Save work on libpng PNG loader (Issue #90)

configure

@@ -1,6 +1,6 @@
 #! /bin/sh
 # Guess values for system-dependent variables and create Makefiles.
-# Generated by GNU Autoconf 2.71 for pdfio 1.4.1.
+# Generated by GNU Autoconf 2.71 for pdfio 1.5.0.
 #
 # Report bugs to <https://github.com/michaelrsweet/pdfio/issues>.
 #
@@ -610,8 +610,8 @@ MAKEFLAGS=
 # Identity of this package.
 PACKAGE_NAME='pdfio'
 PACKAGE_TARNAME='pdfio'
-PACKAGE_VERSION='1.4.1'
-PACKAGE_STRING='pdfio 1.4.1'
+PACKAGE_VERSION='1.5.0'
+PACKAGE_STRING='pdfio 1.5.0'
 PACKAGE_BUGREPORT='https://github.com/michaelrsweet/pdfio/issues'
 PACKAGE_URL='https://www.msweet.org/pdfio'
 
@@ -653,6 +653,7 @@ WARNINGS
 CSFLAGS
 LIBPDFIO_STATIC
 LIBPDFIO
+PKGCONFIG_LIBPNG
 PKGCONFIG_REQUIRES
 PKGCONFIG_LIBS_PRIVATE
 PKGCONFIG_LIBS
@@ -729,6 +730,7 @@ SHELL'
 ac_subst_files=''
 ac_user_opts='
 enable_option_checking
+enable_libpng
 enable_static
 enable_shared
 enable_debug
@@ -1293,7 +1295,7 @@ if test "$ac_init_help" = "long"; then
   # Omit some internal or obsolete options to make the list less imposing.
   # This message is too long to be a string in the A/UX 3.1 sh.
   cat <<_ACEOF
-\`configure' configures pdfio 1.4.1 to adapt to many kinds of systems.
+\`configure' configures pdfio 1.5.0 to adapt to many kinds of systems.
 
 Usage: $0 [OPTION]... [VAR=VALUE]...
 
@@ -1359,7 +1361,7 @@ fi
 
 if test -n "$ac_init_help"; then
   case $ac_init_help in
-     short | recursive ) echo "Configuration of pdfio 1.4.1:";;
+     short | recursive ) echo "Configuration of pdfio 1.5.0:";;
    esac
   cat <<\_ACEOF
 
@@ -1367,6 +1369,8 @@ Optional Features:
   --disable-option-checking  ignore unrecognized --enable/--with options
   --disable-FEATURE       do not include FEATURE (same as --enable-FEATURE=no)
   --enable-FEATURE[=ARG]  include FEATURE [ARG=yes]
+  --enable-libpng         use libpng for pdfioFileCreateImageObjFromFile,
+                          default=auto
   --disable-static        do not install static library
   --enable-shared         install shared library
   --enable-debug          turn on debugging, default=no
@@ -1456,7 +1460,7 @@ fi
 test -n "$ac_init_help" && exit $ac_status
 if $ac_init_version; then
   cat <<\_ACEOF
-pdfio configure 1.4.1
+pdfio configure 1.5.0
 generated by GNU Autoconf 2.71
 
 Copyright (C) 2021 Free Software Foundation, Inc.
@@ -1612,7 +1616,7 @@ cat >config.log <<_ACEOF
 This file contains any messages produced by compilers while
 running configure, to aid debugging if configure makes a mistake.
 
-It was created by pdfio $as_me 1.4.1, which was
+It was created by pdfio $as_me 1.5.0, which was
 generated by GNU Autoconf 2.71.  Invocation command line was
 
   $ $0$ac_configure_args_raw
@@ -2368,9 +2372,9 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
 
-PDFIO_VERSION="1.4.1"
-PDFIO_VERSION_MAJOR="`echo 1.4.1 | awk -F. '{print $1}'`"
-PDFIO_VERSION_MINOR="`echo 1.4.1 | awk -F. '{printf("%d\n",$2);}'`"
+PDFIO_VERSION="1.5.0"
+PDFIO_VERSION_MAJOR="`echo 1.5.0 | awk -F. '{print $1}'`"
+PDFIO_VERSION_MINOR="`echo 1.5.0 | awk -F. '{printf("%d\n",$2);}'`"
 
 
 
@@ -4099,6 +4103,55 @@ fi
 fi
 
 
+# Check whether --enable-libpng was given.
+if test ${enable_libpng+y}
+then :
+  enableval=$enable_libpng;
+fi
+
+
+PKGCONFIG_LIBPNG=""
+
+
+if test "x$PKGCONFIG" != x -a x$enable_libpng != xno
+then :
+
+    { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for libpng-1.6.x" >&5
+printf %s "checking for libpng-1.6.x... " >&6; }
+    if $PKGCONFIG --exists libpng16
+then :
+
+	{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+printf "%s\n" "yes" >&6; };
+
+printf "%s\n" "#define HAVE_LIBPNG 1" >>confdefs.h
+
+	CPPFLAGS="$($PKGCONFIG --cflags libpng16) -DHAVE_LIBPNG=1 $CPPFLAGS"
+	LIBS="$($PKGCONFIG --libs libpng16) -lz $LIBS"
+	PKGCONFIG_LIBPNG="libpng >= 1.6,"
+	PKGCONFIG_LIBS_PRIVATE="$($PKGCONFIG --libs libpng16) $PKGCONFIG_LIBS_PRIVATE"
+
+else $as_nop
+
+	{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
+printf "%s\n" "no" >&6; };
+	if test x$enable_libpng = xyes
+then :
+
+	    as_fn_error $? "libpng-dev 1.6 or later required for --enable-libpng." "$LINENO" 5
+
+fi
+
+fi
+
+elif test x$enable_libpng = xyes
+then :
+
+    as_fn_error $? "libpng-dev 1.6 or later required for --enable-libpng." "$LINENO" 5
+
+fi
+
+
 # Check whether --enable-static was given.
 if test ${enable_static+y}
 then :
@@ -4935,7 +4988,7 @@ cat >>$CONFIG_STATUS <<\_ACEOF || ac_write_fail=1
 # report actual input values of CONFIG_FILES etc. instead of their
 # values after options handling.
 ac_log="
-This file was extended by pdfio $as_me 1.4.1, which was
+This file was extended by pdfio $as_me 1.5.0, which was
 generated by GNU Autoconf 2.71.  Invocation command line was
 
   CONFIG_FILES    = $CONFIG_FILES
@@ -4991,7 +5044,7 @@ ac_cs_config_escaped=`printf "%s\n" "$ac_cs_config" | sed "s/^ //; s/'/'\\\\\\\\
 cat >>$CONFIG_STATUS <<_ACEOF || ac_write_fail=1
 ac_cs_config='$ac_cs_config_escaped'
 ac_cs_version="\\
-pdfio config.status 1.4.1
+pdfio config.status 1.5.0
 configured by $0, generated by GNU Autoconf 2.71,
   with options \\"\$ac_cs_config\\"