[FFmpeg-devel] [PATCH] avcodec: add ARBC decoder

[Michael Niedermayer]

On Tue, Jan 22, 2019 at 10:55:33AM +0100, Paul B Mahol wrote:
> Thanks Kostya for great help in reversing binary.
> 
> Signed-off-by: Paul B Mahol <onemda at gmail.com>
> ---
>  libavcodec/Makefile     |   1 +
>  libavcodec/allcodecs.c  |   1 +
>  libavcodec/arbc.c       | 203 ++++++++++++++++++++++++++++++++++++++++
>  libavcodec/avcodec.h    |   1 +
>  libavcodec/codec_desc.c |   7 ++
>  libavformat/riff.c      |   1 +
>  6 files changed, 214 insertions(+)
>  create mode 100644 libavcodec/arbc.c
> 
> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
> index bf746c143d..8e240aecf0 100644
> --- a/libavcodec/Makefile
> +++ b/libavcodec/Makefile
> @@ -198,6 +198,7 @@ OBJS-$(CONFIG_APTX_HD_DECODER)         += aptx.o
>  OBJS-$(CONFIG_APTX_HD_ENCODER)         += aptx.o
>  OBJS-$(CONFIG_APNG_DECODER)            += png.o pngdec.o pngdsp.o
>  OBJS-$(CONFIG_APNG_ENCODER)            += png.o pngenc.o
> +OBJS-$(CONFIG_ARBC_DECODER)            += arbc.o
>  OBJS-$(CONFIG_SSA_DECODER)             += assdec.o ass.o
>  OBJS-$(CONFIG_SSA_ENCODER)             += assenc.o ass.o
>  OBJS-$(CONFIG_ASS_DECODER)             += assdec.o ass.o
> diff --git a/libavcodec/allcodecs.c b/libavcodec/allcodecs.c
> index fe0376e27e..5cbb09a5a4 100644
> --- a/libavcodec/allcodecs.c
> +++ b/libavcodec/allcodecs.c
> @@ -41,6 +41,7 @@ extern AVCodec ff_anm_decoder;
>  extern AVCodec ff_ansi_decoder;
>  extern AVCodec ff_apng_encoder;
>  extern AVCodec ff_apng_decoder;
> +extern AVCodec ff_arbc_decoder;
>  extern AVCodec ff_asv1_encoder;
>  extern AVCodec ff_asv1_decoder;
>  extern AVCodec ff_asv2_encoder;
> diff --git a/libavcodec/arbc.c b/libavcodec/arbc.c
> new file mode 100644
> index 0000000000..59a1d7bf0a
> --- /dev/null
> +++ b/libavcodec/arbc.c
> @@ -0,0 +1,203 @@
> +/*
> + * Gryphon's Anim Compressor decoder
> + * Copyright (c) 2018 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 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
> + */
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +
> +#include "libavutil/imgutils.h"
> +#include "libavutil/internal.h"
> +#include "libavutil/intreadwrite.h"
> +#include "libavutil/mem.h"
> +
> +#include "avcodec.h"
> +#include "bytestream.h"
> +#include "internal.h"
> +
> +typedef struct ARBCContext {
> +    GetByteContext gb;
> +
> +    AVFrame *prev_frame;
> +} ARBCContext;
> +
> +static void fill_tile4(AVCodecContext *avctx, uint8_t *color, AVFrame *frame)
> +{
> +    ARBCContext *s = avctx->priv_data;
> +    GetByteContext *gb = &s->gb;
> +    int nb_tiles = bytestream2_get_le16(gb);
> +    int h = avctx->height - 1;
> +
> +    for (int i = 0; i < nb_tiles; i++) {
> +        int y = bytestream2_get_byte(gb);
> +        int x = bytestream2_get_byte(gb);
> +        uint16_t mask = bytestream2_get_le16(gb);
> +        int start_y = y * 4, start_x = x * 4;
> +        int end_y = start_y + 4, end_x = start_x + 4;
> +
> +        for (int j = start_y; j < end_y; j++) {
> +            for (int k = start_x; k < end_x; k++) {
> +                if (mask & 0x8000) {
> +                    if (j >= avctx->height || k >= avctx->width)
> +                        continue;

this would treat 1 bits differently than 0 bits when they are outside
teh frame. That is 1 bits would not advance in the bitstream (aka not execute 
mask = mask << 1;
this also differs from fill_tileX()
is that intended ?

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When the tyrant has disposed of foreign enemies by conquest or treaty, and
there is nothing more to fear from them, then he is always stirring up
some war or other, in order that the people may require a leader. -- Plato
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