/src/ffmpeg/libavcodec/mss12.h

Source
/*
 * Copyright (c) 2012 Konstantin Shishkov
 *
 * 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
 * Common header for Microsoft Screen 1 and 2
 */

#ifndef AVCODEC_MSS12_H
#define AVCODEC_MSS12_H

#include "libavutil/intreadwrite.h"
#include "avcodec.h"
#include "get_bits.h"
#include "bytestream.h"

#define MODEL_MIN_SYMS    2
#define MODEL_MAX_SYMS  256
#define THRESH_ADAPTIVE  -1
#define THRESH_LOW       15
#define THRESH_HIGH      50

typedef struct Model {
    int16_t cum_prob[MODEL_MAX_SYMS + 1];
    int16_t weights[MODEL_MAX_SYMS + 1];
    uint8_t idx2sym[MODEL_MAX_SYMS + 1];
    int num_syms;
    int thr_weight, threshold;
} Model;

typedef struct ArithCoder {
    int low, high, value;
    int overread;
#define MAX_OVERREAD 16
    union {
        GetBitContext *gb;
        GetByteContext *gB;
    } gbc;
    int (*get_model_sym)(struct ArithCoder *c, Model *m);
    int (*get_number)   (struct ArithCoder *c, int n);
} ArithCoder;

typedef struct PixContext {
    int cache_size, num_syms;
    uint8_t cache[12];
    Model cache_model, full_model;
    Model sec_models[15][4];
    int special_initial_cache;
} PixContext;

struct MSS12Context;

typedef struct SliceContext {
    const struct MSS12Context *c;
    Model      intra_region, inter_region;
    Model      pivot, edge_mode, split_mode;
    PixContext intra_pix_ctx, inter_pix_ctx;
} SliceContext;

typedef struct MSS12Context {
    AVCodecContext *avctx;
    uint32_t       pal[256];
    uint8_t        *pal_pic;
    uint8_t        *last_pal_pic;
    ptrdiff_t      pal_stride;
    uint8_t        *mask;
    ptrdiff_t      mask_stride;
    uint8_t        *rgb_pic;
    uint8_t        *last_rgb_pic;
    ptrdiff_t      rgb_stride;
    int            free_colours;
    int            keyframe;
    int            mvX, mvY;
    int            corrupted;
    int            slice_split;
    int            full_model_syms;
} MSS12Context;

int ff_mss12_decode_rect(SliceContext *ctx, ArithCoder *acoder,
                         int x, int y, int width, int height);
void ff_mss12_model_update(Model *m, int val);
void ff_mss12_slicecontext_reset(SliceContext *sc);
int ff_mss12_decode_init(MSS12Context *c, int version,
                         SliceContext *sc1, SliceContext *sc2);
int ff_mss12_decode_end(MSS12Context *ctx);

#define ARITH_GET_BIT(prefix)                                           \
static int prefix ## _get_bit(ArithCoder *c)                            \
{                                                                       \
    int range = c->high - c->low + 1;                                   \
    int bit   = 2 * c->value - c->low >= c->high;                       \
                                                                        \
    if (bit)                                                            \
        c->low += range >> 1;                                           \
    else                                                                \
        c->high = c->low + (range >> 1) - 1;                            \
                                                                        \
    prefix ## _normalise(c);                                            \
                                                                        \
    return bit;                                                         \
}

#define ARITH_GET_MODEL_SYM(prefix)                                     \
static int prefix ## _get_model_sym(ArithCoder *c, Model *m)            \
{                                                                       \
    int idx, val;                                                       \
                                                                        \
    idx = prefix ## _get_prob(c, m->cum_prob);                          \
                                                                        \
    val = m->idx2sym[idx];                                              \
    ff_mss12_model_update(m, idx);                                      \
                                                                        \
    prefix ## _normalise(c);                                            \
                                                                        \
    return val;                                                         \
}

#endif /* AVCODEC_MSS12_H */

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Created: 2026-05-16 07:49