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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
- better fitting of fonts with overhanging edges, thanks Adrià
- lower stack use in radsave to help musl [Jacob Thrane Lund]
- better fitting of fonts with overhanging edges [Adrià]
- revise C++ example [fangqiao]
12/2/18 started 8.6.3
- use pkg-config to find libjpeg, if we can

83
doc/using-cpp.xml
View File

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