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ffmpeg / libavcodec / rle.c @ 2912e87a

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/*
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 * RLE encoder
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 * Copyright (c) 2007 Bobby Bingham
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 *
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 * This file is part of Libav.
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 *
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 * Libav is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * Libav is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with Libav; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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#include "avcodec.h"
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#include "rle.h"
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/**
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 * Count up to 127 consecutive pixels which are either all the same or
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 * all differ from the previous and next pixels.
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 * @param start Pointer to the first pixel
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 * @param len Maximum number of pixels
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 * @param bpp Bytes per pixel
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 * @param same 1 if searching for identical pixel values.  0 for differing
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 * @return Number of matching consecutive pixels found
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 */
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static int count_pixels(const uint8_t *start, int len, int bpp, int same)
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{
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    const uint8_t *pos;
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    int count = 1;
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    for(pos = start + bpp; count < FFMIN(127, len); pos += bpp, count ++) {
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        if(same != !memcmp(pos-bpp, pos, bpp)) {
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            if(!same) {
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                /* if bpp == 1, then 0 1 1 0 is more efficiently encoded as a single
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                 * raw block of pixels.  for larger bpp, RLE is as good or better */
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                if(bpp == 1 && count + 1 < FFMIN(127, len) && *pos != *(pos+1))
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                    continue;
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                /* if RLE can encode the next block better than as a raw block,
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                 * back up and leave _all_ the identical pixels for RLE */
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                count --;
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            }
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            break;
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        }
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    }
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    return count;
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}
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int ff_rle_encode(uint8_t *outbuf, int out_size, const uint8_t *ptr , int bpp, int w,
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                  int add_rep, int xor_rep, int add_raw, int xor_raw)
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{
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    int count, x;
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    uint8_t *out = outbuf;
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    for(x = 0; x < w; x += count) {
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        /* see if we can encode the next set of pixels with RLE */
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        if((count = count_pixels(ptr, w-x, bpp, 1)) > 1) {
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            if(out + bpp + 1 > outbuf + out_size) return -1;
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            *out++ = (count ^ xor_rep) + add_rep;
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            memcpy(out, ptr, bpp);
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            out += bpp;
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        } else {
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            /* fall back on uncompressed */
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            count = count_pixels(ptr, w-x, bpp, 0);
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            if(out + bpp*count >= outbuf + out_size) return -1;
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            *out++ = (count ^ xor_raw) + add_raw;
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            memcpy(out, ptr, bpp * count);
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            out += bpp * count;
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        }
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        ptr += count * bpp;
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    }
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    return out - outbuf;
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}