/*
  * Copyright (c) 2012 Clément Bœsch
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg 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.
  *
  * FFmpeg 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 FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 /**
  * @file
  * Edge detection filter
  *

  * @see https://en.wikipedia.org/wiki/Canny_edge_detector

  */
 
 #include "libavutil/opt.h"
 #include "avfilter.h"
 #include "formats.h"
 #include "internal.h"
 #include "video.h"
 
 typedef struct {
     const AVClass *class;
     uint8_t  *tmpbuf;
     uint16_t *gradients;
     char     *directions;
     double   low, high;
     uint8_t  low_u8, high_u8;
 } EdgeDetectContext;
 
 #define OFFSET(x) offsetof(EdgeDetectContext, x)

 #define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM

 static const AVOption edgedetect_options[] = {

     { "high", "set high threshold", OFFSET(high), AV_OPT_TYPE_DOUBLE, {.dbl=50/255.}, 0, 1, FLAGS },
     { "low",  "set low threshold",  OFFSET(low),  AV_OPT_TYPE_DOUBLE, {.dbl=20/255.}, 0, 1, FLAGS },

     { NULL },
 };
 
 AVFILTER_DEFINE_CLASS(edgedetect);
 
 static av_cold int init(AVFilterContext *ctx, const char *args)
 {
     int ret;
     EdgeDetectContext *edgedetect = ctx->priv;
 
     edgedetect->class = &edgedetect_class;
     av_opt_set_defaults(edgedetect);
 
     if ((ret = av_set_options_string(edgedetect, args, "=", ":")) < 0)
         return ret;
 

     edgedetect->low_u8  = edgedetect->low  * 255. + .5;
     edgedetect->high_u8 = edgedetect->high * 255. + .5;

     return 0;
 }
 
 static int query_formats(AVFilterContext *ctx)
 {

     static const enum AVPixelFormat pix_fmts[] = {AV_PIX_FMT_GRAY8, AV_PIX_FMT_NONE};

     ff_set_common_formats(ctx, ff_make_format_list(pix_fmts));
     return 0;
 }
 
 static int config_props(AVFilterLink *inlink)
 {
     AVFilterContext *ctx = inlink->dst;
     EdgeDetectContext *edgedetect = ctx->priv;
 
     edgedetect->tmpbuf     = av_malloc(inlink->w * inlink->h);
     edgedetect->gradients  = av_calloc(inlink->w * inlink->h, sizeof(*edgedetect->gradients));
     edgedetect->directions = av_malloc(inlink->w * inlink->h);
     if (!edgedetect->tmpbuf || !edgedetect->gradients || !edgedetect->directions)
         return AVERROR(ENOMEM);
     return 0;
 }
 
 static void gaussian_blur(AVFilterContext *ctx, int w, int h,
                                 uint8_t *dst, int dst_linesize,
                           const uint8_t *src, int src_linesize)
 {
     int i, j;
 
     memcpy(dst, src, w); dst += dst_linesize; src += src_linesize;
     memcpy(dst, src, w); dst += dst_linesize; src += src_linesize;
     for (j = 2; j < h - 2; j++) {
         dst[0] = src[0];
         dst[1] = src[1];
         for (i = 2; i < w - 2; i++) {
             /* Gaussian mask of size 5x5 with sigma = 1.4 */
             dst[i] = ((src[-2*src_linesize + i-2] + src[2*src_linesize + i-2]) * 2
                     + (src[-2*src_linesize + i-1] + src[2*src_linesize + i-1]) * 4
                     + (src[-2*src_linesize + i  ] + src[2*src_linesize + i  ]) * 5
                     + (src[-2*src_linesize + i+1] + src[2*src_linesize + i+1]) * 4
                     + (src[-2*src_linesize + i+2] + src[2*src_linesize + i+2]) * 2
 
                     + (src[  -src_linesize + i-2] + src[  src_linesize + i-2]) *  4
                     + (src[  -src_linesize + i-1] + src[  src_linesize + i-1]) *  9
                     + (src[  -src_linesize + i  ] + src[  src_linesize + i  ]) * 12
                     + (src[  -src_linesize + i+1] + src[  src_linesize + i+1]) *  9
                     + (src[  -src_linesize + i+2] + src[  src_linesize + i+2]) *  4
 
                     + src[i-2] *  5
                     + src[i-1] * 12
                     + src[i  ] * 15
                     + src[i+1] * 12
                     + src[i+2] *  5) / 159;
         }
         dst[i    ] = src[i    ];
         dst[i + 1] = src[i + 1];
 
         dst += dst_linesize;
         src += src_linesize;
     }
     memcpy(dst, src, w); dst += dst_linesize; src += src_linesize;
     memcpy(dst, src, w);
 }
 
 enum {
     DIRECTION_45UP,
     DIRECTION_45DOWN,
     DIRECTION_HORIZONTAL,
     DIRECTION_VERTICAL,
 };
 
 static int get_rounded_direction(int gx, int gy)
 {
     /* reference angles:
      *   tan( pi/8) = sqrt(2)-1
      *   tan(3pi/8) = sqrt(2)+1
      * Gy/Gx is the tangent of the angle (theta), so Gy/Gx is compared against
      * <ref-angle>, or more simply Gy against <ref-angle>*Gx
      *

      * Gx and Gy bounds = [-1020;1020], using 16-bit arithmetic:

      *   round((sqrt(2)-1) * (1<<16)) =  27146
      *   round((sqrt(2)+1) * (1<<16)) = 158218
      */
     if (gx) {
         int tanpi8gx, tan3pi8gx;
 
         if (gx < 0)
             gx = -gx, gy = -gy;
         gy <<= 16;
         tanpi8gx  =  27146 * gx;
         tan3pi8gx = 158218 * gx;
         if (gy > -tan3pi8gx && gy < -tanpi8gx)  return DIRECTION_45UP;
         if (gy > -tanpi8gx  && gy <  tanpi8gx)  return DIRECTION_HORIZONTAL;
         if (gy >  tanpi8gx  && gy <  tan3pi8gx) return DIRECTION_45DOWN;
     }
     return DIRECTION_VERTICAL;
 }
 
 static void sobel(AVFilterContext *ctx, int w, int h,
                         uint16_t *dst, int dst_linesize,
                   const uint8_t  *src, int src_linesize)
 {
     int i, j;
     EdgeDetectContext *edgedetect = ctx->priv;
 
     for (j = 1; j < h - 1; j++) {
         dst += dst_linesize;
         src += src_linesize;
         for (i = 1; i < w - 1; i++) {
             const int gx =
                 -1*src[-src_linesize + i-1] + 1*src[-src_linesize + i+1]
                 -2*src[                i-1] + 2*src[                i+1]
                 -1*src[ src_linesize + i-1] + 1*src[ src_linesize + i+1];
             const int gy =
                 -1*src[-src_linesize + i-1] + 1*src[ src_linesize + i-1]
                 -2*src[-src_linesize + i  ] + 2*src[ src_linesize + i  ]
                 -1*src[-src_linesize + i+1] + 1*src[ src_linesize + i+1];
 
             dst[i] = FFABS(gx) + FFABS(gy);
             edgedetect->directions[j*w + i] = get_rounded_direction(gx, gy);
         }
     }
 }
 
 static void non_maximum_suppression(AVFilterContext *ctx, int w, int h,
                                           uint8_t  *dst, int dst_linesize,
                                     const uint16_t *src, int src_linesize)
 {
     int i, j;
     EdgeDetectContext *edgedetect = ctx->priv;
 
 #define COPY_MAXIMA(ay, ax, by, bx) do {                \
     if (src[i] > src[(ay)*src_linesize + i+(ax)] &&     \
         src[i] > src[(by)*src_linesize + i+(bx)])       \
         dst[i] = av_clip_uint8(src[i]);                 \
 } while (0)
 
     for (j = 1; j < h - 1; j++) {
         dst += dst_linesize;
         src += src_linesize;
         for (i = 1; i < w - 1; i++) {
             switch (edgedetect->directions[j*w + i]) {
             case DIRECTION_45UP:        COPY_MAXIMA( 1, -1, -1,  1); break;
             case DIRECTION_45DOWN:      COPY_MAXIMA(-1, -1,  1,  1); break;
             case DIRECTION_HORIZONTAL:  COPY_MAXIMA( 0, -1,  0,  1); break;
             case DIRECTION_VERTICAL:    COPY_MAXIMA(-1,  0,  1,  0); break;
             }
         }
     }
 }
 
 static void double_threshold(AVFilterContext *ctx, int w, int h,
                                    uint8_t *dst, int dst_linesize,
                              const uint8_t *src, int src_linesize)
 {
     int i, j;
     EdgeDetectContext *edgedetect = ctx->priv;
     const int low  = edgedetect->low_u8;
     const int high = edgedetect->high_u8;
 
     for (j = 0; j < h; j++) {
         for (i = 0; i < w; i++) {
             if (src[i] > high) {
                 dst[i] = src[i];
                 continue;
             }
 
             if ((!i || i == w - 1 || !j || j == h - 1) &&
                 src[i] > low &&
                 (src[-src_linesize + i-1] > high ||
                  src[-src_linesize + i  ] > high ||
                  src[-src_linesize + i+1] > high ||
                  src[                i-1] > high ||
                  src[                i+1] > high ||
                  src[ src_linesize + i-1] > high ||
                  src[ src_linesize + i  ] > high ||
                  src[ src_linesize + i+1] > high))
                 dst[i] = src[i];
             else
                 dst[i] = 0;
         }
         dst += dst_linesize;
         src += src_linesize;
     }
 }
 

 static int filter_frame(AVFilterLink *inlink, AVFilterBufferRef *in)

 {
     AVFilterContext *ctx = inlink->dst;
     EdgeDetectContext *edgedetect = ctx->priv;
     AVFilterLink *outlink = inlink->dst->outputs[0];
     uint8_t  *tmpbuf    = edgedetect->tmpbuf;
     uint16_t *gradients = edgedetect->gradients;

     AVFilterBufferRef *out;
 
     out = ff_get_video_buffer(outlink, AV_PERM_WRITE, outlink->w, outlink->h);
     if (!out) {
         avfilter_unref_bufferp(&in);
         return AVERROR(ENOMEM);
     }
     avfilter_copy_buffer_ref_props(out, in);

 
     /* gaussian filter to reduce noise  */
     gaussian_blur(ctx, inlink->w, inlink->h,

                   tmpbuf,      inlink->w,
                   in->data[0], in->linesize[0]);

 
     /* compute the 16-bits gradients and directions for the next step */
     sobel(ctx, inlink->w, inlink->h,
           gradients, inlink->w,
           tmpbuf,    inlink->w);
 
     /* non_maximum_suppression() will actually keep & clip what's necessary and
      * ignore the rest, so we need a clean output buffer */
     memset(tmpbuf, 0, inlink->w * inlink->h);
     non_maximum_suppression(ctx, inlink->w, inlink->h,
                             tmpbuf,    inlink->w,
                             gradients, inlink->w);
 
     /* keep high values, or low values surrounded by high values */
     double_threshold(ctx, inlink->w, inlink->h,

                      out->data[0], out->linesize[0],
                      tmpbuf,       inlink->w);

     avfilter_unref_bufferp(&in);
     return ff_filter_frame(outlink, out);

 }
 
 static av_cold void uninit(AVFilterContext *ctx)
 {
     EdgeDetectContext *edgedetect = ctx->priv;
     av_freep(&edgedetect->tmpbuf);
     av_freep(&edgedetect->gradients);
     av_freep(&edgedetect->directions);
 }
 

 static const AVFilterPad edgedetect_inputs[] = {
     {
         .name         = "default",
         .type         = AVMEDIA_TYPE_VIDEO,
         .config_props = config_props,
         .filter_frame = filter_frame,
         .min_perms    = AV_PERM_READ,
      },
      { NULL }
 };
 
 static const AVFilterPad edgedetect_outputs[] = {
      {
          .name = "default",
          .type = AVMEDIA_TYPE_VIDEO,
      },
      { NULL }
 };
 

 AVFilter avfilter_vf_edgedetect = {
     .name          = "edgedetect",
     .description   = NULL_IF_CONFIG_SMALL("Detect and draw edge."),
     .priv_size     = sizeof(EdgeDetectContext),
     .init          = init,
     .uninit        = uninit,
     .query_formats = query_formats,

     .inputs        = edgedetect_inputs,
     .outputs       = edgedetect_outputs,

     .priv_class    = &edgedetect_class,

 };