1/*
2 * Microsoft Screen 1 (aka Windows Media Video V7 Screen) decoder
3 * Copyright (c) 2012 Konstantin Shishkov
4 *
5 * This file is part of FFmpeg.
6 *
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22/**
23 * @file
24 * Microsoft Screen 1 (aka Windows Media Video V7 Screen) decoder
25 */
26
27#include "avcodec.h"
28#include "internal.h"
29#include "mss12.h"
30
31typedef struct MSS1Context {
32    MSS12Context   ctx;
33    AVFrame       *pic;
34    SliceContext   sc;
35} MSS1Context;
36
37static void arith_normalise(ArithCoder *c)
38{
39    for (;;) {
40        if (c->high >= 0x8000) {
41            if (c->low < 0x8000) {
42                if (c->low >= 0x4000 && c->high < 0xC000) {
43                    c->value -= 0x4000;
44                    c->low   -= 0x4000;
45                    c->high  -= 0x4000;
46                } else {
47                    return;
48                }
49            } else {
50                c->value -= 0x8000;
51                c->low   -= 0x8000;
52                c->high  -= 0x8000;
53            }
54        }
55        c->value <<= 1;
56        c->low   <<= 1;
57        c->high  <<= 1;
58        c->high   |= 1;
59        c->value  |= get_bits1(c->gbc.gb);
60    }
61}
62
63ARITH_GET_BIT(arith)
64
65static int arith_get_bits(ArithCoder *c, int bits)
66{
67    int range = c->high - c->low + 1;
68    int val   = (((c->value - c->low + 1) << bits) - 1) / range;
69    int prob  = range * val;
70
71    c->high   = ((prob + range) >> bits) + c->low - 1;
72    c->low   += prob >> bits;
73
74    arith_normalise(c);
75
76    return val;
77}
78
79static int arith_get_number(ArithCoder *c, int mod_val)
80{
81    int range = c->high - c->low + 1;
82    int val   = ((c->value - c->low + 1) * mod_val - 1) / range;
83    int prob  = range * val;
84
85    c->high   = (prob + range) / mod_val + c->low - 1;
86    c->low   += prob / mod_val;
87
88    arith_normalise(c);
89
90    return val;
91}
92
93static int arith_get_prob(ArithCoder *c, int16_t *probs)
94{
95    int range = c->high - c->low + 1;
96    int val   = ((c->value - c->low + 1) * probs[0] - 1) / range;
97    int sym   = 1;
98
99    while (probs[sym] > val)
100        sym++;
101
102    c->high = range * probs[sym - 1] / probs[0] + c->low - 1;
103    c->low += range * probs[sym]     / probs[0];
104
105    return sym;
106}
107
108ARITH_GET_MODEL_SYM(arith)
109
110static void arith_init(ArithCoder *c, GetBitContext *gb)
111{
112    c->low           = 0;
113    c->high          = 0xFFFF;
114    c->value         = get_bits(gb, 16);
115    c->gbc.gb        = gb;
116    c->get_model_sym = arith_get_model_sym;
117    c->get_number    = arith_get_number;
118}
119
120static int decode_pal(MSS12Context *ctx, ArithCoder *acoder)
121{
122    int i, ncol, r, g, b;
123    uint32_t *pal = ctx->pal + 256 - ctx->free_colours;
124
125    if (!ctx->free_colours)
126        return 0;
127
128    ncol = arith_get_number(acoder, ctx->free_colours + 1);
129    for (i = 0; i < ncol; i++) {
130        r = arith_get_bits(acoder, 8);
131        g = arith_get_bits(acoder, 8);
132        b = arith_get_bits(acoder, 8);
133        *pal++ = (0xFFU << 24) | (r << 16) | (g << 8) | b;
134    }
135
136    return !!ncol;
137}
138
139static int mss1_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
140                             AVPacket *avpkt)
141{
142    MSS1Context *ctx = avctx->priv_data;
143    MSS12Context *c = &ctx->ctx;
144    GetBitContext gb;
145    ArithCoder acoder;
146    int pal_changed = 0;
147    int ret;
148
149    if ((ret = init_get_bits8(&gb, avpkt->data, avpkt->size)) < 0)
150        return ret;
151
152    arith_init(&acoder, &gb);
153
154    if ((ret = ff_reget_buffer(avctx, ctx->pic)) < 0)
155        return ret;
156
157    c->pal_pic    =  ctx->pic->data[0] + ctx->pic->linesize[0] * (avctx->height - 1);
158    c->pal_stride = -ctx->pic->linesize[0];
159    c->keyframe   = !arith_get_bit(&acoder);
160    if (c->keyframe) {
161        c->corrupted = 0;
162        ff_mss12_slicecontext_reset(&ctx->sc);
163        pal_changed        = decode_pal(c, &acoder);
164        ctx->pic->key_frame = 1;
165        ctx->pic->pict_type = AV_PICTURE_TYPE_I;
166    } else {
167        if (c->corrupted)
168            return AVERROR_INVALIDDATA;
169        ctx->pic->key_frame = 0;
170        ctx->pic->pict_type = AV_PICTURE_TYPE_P;
171    }
172    c->corrupted = ff_mss12_decode_rect(&ctx->sc, &acoder, 0, 0,
173                                        avctx->width, avctx->height);
174    if (c->corrupted)
175        return AVERROR_INVALIDDATA;
176    memcpy(ctx->pic->data[1], c->pal, AVPALETTE_SIZE);
177    ctx->pic->palette_has_changed = pal_changed;
178
179    if ((ret = av_frame_ref(data, ctx->pic)) < 0)
180        return ret;
181
182    *got_frame      = 1;
183
184    /* always report that the buffer was completely consumed */
185    return avpkt->size;
186}
187
188static av_cold int mss1_decode_init(AVCodecContext *avctx)
189{
190    MSS1Context * const c = avctx->priv_data;
191    int ret;
192
193    c->ctx.avctx       = avctx;
194
195    c->pic = av_frame_alloc();
196    if (!c->pic)
197        return AVERROR(ENOMEM);
198
199    ret = ff_mss12_decode_init(&c->ctx, 0, &c->sc, NULL);
200
201    avctx->pix_fmt = AV_PIX_FMT_PAL8;
202
203    return ret;
204}
205
206static av_cold int mss1_decode_end(AVCodecContext *avctx)
207{
208    MSS1Context * const ctx = avctx->priv_data;
209
210    av_frame_free(&ctx->pic);
211    ff_mss12_decode_end(&ctx->ctx);
212
213    return 0;
214}
215
216AVCodec ff_mss1_decoder = {
217    .name           = "mss1",
218    .long_name      = NULL_IF_CONFIG_SMALL("MS Screen 1"),
219    .type           = AVMEDIA_TYPE_VIDEO,
220    .id             = AV_CODEC_ID_MSS1,
221    .priv_data_size = sizeof(MSS1Context),
222    .init           = mss1_decode_init,
223    .close          = mss1_decode_end,
224    .decode         = mss1_decode_frame,
225    .capabilities   = CODEC_CAP_DR1,
226};
227