[devel] Freeze build-time only configuration in the build.

In all prior versions of libpng most configuration options
    controlled by compiler #defines had to be repeated by the
    application code that used libpng.  This patch changes this
    so that compilation options that can only be changed at build
    time are frozen in the build.  Options that are compiler
    dependent (and those that are system dependent) are evaluated
    each time - pngconf.h holds these.  Options that can be changed
    per-file in the application are in png.h.  Frozen options are
    in the new installed header file pnglconf.h

pngpriv.h

@@ -30,12 +30,18 @@
 #include "pngstruct.h"
 
 #include <stdlib.h>
+#ifdef BSD
+#  include <strings.h>
+#else
+#  include <string.h>
+#endif
 
 /* Added at libpng-1.2.9 */
 /* Moved to pngpriv.h at libpng-1.5.0 */
 
 /* config.h is created by and PNG_CONFIGURE_LIBPNG is set by the "configure"
- * script.
+ * script.  We may need it here to get the correct configuration on things
+ * like limits.
  */
 #ifdef PNG_CONFIGURE_LIBPNG
 #  ifdef HAVE_CONFIG_H
@@ -43,6 +49,85 @@
 #  endif
 #endif
 
+/* Moved to pngpriv.h at libpng-1.5.0 */
+/* If you are running on a machine where you cannot allocate more
+ * than 64K of memory at once, uncomment this.  While libpng will not
+ * normally need that much memory in a chunk (unless you load up a very
+ * large file), zlib needs to know how big of a chunk it can use, and
+ * libpng thus makes sure to check any memory allocation to verify it
+ * will fit into memory.
+ *
+ * zlib provides 'MAXSEG_64K' which, if defined, indicates the
+ * same limit and pngconf.h (already included) sets the limit
+ * if certain operating systems are detected.
+ */
+#if defined(MAXSEG_64K) && !defined(PNG_MAX_MALLOC_64K)
+#  define PNG_MAX_MALLOC_64K
+#endif
+
+/* Moved to pngpriv.h at libpng-1.5.0 */
+/* Feature support: in 1.4 this was in pngconf.h, but these
+ * features have no affect on the libpng API.  Add library
+ * only features to the end of this list.  Add features that
+ * affect the API to scipts/config.dfn using png_on or png_off
+ * as determined by the default and update scripts/config.std
+ */
+/* Added at libpng version 1.4.0 */
+#if !defined(PNG_NO_WARNINGS) && !defined(PNG_WARNINGS_SUPPORTED)
+#  define PNG_WARNINGS_SUPPORTED
+#endif
+
+/* Added at libpng version 1.4.0 */
+#if !defined(PNG_NO_CHECK_cHRM) && !defined(PNG_CHECK_cHRM_SUPPORTED)
+#  define PNG_CHECK_cHRM_SUPPORTED
+#endif
+
+/* Added at libpng version 1.4.0 */
+#if !defined(PNG_NO_ALIGNED_MEMORY) && !defined(PNG_ALIGNED_MEMORY_SUPPORTED)
+#  define PNG_ALIGNED_MEMORY_SUPPORTED
+#endif
+
+/* Buggy compilers (e.g., gcc 2.7.2.2) need PNG_NO_POINTER_INDEXING
+ * See png[wr]util.c
+ */
+#if !defined(PNG_NO_POINTER_INDEXING) && \
+    !defined(PNG_POINTER_INDEXING_SUPPORTED)
+#  define PNG_POINTER_INDEXING_SUPPORTED
+#endif
+
+/* Other defines for things like memory and the like can go here.  */
+
+/* This controls how fine the dithering gets.  As this allocates
+ * a largish chunk of memory (32K), those who are not as concerned
+ * with dithering quality can decrease some or all of these.
+ */
+#ifndef PNG_DITHER_RED_BITS
+#  define PNG_DITHER_RED_BITS 5
+#endif
+#ifndef PNG_DITHER_GREEN_BITS
+#  define PNG_DITHER_GREEN_BITS 5
+#endif
+#ifndef PNG_DITHER_BLUE_BITS
+#  define PNG_DITHER_BLUE_BITS 5
+#endif
+
+/* This controls how fine the gamma correction becomes when you
+ * are only interested in 8 bits anyway.  Increasing this value
+ * results in more memory being used, and more pow() functions
+ * being called to fill in the gamma tables.  Don't set this value
+ * less then 8, and even that may not work (I haven't tested it).
+ */
+#ifndef PNG_MAX_GAMMA_8
+#  define PNG_MAX_GAMMA_8 11
+#endif
+
+/* This controls how much a difference in gamma we can tolerate before
+ * we actually start doing gamma conversion.
+ */
+#ifndef PNG_GAMMA_THRESHOLD
+#  define PNG_GAMMA_THRESHOLD 0.05
+#endif
+
 /* The functions exported by PNG_EXTERN are internal functions, which
  * aren't usually used outside the library (as far as I know), so it is
  * debatable if they should be exported at all.  In the future, when it
@@ -92,6 +177,31 @@
 #  endif
 #endif
 
+/* This is the size of the compression buffer, and thus the size of
+ * an IDAT chunk.  Make this whatever size you feel is best for your
+ * machine.  One of these will be allocated per png_struct.  When this
+ * is full, it writes the data to the disk, and does some other
+ * calculations.  Making this an extremely small size will slow
+ * the library down, but you may want to experiment to determine
+ * where it becomes significant, if you are concerned with memory
+ * usage.  Note that zlib allocates at least 32Kb also.  For readers,
+ * this describes the size of the buffer available to read the data in.
+ * Unless this gets smaller than the size of a row (compressed),
+ * it should not make much difference how big this is.
+ */
+
+#ifndef PNG_ZBUF_SIZE
+#  define PNG_ZBUF_SIZE 8192
+#endif
+
+/* Just a little check that someone hasn't tried to define something
+ * contradictory.
+ */
+#if (PNG_ZBUF_SIZE > 65536L) && defined(PNG_MAX_MALLOC_64K)
+#  undef PNG_ZBUF_SIZE
+#  define PNG_ZBUF_SIZE 65536L
+#endif
+
 /* Various modes of operation.  Note that after an init, mode is set to
  * zero automatically when the structure is created.
  */