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https://git.code.sf.net/p/libpng/code.git
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149 lines
3.5 KiB
C
149 lines
3.5 KiB
C
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/* pngwtran.c - transforms the data in a row for PNG writers
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*
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* Last changed in libpng 1.6.17 [(PENDING RELEASE)]
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* Copyright (c) 1998-2002,2004,2006-2015 Glenn Randers-Pehrson
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* (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
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* (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
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*
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* This code is released under the libpng license.
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* For conditions of distribution and use, see the disclaimer
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* and license in png.h
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*/
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#include "pngpriv.h"
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#define PNG_SRC_FILE PNG_SRC_FILE_pngwtran
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#ifdef PNG_WRITE_PACK_SUPPORTED
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/* Pack pixels into bytes. */
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static void
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png_do_write_pack(png_transformp *transform, png_transform_controlp tc)
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{
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png_alloc_size_t rowbytes = PNG_TC_ROWBYTES(*tc);
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png_const_bytep sp = png_voidcast(png_const_bytep, tc->sp);
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png_const_bytep ep = png_upcast(png_const_bytep, tc->sp) + rowbytes;
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png_bytep dp = png_voidcast(png_bytep, tc->dp);
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png_debug(1, "in png_do_pack");
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# define png_ptr tc->png_ptr
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switch ((*transform)->args)
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{
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case 1:
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{
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unsigned int mask = 0x80, v = 0;
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while (sp < ep)
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{
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if (*sp++ != 0)
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v |= mask;
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mask >>= 1;
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if (mask == 0)
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{
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mask = 0x80;
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*dp++ = PNG_BYTE(v);
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v = 0;
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}
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}
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if (mask != 0x80)
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*dp++ = PNG_BYTE(v);
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break;
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}
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case 2:
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{
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unsigned int shift = 8, v = 0;
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while (sp < ep)
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{
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shift -= 2;
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v |= (*sp++ & 0x3) << shift;
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if (shift == 0)
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{
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shift = 8;
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*dp++ = PNG_BYTE(v);
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v = 0;
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}
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}
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if (shift != 8)
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*dp++ = PNG_BYTE(v);
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break;
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}
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case 4:
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{
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unsigned int shift = 8, v = 0;
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while (sp < ep)
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{
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shift -= 4;
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v |= ((*sp++ & 0xf) << shift);
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if (shift == 0)
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{
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shift = 8;
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*dp++ = PNG_BYTE(v);
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v = 0;
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}
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}
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if (shift != 8)
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*dp++ = PNG_BYTE(v);
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break;
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}
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default:
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impossible("bit depth");
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}
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if ((tc->format & PNG_FORMAT_FLAG_COLORMAP) == 0 &&
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--(tc->range) == 0)
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tc->format &= PNG_BIC_MASK(PNG_FORMAT_FLAG_RANGE);
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tc->bit_depth = (*transform)->args;
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tc->sp = tc->dp;
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# undef png_ptr
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}
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void /* PRIVATE */
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png_init_write_pack(png_transformp *transform, png_transform_controlp tc)
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{
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# define png_ptr tc->png_ptr
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debug(tc->init);
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# undef png_ptr
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/* The init routine is called *forward* so the transform control we get has
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* the required bit depth and the transform routine will increase it to 8
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* bits per channel. The code doesn't really care how many channels there
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* are, but the only way to get a channel depth of less than 8 is to have
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* just one channel.
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*/
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if (tc->bit_depth < 8) /* else no packing/unpacking */
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{
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if (tc->init == PNG_TC_INIT_FINAL)
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{
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(*transform)->fn = png_do_write_pack;
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/* Record this for the backwards run: */
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(*transform)->args = tc->bit_depth & 0xf;
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}
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if ((tc->format & PNG_FORMAT_FLAG_COLORMAP) == 0)
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{
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tc->range++;
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tc->format |= PNG_FORMAT_FLAG_RANGE; /* forwards: backwards cancels */
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}
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tc->bit_depth = 8;
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}
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else /* the transform is not applicable */
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(*transform)->fn = NULL;
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}
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#endif /* WRITE_PACK */
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