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tIME and text position handling

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The handling of tIME and text chunks on read now records the location of the
chunks relative to PLTE and IDAT.  Behavior on write is unchanged except that if
the position was recorded on read it will be re-used.

This involves an ABI change to the png_text_struct; a one byte location field is
added (with the same meaning as the one used to record unknown chunk location.)
Because this field is only used on read there is no API change unless a png_info
from a libpng read is passed to a subsequent libpng write (this did not work
very well before 1.7; the tIME chunk could get duplicated.)

png_set_text ignores the new field, resetting it to the current position in the
read or write stream.  On write the position is set to the next location to be
written unless the write has not started (the position is before the signature)
in which case the location is set to PNG_HAVE_PLTE|PNG_AFTER_IDAT.  When the
chunk is written the position is set to the actual write location (effectively
the position is frozen.)

Signed-off-by: John Bowler <jbowler@acm.org>
This commit is contained in:
John Bowler
2015-12-29 15:30:31 -08:00
parent c90572ee77
commit 4253c4d759
7 changed files with 192 additions and 84 deletions
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160
pngwrite.c
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@@ -72,6 +72,75 @@ write_unknown_chunks(png_structrp png_ptr, png_const_inforp info_ptr,
}
#endif /* WRITE_UNKNOWN_CHUNKS */
#ifdef PNG_WRITE_TEXT_SUPPORTED
static void
png_write_text(png_structrp png_ptr, png_const_inforp info_ptr, png_byte where)
/* Text chunk helper */
{
int i;
/* Check to see if we need to write text chunks */
for (i = 0; i < info_ptr->num_text; i++)
{
png_debug2(2, "Writing text chunk %d, type %d", i,
info_ptr->text[i].compression);
/* Text chunks are written at info_ptr->text[i].location, skip the chunk
* if we are not writing at that location:
*/
if ((info_ptr->text[i].location & where) == 0U)
continue;
switch (info_ptr->text[i].compression)
{
case PNG_ITXT_COMPRESSION_NONE:
case PNG_ITXT_COMPRESSION_zTXt:
# ifdef PNG_WRITE_iTXt_SUPPORTED
/* Write international chunk */
png_write_iTXt(png_ptr, info_ptr->text[i].compression,
info_ptr->text[i].key, info_ptr->text[i].lang,
info_ptr->text[i].lang_key, info_ptr->text[i].text);
# else /* !WRITE_iTXT */
png_app_error(png_ptr, "Unable to write international text");
# endif /* !WRITE_iTXT */
break;
case PNG_TEXT_COMPRESSION_zTXt:
# ifdef PNG_WRITE_zTXt_SUPPORTED
/* Write compressed chunk */
png_write_zTXt(png_ptr, info_ptr->text[i].key,
info_ptr->text[i].text, info_ptr->text[i].compression);
# else /* !WRITE_zTXT */
png_app_error(png_ptr, "Unable to write compressed text");
# endif /* !WRITE_zTXT */
break;
case PNG_TEXT_COMPRESSION_NONE:
# ifdef PNG_WRITE_tEXt_SUPPORTED
/* Write uncompressed chunk */
png_write_tEXt(png_ptr, info_ptr->text[i].key,
info_ptr->text[i].text, 0);
# else /* !WRITE_tEXt */
/* Can't get here TODO: why not? */
png_app_error(png_ptr, "Unable to write uncompressed text");
# endif /* !WRITE_tEXt */
break;
default:
/* This is an internal error because the libpng checking should
* never manage to set any 'compression' except the above values.
*/
impossible("invalid text compression");
}
/* The chunk was written, record where. This allows the location to have
* multiple bits set, the first successful write freezes the location.
*/
info_ptr->text[i].location = where;
}
}
#endif /* WRITE_TEXT */
/* Writes all the PNG information. This is the suggested way to use the
* library. If you have a new chunk to add, make a function to write it,
* and put it in the correct location here. If you want the chunk written
@@ -138,6 +207,12 @@ png_write_info_before_PLTE(png_structrp png_ptr, png_const_inforp info_ptr)
* the application continues writing the PNG. So check the 'invalid'
* flag here too.
*/
# ifdef PNG_WRITE_tIME_SUPPORTED
if ((info_ptr->valid & PNG_INFO_tIME) != 0 &&
(info_ptr->time_location & PNG_HAVE_IHDR) != 0)
png_write_tIME(png_ptr, &(info_ptr->mod_time));
# endif /* WRITE_tIME */
# ifdef PNG_WRITE_gAMA_SUPPORTED /* enables GAMMA */
if ((info_ptr->colorspace.flags & PNG_COLORSPACE_INVALID) == 0 &&
(info_ptr->colorspace.flags & PNG_COLORSPACE_FROM_gAMA) != 0 &&
@@ -194,6 +269,11 @@ png_write_info_before_PLTE(png_structrp png_ptr, png_const_inforp info_ptr)
png_write_cHRM_fixed(png_ptr, &info_ptr->colorspace.end_points_xy);
# endif /* WRITE_cHRM */
# ifdef PNG_WRITE_TEXT_SUPPORTED
if (info_ptr->num_text > 0)
png_write_text(png_ptr, info_ptr, PNG_HAVE_IHDR);
# endif /* WRITE_TEXT */
# ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
/* The third arugment must encode only one bit, otherwise chunks will
* be written twice because the test in write_unknown_chunks is
@@ -208,71 +288,6 @@ png_write_info_before_PLTE(png_structrp png_ptr, png_const_inforp info_ptr)
"png_write_info_before_PLTE called more than once");
}
#ifdef PNG_WRITE_TEXT_SUPPORTED
static void
png_write_text(png_structrp png_ptr, png_const_inforp info_ptr)
/* Text chunk helper */
{
int i;
/* Check to see if we need to write text chunks */
for (i = 0; i < info_ptr->num_text; i++)
{
png_debug2(2, "Writing text chunk %d, type %d", i,
info_ptr->text[i].compression);
/* An internationalized chunk? */
if (info_ptr->text[i].compression > 0)
{
# ifdef PNG_WRITE_iTXt_SUPPORTED
/* Write international chunk */
png_write_iTXt(png_ptr, info_ptr->text[i].compression,
info_ptr->text[i].key, info_ptr->text[i].lang,
info_ptr->text[i].lang_key, info_ptr->text[i].text);
# else /* !WRITE_iTXT */
png_app_error(png_ptr, "Unable to write international text");
# endif /* !WRITE_iTXT */
/* Mark this chunk as written */
if (info_ptr->text[i].compression == PNG_TEXT_COMPRESSION_NONE)
info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_NONE_WR;
else
info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_zTXt_WR;
}
/* If we want a compressed text chunk */
else if (info_ptr->text[i].compression == PNG_TEXT_COMPRESSION_zTXt)
{
# ifdef PNG_WRITE_zTXt_SUPPORTED
/* Write compressed chunk */
png_write_zTXt(png_ptr, info_ptr->text[i].key,
info_ptr->text[i].text, info_ptr->text[i].compression);
# else /* !WRITE_zTXT */
png_app_error(png_ptr, "Unable to write compressed text");
# endif /* !WRITE_zTXT */
/* Mark this chunk as written */
info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_zTXt_WR;
}
else if (info_ptr->text[i].compression == PNG_TEXT_COMPRESSION_NONE)
{
# ifdef PNG_WRITE_tEXt_SUPPORTED
/* Write uncompressed chunk */
png_write_tEXt(png_ptr, info_ptr->text[i].key,
info_ptr->text[i].text, 0);
# else /* !WRITE_tEXt */
/* Can't get here TODO: why not? */
png_app_error(png_ptr, "Unable to write uncompressed text");
# endif /* !WRITE_tEXt */
/* Mark this chunk as written */
info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_NONE_WR;
}
}
}
#endif /* WRITE_TEXT */
void PNGAPI
png_write_info(png_structrp png_ptr, png_const_inforp info_ptr)
{
@@ -303,6 +318,11 @@ png_write_info(png_structrp png_ptr, png_const_inforp info_ptr)
png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
png_error(png_ptr, "Valid palette required for paletted images");
/* But always set the mode flag because without this we don't know when to
* write the post-palette text or unknown chunks.
*/
png_ptr->mode |= PNG_HAVE_PLTE;
# ifdef PNG_WRITE_tRNS_SUPPORTED
if ((info_ptr->valid & PNG_INFO_tRNS) !=0)
{
@@ -349,7 +369,8 @@ png_write_info(png_structrp png_ptr, png_const_inforp info_ptr)
# endif /* WRITE_pHYs */
# ifdef PNG_WRITE_tIME_SUPPORTED
if ((info_ptr->valid & PNG_INFO_tIME) != 0)
if ((info_ptr->valid & PNG_INFO_tIME) != 0 &&
(info_ptr->time_location & PNG_HAVE_PLTE) != 0)
png_write_tIME(png_ptr, &(info_ptr->mod_time));
# endif /* WRITE_tIME */
@@ -365,7 +386,7 @@ png_write_info(png_structrp png_ptr, png_const_inforp info_ptr)
# ifdef PNG_WRITE_TEXT_SUPPORTED
if (info_ptr->num_text > 0)
png_write_text(png_ptr, info_ptr);
png_write_text(png_ptr, info_ptr, PNG_HAVE_PLTE);
# endif /* WRITE_TEXT */
# ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
@@ -438,13 +459,14 @@ png_write_end(png_structrp png_ptr, png_inforp info_ptr)
{
# ifdef PNG_WRITE_tIME_SUPPORTED
/* Check to see if user has supplied a time chunk */
if ((info_ptr->valid & PNG_INFO_tIME) != 0)
if ((info_ptr->valid & PNG_INFO_tIME) != 0 &&
(info_ptr->time_location & PNG_AFTER_IDAT) != 0)
png_write_tIME(png_ptr, &(info_ptr->mod_time));
# endif
# ifdef PNG_WRITE_TEXT_SUPPORTED
if (info_ptr->num_text > 0)
png_write_text(png_ptr, info_ptr);
png_write_text(png_ptr, info_ptr, PNG_AFTER_IDAT);
# endif /* WRITE_TEXT */
# ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED