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35
libpng.txt
35
libpng.txt
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libpng.txt - A description on how to use and modify libpng
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libpng version 1.0.6j - May 4, 2000
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libpng version 1.0.7beta11 - May 6, 2000
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Updated and distributed by Glenn Randers-Pehrson
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<randeg@alum.rpi.edu>
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Copyright (c) 1998, 1999, 2000 Glenn Randers-Pehrson
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@@ -94,9 +94,20 @@ The png_info structure is designed to provide information about the
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PNG file. At one time, the fields of png_info were intended to be
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directly accessible to the user. However, this tended to cause problems
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with applications using dynamically loaded libraries, and as a result
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a set of interface functions for png_info was developed. The fields
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of png_info are still available for older applications, but it is
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suggested that applications use the new interfaces if at all possible.
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a set of interface functions for png_info (the png_get_*() and png_set_*()
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functions) was developed. The fields of png_info are still available for
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older applications, but it is suggested that applications use the new
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interfaces if at all possible.
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Applications that do make direct access to the members of png_struct (except
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for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
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and applications that make direct access to the members of png_info must
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be recompiled if they were compiled or loaded with libpng version 1.0.6,
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in which the members were in a different order. In version 1.0.7, the
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members of the png_info structure reverted to the old order, as they were
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in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
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structures are going to be hidden, and the contents of the structures will
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only be accessible through the png_get/png_set functions.
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The png.h header file is an invaluable reference for programming with libpng.
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And while I'm on the topic, make sure you include the libpng header file:
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@@ -2538,8 +2549,10 @@ still alive and well, but they have moved on to other things.
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The old libpng functions png_read_init(), png_write_init(),
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png_info_init(), png_read_destroy(), and png_write_destory() have been
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moved to PNG_INTERNAL in version 0.95 to discourage their use. The
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preferred method of creating and initializing the libpng structures is
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moved to PNG_INTERNAL in version 0.95 to discourage their use. These
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functions will be removed from libpng version 2.0.0.
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The preferred method of creating and initializing the libpng structures is
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via the png_create_read_struct(), png_create_write_struct(), and
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png_create_info_struct() because they isolate the size of the structures
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from the application, allow version error checking, and also allow the
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@@ -2556,19 +2569,19 @@ png_read_init() as was suggested in libpng-0.88 is no longer supported
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because this caused applications that do not use custom error functions
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to fail if the png_ptr was not initialized to zero. It is still possible
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to set the error callbacks AFTER png_read_init(), or to change them with
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png_set_error_fn(), which is essentially the same function, but with a
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new name to force compilation errors with applications that try to use
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the old method.
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png_set_error_fn(), which is essentially the same function, but with a new
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name to force compilation errors with applications that try to use the old
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method.
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VII. Y2K Compliance in libpng
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May 4, 2000
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May 6, 2000
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Since the PNG Development group is an ad-hoc body, we can't make
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an official declaration.
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This is your unofficial assurance that libpng from version 0.71 and
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upward through 1.0.6j are Y2K compliant. It is my belief that earlier
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upward through 1.0.7beta11 are Y2K compliant. It is my belief that earlier
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versions were also Y2K compliant.
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Libpng only has three year fields. One is a 2-byte unsigned integer that
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