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update cpp example 

thanks fangqiao

see https://github.com/jcupitt/libvips/issues/932
This commit is contained in:
John Cupitt 2018-04-08 11:44:15 +01:00
parent 915226db21
commit f3842dcc4b
2 changed files with 35 additions and 52 deletions
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4
ChangeLog
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@ -1,6 +1,6 @@
12/3/18 started 8.6.4 12/3/18 started 8.6.4
- better fitting of fonts with overhanging edges, thanks Adrià - better fitting of fonts with overhanging edges [Adrià]
- lower stack use in radsave to help musl [Jacob Thrane Lund] - revise C++ example [fangqiao]
12/2/18 started 8.6.3 12/2/18 started 8.6.3
- use pkg-config to find libjpeg, if we can - use pkg-config to find libjpeg, if we can

83
doc/using-cpp.xml
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@ -26,7 +26,7 @@
<programlisting language="cpp"> <programlisting language="cpp">
/* compile with: /* compile with:
* g++ -g -Wall try.cc `pkg-config vips-cpp --cflags --libs` * g++ -g -Wall example.cc `pkg-config vips-cpp --cflags --libs`
*/ */
#include &lt;vips/vips8&gt; #include &lt;vips/vips8&gt;
@ -34,64 +34,47 @@
using namespace vips; using namespace vips;
int int
main( int argc, char **argv ) main (int argc, char **argv)
{ {
GOptionContext *context; if (VIPS_INIT (argv[0]))
GOptionGroup *main_group; vips_error_exit (NULL);
GError *error = NULL;
if (argc != 3)
vips_error_exit ("usage: %s input-file output-file", argv[0]);
if( VIPS_INIT( argv[0] ) ) VImage in = VImage::new_from_file (argv[1],
vips_error_exit( NULL ); VImage::option ()-&gt;set ("access", VIPS_ACCESS_SEQUENTIAL));
context = g_option_context_new( "" ); double avg = in.avg ();
main_group = g_option_group_new( NULL, NULL, NULL, NULL, NULL ); printf ("avg = %g\n", avg);
g_option_context_set_main_group( context, main_group ); printf ("width = %d\n", in.width ());
g_option_context_add_group( context, vips_get_option_group() );
in = VImage::new_from_file (argv[1],
if( !g_option_context_parse( context, &amp;argc, &amp;argv, &amp;error ) ) { VImage::option ()-&gt;set ("access", VIPS_ACCESS_SEQUENTIAL));
if( error ) {
fprintf( stderr, "%s\n", error->message ); VImage out = in.embed (10, 10, 1000, 1000,
g_error_free( error ); VImage::option ()-&gt;
} set ("extend", "background")-&gt;
set ("background", 128));
vips_error_exit( NULL );
} out.write_to_file (argv[2]);
VImage in = VImage::new_from_file( argv[1], vips_shutdown ();
VImage::option()->
set( "access", VIPS_ACCESS_SEQUENTIAL ) ); return (0);
double avg = in.avg();
printf( "avg = %g\n", avg );
printf( "width = %d\n", in.width() );
VImage in = VImage::new_from_file( argv[1],
VImage::option()->
set( "access", VIPS_ACCESS_SEQUENTIAL ) );
VImage out = in.embed( 10, 10, 1000, 1000,
VImage::option()->
set( "extend", "background" )->
set( "background", 128 ) );
out.write_to_file( argv[2] );
vips_shutdown();
return( 0 );
} }
</programlisting> </programlisting>
<para> <para>
Everything before <code>VImage in = VImage::..</code> is exactly Everything before <code>VImage in = VImage::..</code> is exactly
as the C API. This boilerplate gives the example a set of standard as the C API. vips_error_exit() just prints the arguments plus the
command-line flags. libvips error log and exits with an error code.
</para> </para>
<para> <para>
This line is the C++ equivalent of vips_image_new_from_file(). It works <code>VImage in = VImage::..</code> is the C++ equivalent of
vips_image_new_from_file(). It works
in the same way, the differences being: in the same way, the differences being:
<itemizedlist> <itemizedlist>