilterEdge( filter_t *p_filter, picture_t *p_inpic,
                                            picture_t *p_outpic )
{
    const int i_src_pitch = p_inpic->p[Y_PLANE].i_pitch;
    const int i_src_visible = p_inpic->p[Y_PLANE].i_visible_pitch;
    const int i_dst_pitch = p_outpic->p[Y_PLANE].i_pitch;
    const int i_num_lines = p_inpic->p[Y_PLANE].i_visible_lines;

    const uint8_t *p_inpix = p_inpic->p[Y_PLANE].p_pixels;
    uint8_t *p_outpix = p_outpic->p[Y_PLANE].p_pixels;

    uint32_t *p_smooth;
    uint32_t *p_grad;
    uint8_t *p_theta;

    if( !p_filter->p_sys->p_buf32 )
        p_filter->p_sys->p_buf32 =
            vlc_alloc( i_num_lines * i_src_visible, sizeof(uint32_t));
    p_smooth = p_filter->p_sys->p_buf32;

    if( !p_filter->p_sys->p_buf32_bis )
        p_filter->p_sys->p_buf32_bis =
            vlc_alloc( i_num_lines * i_src_visible, sizeof(uint32_t));
    p_grad = p_filter->p_sys->p_buf32_bis;

    if( !p_filter->p_sys->p_buf8 )
        p_filter->p_sys->p_buf8 =
            vlc_alloc( i_num_lines * i_src_visible, sizeof(uint8_t));
    p_theta = p_filter->p_sys->p_buf8;

    if( !p_smooth || !p_grad || !p_theta ) return;

    if( p_filter->p_sys->b_cartoon )
    {
        plane_CopyPixels( &p_outpic->p[U_PLANE], &p_inpic->p[U_PLANE] );
        plane_CopyPixels( &p_outpic->p[V_PLANE], &p_inpic->p[V_PLANE] );
    }
    else
    {
        memset( p_outpic->p[Y_PLANE].p_pixels, 0xff,
              p_outpic->p[Y_PLANE].i_lines * p_outpic->p[Y_PLANE].i_pitch );
        memset( p_outpic->p[U_PLANE].p_pixels, 0x80,
            p_outpic->p[U_PLANE].i_lines * p_outpic->p[U_PLANE].i_pitch );
        memset( p_outpic->p[V_PLANE].p_pixels, 0x80,
            p_outpic->p[V_PLANE].i_lines * p_outpic->p[V_PLANE].i_pitch );
    }

    GaussianConvolution( p_inpic, p_smooth );

    /* Sobel gradient

     | -1 0 1 |     |  1  2  1 |
     | -2 0 2 | and |  0  0  0 |
     | -1 0 1 |     | -1 -2 -1 | */

    for( int y = 1; y < i_num_lines - 1; y++ )
    {
        for( int x = 1; x < i_src_visible - 1; x++ )
        {

            const int gradx =
                 ( p_smooth[(y-1)*i_src_visible+x-1]
                   - p_smooth[(y+1)*i_src_visible+x-1] )
               + ( ( p_smooth[(y-1)*i_src_visible+x]
                    - p_smooth[(y+1)*i_src_visible+x] ) <<1 )
               + ( p_smooth[(y-1)*i_src_visible+x+1]
                   - p_smooth[(y+1)*i_src_visible+x+1] );
            const int grady =
                 ( p_smooth[(y-1)*i_src_visible+x-1]
                   - p_smooth[(y-1)*i_src_visible+x+1] )
               + ( ( p_smooth[y*i_src_visible+x-1]
                    - p_smooth[y*i_src_visible+x+1] ) <<1 )
               + ( p_smooth[(y+1)*i_src_visible+x-1]
                   - p_smooth[(y+1)*i_src_visible+x+1] );

            p_grad[y*i_src_visible+x] = (uint32_t)(abs( gradx ) + abs( grady ));

            /* tan( 22.5 ) = 0,414213562 .. * 128 = 53
             * tan( 26,565051177 ) = 0.5
             * tan( 45 + 22.5 ) = 2,414213562 .. * 128 = 309
             * tan( 63,434948823 ) 2 */
            if( (grady<<1) > gradx )
                p_theta[y*i_src_visible+x] = THETA_P;
            else if( (grady<<1) < -gradx )
                p_theta[y*i_src_visible+x] = THETA_M;
            else if( !gradx || abs(grady) > abs(gradx)<<1 )
                p_theta[y*i_src_visible+x] = THETA_Y;
            else
                p_theta[y*i_src_visible+x] = THETA_X;
        }
    }

    /* edge computing */
    for( int y = 1; y < i_num_lines - 1; y++ )
    {
        for( int x = 1; x < i_src_visible - 1; x++ )
        {
            if( p_grad[y*i_src_visible+x] > 40 )
            {
                switch( p_theta[y*i_src_visible+x] )
                {
                    case THETA_Y:
                        if(    p_grad[y*i_src_visible+x] > p_grad[(y-1)*i_src_visible+x]
                            && p_grad[y*i_src_visible+x] > p_grad[(y+1)*i_src_visible+x] )
                        {
                            p_outpix[y*i_dst_pitch+x] = 0;
                            break;
                        } else goto colorize;
                    case THETA_P:
                        if(    p_grad[y*i_src_visible+x] > p_grad[(y-1)*i_src_visible+x-1]
                            && p_grad[y*i_src_visible+x] > p_grad[(y+1)*i_src_visible+x+1] )
                        {
                            p_outpix[y*i_dst_pitch+x] = 0;
                            break;
                        } else goto colorize;
                    case THETA_M:
                        if(    p_grad[y*i_src_visible+x] > p_grad[(y-1)*i_src_visible+x+1]
                            && p_grad[y*i_src_visible+x] > p_grad[(y+1)*i_src_visible+x-1] )
                        {
                            p_outpix[y*i_dst_pitch+x] = 0;
                            break;
                        } else goto colorize;
                    case THETA_X:
                        if(    p_grad[y*i_src_visible+x] > p_grad[y*i_src_visible+x-1]
                            && p_grad[y*i_src_visible+x] > p_grad[y*i_src_visible+x+1] )
                        {
                            p_outpix[y*i_dst_pitch+x] = 0;
                            break;
                        } else goto colorize;
                }
            }
            else
            {
                colorize:
                if( p_filter->p_sys->b_cartoon )
                {
                    if( p_smooth[y*i_src_visible+x] > 0xa0 )
                        p_outpix[y*i_dst_pitch+x] = (uint8_t)
                            0xff - ((0xff - p_inpix[y*i_src_pitch+x] )>>2);
                    else if( p_smooth[y*i_src_visible+x] > 0x70 )
                        p_outpix[y*i_dst_pitch+x] =(uint8_t)
                            0xa0 - ((0xa0 - p_inpix[y*i_src_pitch+x] )>>2);
                    else if( p_smooth[y*i_src_visible+x] > 0x28 )
                        p_outpix[y*i_dst_pitch+x] =(uint8_t)
                            0x70 - ((0x70 - p_inpix[y*i_src_pitch+x] )>>2);
                    else
                        p_outpix[y*i_dst_pitch+x] =(uint8_t)
                            0x28 - ((0x28 - p_inpix[y*i_src_pitch+x] )>>2);
                }
            }
        }
    }
}

/*****************************************************************************
 * FilterHough
 *****************************************************************************/
#define p_pre_hough p_filter->p_sys->p_pre_hough
static void FilterHough( filter_t *p_filter, picture_t *p_inpic,
                                             picture_t *p_outpic )
{
    int i_src_visible = p_inpic->p[Y_PLANE].i_visible_pitch;
    int i_dst_pitch = p_outpic->p[Y_PLANE].i_pitch;
    int i_num_lines = p_inpic->p[Y_PLANE].i_visible_lines;

    uint8_t *p_outpix = p_outpic->p[Y_PLANE].p_pixels;

    int i_diag = sqrt( i_num_lines * i_num_lines +
                        i_src_visible * i_src_visible);
    int i_max, i_phi_max, i_rho, i_rho_max;
    int i_nb_steps = 90;
    double d_step = M_PI / i_nb_steps;
    double d_sin;
    double d_cos;
    uint32_t *p_smooth;

    int *p_hough = vlc_alloc( i_diag * i_nb_steps, sizeof(int) );
    if( ! p_hough ) return;

    p_smooth = vlc_alloc( i_num_lines * i_src_visible, sizeof(uint32_t));
    if( !p_smooth )
    {
        free( p_hough );
        return;
    }

    if( ! p_pre_hough )
    {
        msg_Dbg(p_filter, "Starting precalculation");
        p_pre_hough = vlc_alloc( i_num_lines*i_src_visible*i_nb_steps,sizeof(int));
        if( ! p_pre_hough )
        {
            free( p_smooth );
            free( p_hough );
            return;
        }
        for( int i = 0; i < i_nb_steps; i++)
        {
            d_sin = sin(d_step * i);
            d_cos = cos(d_step * i);
            for( int y = 0; y < i_num_lines; y++ )
                for( int x = 0; x < i_src_visible; x++ )
                {
                    p_pre_hough[(i*i_num_lines+y)*i_src_visible + x] =
                        ceil(x*d_sin + y*d_cos);
                }
        }
        msg_Dbg(p_filter, "Precalculation done");
    }

    memset( p_hough, 0, i_diag * i_nb_steps * sizeof(int) );

    plane_CopyPixels( &p_outpic->p[Y_PLANE], &p_inpic->p[Y_PLANE] );
    plane_CopyPixels( &p_outpic->p[U_PLANE], &p_inpic->p[U_PLANE] );
    plane_CopyPixels( &p_outpic->p[V_PLANE], &p_inpic->p[V_PLANE] );

    GaussianConvolution( p_inpic, p_smooth );

    /* Sobel gradient

     | -1 0 1 |     |  1  2  1 |
     | -2 0 2 | and |  0  0  0 |
     | -1 0 1 |     | -1 -2 -1 | */

    i_max = 0;
    i_rho_max = 0;
    i_phi_max = 0;
    for( int y = 4; y < i_num_lines - 4; y++ )
    {
        for( int x = 4; x < i_src_visible - 4; x++ )
        {
            uint32_t a =
                  abs((((int)p_smooth[(y - 1) * i_src_visible + x]
                      - (int)p_smooth[(y + 1) * i_src_visible + x]) * 2)
                     + ((int)p_smooth[(y - 1) * i_src_visible + x - 1]
                      - (int)p_smooth[(y + 1) * i_src_visible + x - 1])
                     + ((int)p_smooth[(y - 1) * i_src_visible + x + 1]
                      - (int)p_smooth[(y + 1) * i_src_visible + x + 1]))
                + abs((((int)p_smooth[y * i_src_visible + x - 1]
                      - (int)p_smooth[y * i_src_visible + x + 1]) * 2)
                     + ((int)p_smooth[(y - 1) * i_src_visible + x - 1]
                      - (int)p_smooth[(y - 1) * i_src_visible + x + 1])
                     + ((int)p_smooth[(y + 1) * i_src_visible + x - 1]
                      - (int)p_smooth[(y + 1) * i_src_visible + x + 1]));
            if( a>>8 )
            {
                for( int i = 0; i < i_nb_steps; i++ )
                {
                    i_rho = p_pre_hough[(i*i_num_lines+y)*i_src_visible + x];
                    if( p_hough[i_rho + i_diag/2 + i * i_diag]++ > i_max )
                    {
                        i_max = p_hough[i_rho + i_diag/2 + i * i_diag];
                        i_rho_max = i_rho;
                        i_phi_max = i;
                    }
                }
            }
        }
    }

    d_sin = sin(i_phi_max*d_step);
    d_cos = cos(i_phi_max*d_step);
    if( d_cos != 0 )
    {
        for( int x = 0; x < i_src_visible; x++ )
        {
            int y = (i_rho_max - x * d_sin) / d_cos;
            if( y >= 0 && y < i_num_lines )
                p_outpix[y*i_dst_pitch+x] = 255;
        }
    }

    free( p_hough );
    free( p_smooth );
}
#undef p_pre_hough


static int GradientCallback( vlc_object_t *p_this, char const *psz_var,
                             vlc_value_t oldval, vlc_value_t newval,
                             void *p_data )
{
    VLC_UNUSED(oldval);
    filter_sys_t *p_sys = (filter_sys_t *)p_data;

    vlc_mutex_lock( &p_sys->lock );
    if( !strcmp( psz_var, FILTER_PREFIX "mode" ) )
    {
        if( !strcmp( newval.psz_string, "gradient" ) )
        {
            p_sys->i_mode = GRADIENT;
        }
        else if( !strcmp( newval.psz_string, "edge" ) )
        {
            p_sys->i_mode = EDGE;
        }
        else if( !strcmp( newval.psz_string, "hough" ) )
        {
            p_sys->i_mode = HOUGH;
        }
        else
        {
            msg_Err( p_this, "no valid gradient mode provided (%s)", newval.psz_string );
            p_sys->i_mode = GRADIENT;
        }
    }
    else if( !strcmp( psz_var, FILTER_PREFIX "type" ) )
    {
        p_sys->i_gradient_type = newval.i_int;
    }
    else if( !strcmp( psz_var, FILTER_PREFIX "cartoon" ) )
    {
        p_sys->b_cartoon = newval.b_bool;
    }
    vlc_mutex_unlock( &p_sys->lock );

    return VLC_SUCCESS;
}
