text: /*
   * Copyright (c) 2002 Michael Niedermayer <michaelni@gmx.at>
   * Copyright (c) 2013 Paul B Mahol
   *
   * This file is part of FFmpeg.
   *
   * FFmpeg is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public
   * License as published by the Free Software Foundation; either
   * version 2 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 General Public License for more details.
   *
   * You should have received a copy of the GNU 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
   */
  
  #include "libavutil/eval.h"
  #include "libavutil/imgutils.h"
  #include "libavutil/pixdesc.h"
  #include "libavutil/opt.h"
  #include "avfilter.h"
  #include "formats.h"
  #include "internal.h"
  #include "video.h"
  
  #define SUB_PIXEL_BITS  8
  #define SUB_PIXELS      (1 << SUB_PIXEL_BITS)
  #define COEFF_BITS      11
  
  #define LINEAR 0
  #define CUBIC  1
  
  typedef struct PerspectiveContext {
      const AVClass *class;
      char *expr_str[4][2];
      double ref[4][2];
      int32_t (*pv)[2];
      int32_t coeff[SUB_PIXELS][4];
      int interpolation;
      int linesize[4];
      int height[4];
      int hsub, vsub;
      int nb_planes;
  
      void (*perspective)(struct PerspectiveContext *s,
                          uint8_t *dst, int dst_linesize,
                          uint8_t *src, int src_linesize,
                          int w, int h, int hsub, int vsub);
  } PerspectiveContext;
  
  #define OFFSET(x) offsetof(PerspectiveContext, x)
  #define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM
  
  static const AVOption perspective_options[] = {
      { "x0", "set top left x coordinate",     OFFSET(expr_str[0][0]), AV_OPT_TYPE_STRING, {.str="0"}, 0, 0, FLAGS },
      { "y0", "set top left y coordinate",     OFFSET(expr_str[0][1]), AV_OPT_TYPE_STRING, {.str="0"}, 0, 0, FLAGS },
      { "x1", "set top right x coordinate",    OFFSET(expr_str[1][0]), AV_OPT_TYPE_STRING, {.str="W"}, 0, 0, FLAGS },
      { "y1", "set top right y coordinate",    OFFSET(expr_str[1][1]), AV_OPT_TYPE_STRING, {.str="0"}, 0, 0, FLAGS },
      { "x2", "set bottom left x coordinate",  OFFSET(expr_str[2][0]), AV_OPT_TYPE_STRING, {.str="0"}, 0, 0, FLAGS },
      { "y2", "set bottom left y coordinate",  OFFSET(expr_str[2][1]), AV_OPT_TYPE_STRING, {.str="H"}, 0, 0, FLAGS },
      { "x3", "set bottom right x coordinate", OFFSET(expr_str[3][0]), AV_OPT_TYPE_STRING, {.str="W"}, 0, 0, FLAGS },
      { "y3", "set bottom right y coordinate", OFFSET(expr_str[3][1]), AV_OPT_TYPE_STRING, {.str="H"}, 0, 0, FLAGS },
      { "interpolation", "set interpolation", OFFSET(interpolation), AV_OPT_TYPE_INT, {.i64=LINEAR}, 0, 1, FLAGS, "interpolation" },
      {      "linear", "", 0, AV_OPT_TYPE_CONST, {.i64=LINEAR}, 0, 0, FLAGS, "interpolation" },
      {       "cubic", "", 0, AV_OPT_TYPE_CONST, {.i64=CUBIC},  0, 0, FLAGS, "interpolation" },
      { NULL }
  };
  
  AVFILTER_DEFINE_CLASS(perspective);
  
  static int query_formats(AVFilterContext *ctx)
  {
      static const enum AVPixelFormat pix_fmts[] = {
          AV_PIX_FMT_YUVA444P, AV_PIX_FMT_YUVA422P, AV_PIX_FMT_YUVA420P,
          AV_PIX_FMT_YUVJ444P, AV_PIX_FMT_YUVJ440P, AV_PIX_FMT_YUVJ422P,AV_PIX_FMT_YUVJ420P, AV_PIX_FMT_YUVJ411P,
          AV_PIX_FMT_YUV444P, AV_PIX_FMT_YUV440P, AV_PIX_FMT_YUV422P, AV_PIX_FMT_YUV420P, AV_PIX_FMT_YUV411P, AV_PIX_FMT_YUV410P,
          AV_PIX_FMT_GBRP, AV_PIX_FMT_GBRAP, AV_PIX_FMT_GRAY8, AV_PIX_FMT_NONE
      };
  
      ff_set_common_formats(ctx, ff_make_format_list(pix_fmts));
      return 0;
  }
  
  static inline double get_coeff(double d)
  {
      double coeff, A = -0.60;
  
      d = fabs(d);
  
      if (d < 1.0)
          coeff = (1.0 - (A + 3.0) * d * d + (A + 2.0) * d * d * d);
      else if (d < 2.0)
          coeff = (-4.0 * A + 8.0 * A * d - 5.0 * A * d * d + A * d * d * d);
      else
          coeff = 0.0;
  
      return coeff;
  }
  
  static const char *const var_names[] = {   "W",   "H", NULL };
  enum                                   { VAR_W, VAR_H, VAR_VARS_NB };
  
  static int config_input(AVFilterLink *inlink)
  {
      double x0, x1, x2, x3, x4, x5, x6, x7, q;
      AVFilterContext *ctx = inlink->dst;
      PerspectiveContext *s = ctx->priv;
      double (*ref)[2] = s->ref;
      const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(inlink->format);
      double values[VAR_VARS_NB] = { [VAR_W] = inlink->w, [VAR_H] = inlink->h };
      int h = inlink->h;
      int w = inlink->w;
      int x, y, i, j, ret;
  
      for (i = 0; i < 4; i++) {
          for (j = 0; j < 2; j++) {
              if (!s->expr_str[i][j])
                  return AVERROR(EINVAL);
              ret = av_expr_parse_and_eval(&s->ref[i][j], s->expr_str[i][j],
                                           var_names, &values[0],
                                           NULL, NULL, NULL, NULL,
                                           0, 0, ctx);
              if (ret < 0)
                  return ret;
          }
      }
  
      s->hsub = desc->log2_chroma_w;
      s->vsub = desc->log2_chroma_h;
      s->nb_planes = av_pix_fmt_count_planes(inlink->format);
      if ((ret = av_image_fill_linesizes(s->linesize, inlink->format, inlink->w)) < 0)
          return ret;
  
      s->height[1] = s->height[2] = FF_CEIL_RSHIFT(inlink->h, desc->log2_chroma_h);
      s->height[0] = s->height[3] = inlink->h;
  
      s->pv = av_realloc_f(s->pv, w * h, 2 * sizeof(*s->pv));
      if (!s->pv)
          return AVERROR(ENOMEM);
  
      x6 = ((ref[0][0] - ref[1][0] - ref[2][0] + ref[3][0]) *
            (ref[2][1] - ref[3][1]) -
           ( ref[0][1] - ref[1][1] - ref[2][1] + ref[3][1]) *
            (ref[2][0] - ref[3][0])) * h;
      x7 = ((ref[0][1] - ref[1][1] - ref[2][1] + ref[3][1]) *
            (ref[1][0] - ref[3][0]) -
           ( ref[0][0] - ref[1][0] - ref[2][0] + ref[3][0]) *
            (ref[1][1] - ref[3][1])) * w;
      q =  ( ref[1][0] - ref[3][0]) * (ref[2][1] - ref[3][1]) -
           ( ref[2][0] - ref[3][0]) * (ref[1][1] - ref[3][1]);
  
      x0 = q * (ref[1][0] - ref[0][0]) * h + x6 * ref[1][0];
      x1 = q * (ref[2][0] - ref[0][0]) * w + x7 * ref[2][0];
      x2 = q *  ref[0][0] * w * h;
      x3 = q * (ref[1][1] - ref[0][1]) * h + x6 * ref[1][1];
      x4 = q * (ref[2][1] - ref[0][1]) * w + x7 * ref[2][1];
      x5 = q *  ref[0][1] * w * h;
  
      for (y = 0; y < h; y++){
          for (x = 0; x < w; x++){
              int u, v;
  
              u = (int)floor(SUB_PIXELS * (x0 * x + x1 * y + x2) /
                                          (x6 * x + x7 * y + q * w * h) + 0.5);
              v = (int)floor(SUB_PIXELS * (x3 * x + x4 * y + x5) /
                                          (x6 * x + x7 * y + q * w * h) + 0.5);
  
              s->pv[x + y * w][0] = u;
              s->pv[x + y * w][1] = v;
          }
      }
  
      for (i = 0; i < SUB_PIXELS; i++){
          double d = i / (double)SUB_PIXELS;
          double temp[4];
          double sum = 0;
  
          for (j = 0; j < 4; j++)
              temp[j] = get_coeff(j - d - 1);
  
          for (j = 0; j < 4; j++)
              sum += temp[j];
  
          for (j = 0; j < 4; j++)
              s->coeff[i][j] = (int)floor((1 << COEFF_BITS) * temp[j] / sum + 0.5);
      }
  
      return 0;
  }
  
  static void resample_cubic(PerspectiveContext *s,
                             uint8_t *dst, int dst_linesize,
                             uint8_t *src, int src_linesize,
                             int w, int h, int hsub, int vsub)
  {
      const int linesize = s->linesize[0];
      int x, y;
  
      for (y = 0; y < h; y++) {
          int sy = y << vsub;
          for (x = 0; x < w; x++) {
              int u, v, subU, subV, sum, sx;
  
              sx   = x << hsub;
              u    = s->pv[sx + sy * linesize][0] >> hsub;
              v    = s->pv[sx + sy * linesize][1] >> vsub;
              subU = u & (SUB_PIXELS - 1);
              subV = v & (SUB_PIXELS - 1);
              u  >>= SUB_PIXEL_BITS;
              v  >>= SUB_PIXEL_BITS;
  
              if (u > 0 && v > 0 && u < w - 2 && v < h - 2){
                  const int index = u + v*src_linesize;
                  const int a = s->coeff[subU][0];
                  const int b = s->coeff[subU][1];
                  const int c = s->coeff[subU][2];
                  const int d = s->coeff[subU][3];
  
                  sum = s->coeff[subV][0] * (a * src[index - 1 -     src_linesize] + b * src[index - 0 -     src_linesize]  +
                                        c *      src[index + 1 -     src_linesize] + d * src[index + 2 -     src_linesize]) +
                        s->coeff[subV][1] * (a * src[index - 1                   ] + b * src[index - 0                   ]  +
                                        c *      src[index + 1                   ] + d * src[index + 2                   ]) +
                        s->coeff[subV][2] * (a * src[index - 1 +     src_linesize] + b * src[index - 0 +     src_linesize]  +
                                        c *      src[index + 1 +     src_linesize] + d * src[index + 2 +     src_linesize]) +
                        s->coeff[subV][3] * (a * src[index - 1 + 2 * src_linesize] + b * src[index - 0 + 2 * src_linesize]  +
                                        c *      src[index + 1 + 2 * src_linesize] + d * src[index + 2 + 2 * src_linesize]);
              } else {
                  int dx, dy;
  
                  sum = 0;
  
                  for (dy = 0; dy < 4; dy++) {
                      int iy = v + dy - 1;
  
                      if (iy < 0)
                          iy = 0;
                      else if (iy >= h)
                          iy = h-1;
                      for (dx = 0; dx < 4; dx++) {
                          int ix = u + dx - 1;
  
                          if (ix < 0)
                              ix = 0;
                          else if (ix >= w)
                              ix = w - 1;
  
                          sum += s->coeff[subU][dx] * s->coeff[subV][dy] * src[ ix + iy * src_linesize];
                      }
                  }
              }
  
              sum = (sum + (1<<(COEFF_BITS * 2 - 1))) >> (COEFF_BITS * 2);
              sum = av_clip(sum, 0, 255);
              dst[x + y * dst_linesize] = sum;
          }
      }
  }
  
  static void resample_linear(PerspectiveContext *s,
                              uint8_t *dst, int dst_linesize,
                              uint8_t *src, int src_linesize,
                              int w, int h, int hsub, int vsub)
  {
      const int linesize = s->linesize[0];
      int x, y;
  
      for (y = 0; y < h; y++){
          int sy = y << vsub;
          for (x = 0; x < w; x++){
              int u, v, subU, subV, sum, sx, index, subUI, subVI;
  
              sx   = x << hsub;
              u    = s->pv[sx + sy * linesize][0] >> hsub;
              v    = s->pv[sx + sy * linesize][1] >> vsub;
              subU = u & (SUB_PIXELS - 1);
              subV = v & (SUB_PIXELS - 1);
              u  >>= SUB_PIXEL_BITS;
              v  >>= SUB_PIXEL_BITS;
  
              index = u + v * src_linesize;
              subUI = SUB_PIXELS - subU;
              subVI = SUB_PIXELS - subV;
  
              if ((unsigned)u < (unsigned)(w - 1)){
                  if((unsigned)v < (unsigned)(h - 1)){
                      sum = subVI * (subUI * src[index] + subU * src[index + 1]) +
                            subV  * (subUI * src[index + src_linesize] + subU * src[index + src_linesize + 1]);
                      sum = (sum + (1 << (SUB_PIXEL_BITS * 2 - 1)))>> (SUB_PIXEL_BITS * 2);
                  } else {
                      if (v < 0)
                          v = 0;
                      else
                          v = h - 1;
                      index = u + v * src_linesize;
                      sum   = subUI * src[index] + subU * src[index + 1];
                      sum   = (sum + (1 << (SUB_PIXEL_BITS - 1))) >> SUB_PIXEL_BITS;
                  }
              } else {
                  if ((unsigned)v < (unsigned)(h - 1)){
                      if (u < 0)
                          u = 0;
                      else
                          u = w - 1;
                      index = u + v * src_linesize;
                      sum   = subVI * src[index] + subV * src[index + src_linesize];
                      sum   = (sum + (1 << (SUB_PIXEL_BITS - 1))) >> SUB_PIXEL_BITS;
                  } else {
                      if (u < 0)
                          u = 0;
                      else
                          u = w - 1;
                      if (v < 0)
                          v = 0;
                      else
                          v = h - 1;
                      index = u + v * src_linesize;
                      sum   = src[index];
                  }
              }
  
              sum = av_clip(sum, 0, 255);
              dst[x + y * dst_linesize] = sum;
          }
      }
  }
  
  static av_cold int init(AVFilterContext *ctx)
  {
      PerspectiveContext *s = ctx->priv;
  
      switch (s->interpolation) {
      case LINEAR: s->perspective = resample_linear; break;
      case CUBIC:  s->perspective = resample_cubic;  break;
      }
  
      return 0;
  }
  
  static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
  {
      AVFilterContext *ctx = inlink->dst;
      AVFilterLink *outlink = ctx->outputs[0];
      PerspectiveContext *s = ctx->priv;
      AVFrame *out;
      int plane;
  
      out = ff_get_video_buffer(outlink, outlink->w, outlink->h);
      if (!out) {
          av_frame_free(&frame);
          return AVERROR(ENOMEM);
      }
      av_frame_copy_props(out, frame);
  
      for (plane = 0; plane < s->nb_planes; plane++) {
          int hsub = plane == 1 || plane == 2 ? s->hsub : 0;
          int vsub = plane == 1 || plane == 2 ? s->vsub : 0;
          s->perspective(s, out->data[plane], out->linesize[plane],
                         frame->data[plane], frame->linesize[plane],
                         s->linesize[plane], s->height[plane], hsub, vsub);
      }
  
      av_frame_free(&frame);
      return ff_filter_frame(outlink, out);
  }
  
  static av_cold void uninit(AVFilterContext *ctx)
  {
      PerspectiveContext *s = ctx->priv;
  
      av_freep(&s->pv);
  }
  
  static const AVFilterPad perspective_inputs[] = {
      {
          .name             = "default",
          .type             = AVMEDIA_TYPE_VIDEO,
          .filter_frame     = filter_frame,
          .config_props     = config_input,
      },
      { NULL }
  };
  
  static const AVFilterPad perspective_outputs[] = {
      {
          .name          = "default",
          .type          = AVMEDIA_TYPE_VIDEO,
      },
      { NULL }
  };
  
  AVFilter avfilter_vf_perspective = {
      .name          = "perspective",
      .description   = NULL_IF_CONFIG_SMALL("Correct the perspective of video."),
      .priv_size     = sizeof(PerspectiveContext),
      .init          = init,
      .uninit        = uninit,
      .query_formats = query_formats,
      .inputs        = perspective_inputs,
      .outputs       = perspective_outputs,
      .priv_class    = &perspective_class,
      .flags         = AVFILTER_FLAG_SUPPORT_TIMELINE_GENERIC,
  };
  