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/*

 * Copyright (c) 2015 Stupeflix

 *

 * 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

 * Generate one palette for a whole video stream.

 */

#include "libavutil/avassert.h"

#include "libavutil/internal.h"

#include "libavutil/opt.h"

#include "libavutil/qsort.h"

#include "avfilter.h"

#include "internal.h"

/* Reference a color and how much it's used */

struct color_ref {

    uint32_t color;

    uint64_t count;

};

/* Store a range of colors */

struct range_box {

    uint32_t color;     // average color

    int64_t variance;   // overall variance of the box (how much the colors are spread)

    int start;          // index in PaletteGenContext->refs

    int len;            // number of referenced colors

    int sorted_by;      // whether range of colors is sorted by red (0), green (1) or blue (2)

};

struct hist_node {

    struct color_ref *entries;

    int nb_entries;

};

enum {

    STATS_MODE_ALL_FRAMES,

    STATS_MODE_DIFF_FRAMES,

    NB_STATS_MODE

};

#define NBITS 5

#define HIST_SIZE (1<<(3*NBITS))

typedef struct {

    const AVClass *class;

    int max_colors;

    int reserve_transparent;

    int stats_mode;

    AVFrame *prev_frame;                    // previous frame used for the diff stats_mode

    struct hist_node histogram[HIST_SIZE];  // histogram/hashtable of the colors

    struct color_ref **refs;                // references of all the colors used in the stream

    int nb_refs;                            // number of color references (or number of different colors)

    struct range_box boxes[256];            // define the segmentation of the colorspace (the final palette)

    int nb_boxes;                           // number of boxes (increase will segmenting them)

    int palette_pushed;                     // if the palette frame is pushed into the outlink or not

} PaletteGenContext;

#define OFFSET(x) offsetof(PaletteGenContext, x)

#define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM

static const AVOption palettegen_options[] = {

    { "max_colors", "set the maximum number of colors to use in the palette", OFFSET(max_colors), AV_OPT_TYPE_INT, {.i64=256}, 4, 256, FLAGS },

    { "reserve_transparent", "reserve a palette entry for transparency", OFFSET(reserve_transparent), AV_OPT_TYPE_INT, {.i64=1}, 0, 1, FLAGS },

    { "stats_mode", "set statistics mode", OFFSET(stats_mode), AV_OPT_TYPE_INT, {.i64=STATS_MODE_ALL_FRAMES}, 0, NB_STATS_MODE, FLAGS, "mode" },

        { "full", "compute full frame histograms", 0, AV_OPT_TYPE_CONST, {.i64=STATS_MODE_ALL_FRAMES}, INT_MIN, INT_MAX, FLAGS, "mode" },

        { "diff", "compute histograms only for the part that differs from previous frame", 0, AV_OPT_TYPE_CONST, {.i64=STATS_MODE_DIFF_FRAMES}, INT_MIN, INT_MAX, FLAGS, "mode" },

    { NULL }

};

AVFILTER_DEFINE_CLASS(palettegen);

static int query_formats(AVFilterContext *ctx)

{

    static const enum AVPixelFormat in_fmts[]  = {AV_PIX_FMT_RGB32, AV_PIX_FMT_NONE};

    static const enum AVPixelFormat out_fmts[] = {AV_PIX_FMT_RGB32, AV_PIX_FMT_NONE};

    AVFilterFormats *in  = ff_make_format_list(in_fmts);

    AVFilterFormats *out = ff_make_format_list(out_fmts);

    if (!in || !out) {

        av_freep(&in);

        av_freep(&out);

        return AVERROR(ENOMEM);

    }

    ff_formats_ref(in,  &ctx->inputs[0]->out_formats);

    ff_formats_ref(out, &ctx->outputs[0]->in_formats);

    return 0;

}

typedef int (*cmp_func)(const void *, const void *);

#define DECLARE_CMP_FUNC(name, pos)                     \

static int cmp_##name(const void *pa, const void *pb)   \

{                                                       \

    const struct color_ref * const *a = pa;             \

    const struct color_ref * const *b = pb;             \

    return   ((*a)->color >> (8 * (2 - (pos))) & 0xff)  \

           - ((*b)->color >> (8 * (2 - (pos))) & 0xff); \

}

DECLARE_CMP_FUNC(r, 0)

DECLARE_CMP_FUNC(g, 1)

DECLARE_CMP_FUNC(b, 2)

static const cmp_func cmp_funcs[] = {cmp_r, cmp_g, cmp_b};

/**

 * Simple color comparison for sorting the final palette

 */

static int cmp_color(const void *a, const void *b)

{

    const struct range_box *box1 = a;

    const struct range_box *box2 = b;

    return box1->color - box2->color;

}

static av_always_inline int diff(const uint32_t a, const uint32_t b)

{

    const uint8_t c1[] = {a >> 16 & 0xff, a >> 8 & 0xff, a & 0xff};

    const uint8_t c2[] = {b >> 16 & 0xff, b >> 8 & 0xff, b & 0xff};

    const int dr = c1[0] - c2[0];

    const int dg = c1[1] - c2[1];

    const int db = c1[2] - c2[2];

    return dr*dr + dg*dg + db*db;

}

/**

 * Find the next box to split: pick the one with the highest variance

 */

static int get_next_box_id_to_split(PaletteGenContext *s)

{

    int box_id, i, best_box_id = -1;

    int64_t max_variance = -1;

    if (s->nb_boxes == s->max_colors - s->reserve_transparent)

        return -1;

    for (box_id = 0; box_id < s->nb_boxes; box_id++) {

        struct range_box *box = &s->boxes[box_id];

        if (s->boxes[box_id].len >= 2) {

            if (box->variance == -1) {

                int64_t variance = 0;

                for (i = 0; i < box->len; i++) {

                    const struct color_ref *ref = s->refs[box->start + i];

                    variance += diff(ref->color, box->color) * ref->count;

                }

                box->variance = variance;

            }

            if (box->variance > max_variance) {

                best_box_id = box_id;

                max_variance = box->variance;

            }

        } else {

            box->variance = -1;

        }

    }

    return best_box_id;

}

/**

 * Get the 32-bit average color for the range of RGB colors enclosed in the

 * specified box. Takes into account the weight of each color.

 */

static uint32_t get_avg_color(struct color_ref * const *refs,

                              const struct range_box *box)

{

    int i;

    const int n = box->len;

    uint64_t r = 0, g = 0, b = 0, div = 0;

    for (i = 0; i < n; i++) {

        const struct color_ref *ref = refs[box->start + i];

        r += (ref->color >> 16 & 0xff) * ref->count;

        g += (ref->color >>  8 & 0xff) * ref->count;

        b += (ref->color       & 0xff) * ref->count;

        div += ref->count;

    }

    r = r / div;

    g = g / div;

    b = b / div;

    return 0xffU<<24 | r<<16 | g<<8 | b;

}

/**

 * Split given box in two at position n. The original box becomes the left part

 * of the split, and the new index box is the right part.

 */

static void split_box(PaletteGenContext *s, struct range_box *box, int n)

{

    struct range_box *new_box = &s->boxes[s->nb_boxes++];

    new_box->start     = n + 1;

    new_box->len       = box->start + box->len - new_box->start;

    new_box->sorted_by = box->sorted_by;

    box->len -= new_box->len;

    av_assert0(box->len     >= 1);

    av_assert0(new_box->len >= 1);

    box->color     = get_avg_color(s->refs, box);

    new_box->color = get_avg_color(s->refs, new_box);

    box->variance     = -1;

    new_box->variance = -1;

}

/**

 * Write the palette into the output frame.

 */

static void write_palette(AVFilterContext *ctx, AVFrame *out)

{

    const PaletteGenContext *s = ctx->priv;

    int x, y, box_id = 0;

    uint32_t *pal = (uint32_t *)out->data[0];

    const int pal_linesize = out->linesize[0] >> 2;

    uint32_t last_color = 0;

    for (y = 0; y < out->height; y++) {

        for (x = 0; x < out->width; x++) {

            if (box_id < s->nb_boxes) {

                pal[x] = s->boxes[box_id++].color;

                if ((x || y) && pal[x] == last_color)

                    av_log(ctx, AV_LOG_WARNING, "Dupped color: %08X\n", pal[x]);

                last_color = pal[x];

            } else {

                pal[x] = 0xff000000; // pad with black

            }

        }

        pal += pal_linesize;

    }

    if (s->reserve_transparent) {

        av_assert0(s->nb_boxes < 256);

        pal[out->width - pal_linesize - 1] = 0x0000ff00; // add a green transparent color

    }

}

/**

 * Crawl the histogram to get all the defined colors, and create a linear list

 * of them (each color reference entry is a pointer to the value in the

 * histogram/hash table).

 */

static struct color_ref **load_color_refs(const struct hist_node *hist, int nb_refs)

{

    int i, j, k = 0;

    struct color_ref **refs = av_malloc_array(nb_refs, sizeof(*refs));

    if (!refs)

        return NULL;

    for (j = 0; j < HIST_SIZE; j++) {

        const struct hist_node *node = &hist[j];

        for (i = 0; i < node->nb_entries; i++)

            refs[k++] = &node->entries[i];

    }

    return refs;

}

static double set_colorquant_ratio_meta(AVFrame *out, int nb_out, int nb_in)

{

    char buf[32];

    const double ratio = (double)nb_out / nb_in;

    snprintf(buf, sizeof(buf), "%f", ratio);

    av_dict_set(&out->metadata, "lavfi.color_quant_ratio", buf, 0);

    return ratio;

}

/**

 * Main function implementing the Median Cut Algorithm defined by Paul Heckbert

 * in Color Image Quantization for Frame Buffer Display (1982)

 */

static AVFrame *get_palette_frame(AVFilterContext *ctx)

{

    AVFrame *out;

    PaletteGenContext *s = ctx->priv;

    AVFilterLink *outlink = ctx->outputs[0];

    double ratio;

    int box_id = 0;

    struct range_box *box;

    /* reference only the used colors from histogram */

    s->refs = load_color_refs(s->histogram, s->nb_refs);

    if (!s->refs) {

        av_log(ctx, AV_LOG_ERROR, "Unable to allocate references for %d different colors\n", s->nb_refs);

        return NULL;

    }

    /* create the palette frame */

    out = ff_get_video_buffer(outlink, outlink->w, outlink->h);

    if (!out)

        return NULL;

    out->pts = 0;

    /* set first box for 0..nb_refs */

    box = &s->boxes[box_id];

    box->len = s->nb_refs;

    box->sorted_by = -1;

    box->color = get_avg_color(s->refs, box);

    box->variance = -1;

    s->nb_boxes = 1;

    while (box && box->len > 1) {

        int i, rr, gr, br, longest;

        uint64_t median, box_weight = 0;

        /* compute the box weight (sum all the weights of the colors in the

         * range) and its boundings */

        uint8_t min[3] = {0xff, 0xff, 0xff};

        uint8_t max[3] = {0x00, 0x00, 0x00};

        for (i = box->start; i < box->start + box->len; i++) {

            const struct color_ref *ref = s->refs[i];

            const uint32_t rgb = ref->color;

            const uint8_t r = rgb >> 16 & 0xff, g = rgb >> 8 & 0xff, b = rgb & 0xff;

            min[0] = FFMIN(r, min[0]), max[0] = FFMAX(r, max[0]);

            min[1] = FFMIN(g, min[1]), max[1] = FFMAX(g, max[1]);

            min[2] = FFMIN(b, min[2]), max[2] = FFMAX(b, max[2]);

            box_weight += ref->count;

        }

        /* define the axis to sort by according to the widest range of colors */

        rr = max[0] - min[0];

        gr = max[1] - min[1];

        br = max[2] - min[2];

        longest = 1; // pick green by default (the color the eye is the most sensitive to)

        if (br >= rr && br >= gr) longest = 2;

        if (rr >= gr && rr >= br) longest = 0;

        if (gr >= rr && gr >= br) longest = 1; // prefer green again

        ff_dlog(ctx, "box #%02X [%6d..%-6d] (%6d) w:%-6"PRIu64" ranges:[%2x %2x %2x] sort by %c (already sorted:%c) ",

                box_id, box->start, box->start + box->len - 1, box->len, box_weight,

                rr, gr, br, "rgb"[longest], box->sorted_by == longest ? 'y':'n');

        /* sort the range by its longest axis if it's not already sorted */

        if (box->sorted_by != longest) {

            cmp_func cmpf = cmp_funcs[longest];

            AV_QSORT(&s->refs[box->start], box->len, const struct color_ref *, cmpf);

            box->sorted_by = longest;

        }

        /* locate the median where to split */

        median = (box_weight + 1) >> 1;

        box_weight = 0;

        /* if you have 2 boxes, the maximum is actually #0: you must have at

         * least 1 color on each side of the split, hence the -2 */

        for (i = box->start; i < box->start + box->len - 2; i++) {

            box_weight += s->refs[i]->count;

            if (box_weight > median)

                break;

        }

        ff_dlog(ctx, "split @ i=%-6d with w=%-6"PRIu64" (target=%6"PRIu64")\n", i, box_weight, median);

        split_box(s, box, i);

        box_id = get_next_box_id_to_split(s);

        box = box_id >= 0 ? &s->boxes[box_id] : NULL;

    }

    ratio = set_colorquant_ratio_meta(out, s->nb_boxes, s->nb_refs);

    av_log(ctx, AV_LOG_INFO, "%d%s colors generated out of %d colors; ratio=%f\n",

           s->nb_boxes, s->reserve_transparent ? "(+1)" : "", s->nb_refs, ratio);

    qsort(s->boxes, s->nb_boxes, sizeof(*s->boxes), cmp_color);

    write_palette(ctx, out);

    return out;

}

/**

 * Hashing function for the color.

 * It keeps the NBITS least significant bit of each component to make it

 * "random" even if the scene doesn't have much different colors.

 */

static inline unsigned color_hash(uint32_t color)

{

    const uint8_t r = color >> 16 & ((1<

    const uint8_t g = color >>  8 & ((1<

    const uint8_t b = color       & ((1<

    return r<<(NBITS*2) | g<

}

/**

 * Locate the color in the hash table and increment its counter.

 */

static int color_inc(struct hist_node *hist, uint32_t color)

{

    int i;

    const unsigned hash = color_hash(color);

    struct hist_node *node = &hist[hash];

    struct color_ref *e;

    for (i = 0; i < node->nb_entries; i++) {

        e = &node->entries[i];

        if (e->color == color) {

            e->count++;

            return 0;

        }

    }

    e = av_dynarray2_add((void**)&node->entries, &node->nb_entries,

                         sizeof(*node->entries), NULL);

    if (!e)

        return AVERROR(ENOMEM);

    e->color = color;

    e->count = 1;

    return 1;

}

/**

 * Update histogram when pixels differ from previous frame.

 */

static int update_histogram_diff(struct hist_node *hist,

                                 const AVFrame *f1, const AVFrame *f2)

{

    int x, y, ret, nb_diff_colors = 0;

    for (y = 0; y < f1->height; y++) {

        const uint32_t *p = (const uint32_t *)(f1->data[0] + y*f1->linesize[0]);

        const uint32_t *q = (const uint32_t *)(f2->data[0] + y*f2->linesize[0]);

        for (x = 0; x < f1->width; x++) {

            if (p[x] == q[x])

                continue;

            ret = color_inc(hist, p[x]);

            if (ret < 0)

                return ret;

            nb_diff_colors += ret;

        }

    }

    return nb_diff_colors;

}

/**

 * Simple histogram of the frame.

 */

static int update_histogram_frame(struct hist_node *hist, const AVFrame *f)

{

    int x, y, ret, nb_diff_colors = 0;

    for (y = 0; y < f->height; y++) {

        const uint32_t *p = (const uint32_t *)(f->data[0] + y*f->linesize[0]);

        for (x = 0; x < f->width; x++) {

            ret = color_inc(hist, p[x]);

            if (ret < 0)

                return ret;

            nb_diff_colors += ret;

        }

    }

    return nb_diff_colors;

}

/**

 * Update the histogram for each passing frame. No frame will be pushed here.

 */

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

{

    AVFilterContext *ctx = inlink->dst;

    PaletteGenContext *s = ctx->priv;

    const int ret = s->prev_frame ? update_histogram_diff(s->histogram, s->prev_frame, in)

                                  : update_histogram_frame(s->histogram, in);

    if (ret > 0)

        s->nb_refs += ret;

    if (s->stats_mode == STATS_MODE_DIFF_FRAMES) {

        av_frame_free(&s->prev_frame);

        s->prev_frame = in;

    } else {

        av_frame_free(&in);

    }

    return ret;

}

/**

 * Returns only one frame at the end containing the full palette.

 */

static int request_frame(AVFilterLink *outlink)

{

    AVFilterContext *ctx = outlink->src;

    AVFilterLink *inlink = ctx->inputs[0];

    PaletteGenContext *s = ctx->priv;

    int r;

    r = ff_request_frame(inlink);

    if (r == AVERROR_EOF && !s->palette_pushed && s->nb_refs) {

        r = ff_filter_frame(outlink, get_palette_frame(ctx));

        s->palette_pushed = 1;

        return r;

    }

    return r;

}

/**

 * The output is one simple 16x16 squared-pixels palette.

 */

static int config_output(AVFilterLink *outlink)

{

    outlink->w = outlink->h = 16;

    outlink->sample_aspect_ratio = av_make_q(1, 1);

    outlink->flags |= FF_LINK_FLAG_REQUEST_LOOP;

    return 0;

}

static av_cold void uninit(AVFilterContext *ctx)

{

    int i;

    PaletteGenContext *s = ctx->priv;

    for (i = 0; i < HIST_SIZE; i++)

        av_freep(&s->histogram[i].entries);

    av_freep(&s->refs);

    av_frame_free(&s->prev_frame);

}

static const AVFilterPad palettegen_inputs[] = {

    {

        .name         = "default",

        .type         = AVMEDIA_TYPE_VIDEO,

        .filter_frame = filter_frame,

    },

    { NULL }

};

static const AVFilterPad palettegen_outputs[] = {

    {

        .name          = "default",

        .type          = AVMEDIA_TYPE_VIDEO,

        .config_props  = config_output,

        .request_frame = request_frame,

    },

    { NULL }

};

AVFilter ff_vf_palettegen = {

    .name          = "palettegen",

    .description   = NULL_IF_CONFIG_SMALL("Find the optimal palette for a given stream."),

    .priv_size     = sizeof(PaletteGenContext),

    .uninit        = uninit,

    .query_formats = query_formats,

    .inputs        = palettegen_inputs,

    .outputs       = palettegen_outputs,

    .priv_class    = &palettegen_class,

};