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more docs work

This commit is contained in:
John Cupitt 2014-08-12 13:37:16 +01:00
parent ce428ffa94
commit 2f72a9925f
5 changed files with 367 additions and 18 deletions
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3
ChangeLog
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@ -1,3 +1,6 @@
12/8/14 started 7.40.5
- more doc fixes
25/7/14 started 7.40.5
- fix a race in im_maxpos_avg()
- limit n_thr on tiny images

7
TODO
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@ -1,12 +1,15 @@
- can we pick the vipsthumbnail int shrink factor more intelligently?
- did we include the exif patch in the latest windows build? check on laptop
we don't seem to have this fix in the repository!
- vips_object_unref_outputs() needs docs ... bindings will need it
- copy-paste blog post about writing vips8 operations into 'extending'
- vips_init() has a deprecation warning, bizarre
- check and fix up docs
index items should all be links

6
configure.ac
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@ -2,7 +2,7 @@
# also update the version number in the m4 macros below
AC_INIT([vips], [7.40.5], [vipsip@jiscmail.ac.uk])
AC_INIT([vips], [7.40.6], [vipsip@jiscmail.ac.uk])
# required for gobject-introspection
AC_PREREQ(2.62)
@ -18,7 +18,7 @@ AC_CONFIG_MACRO_DIR([m4])
# user-visible library versioning
m4_define([vips_major_version], [7])
m4_define([vips_minor_version], [40])
m4_define([vips_micro_version], [5])
m4_define([vips_micro_version], [6])
m4_define([vips_version],
[vips_major_version.vips_minor_version.vips_micro_version])
@ -38,7 +38,7 @@ VIPS_VERSION_STRING=$VIPS_VERSION-`date`
# binary interface changes not backwards compatible?: reset age to 0
LIBRARY_CURRENT=38
LIBRARY_REVISION=3
LIBRARY_REVISION=4
LIBRARY_AGE=0
# patched into include/vips/version.h

12
doc/reference/binding.xml
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@ -19,6 +19,18 @@
<para>
Write this section once the vips8 Python binding is done.
</para>
<para>
If you are writing a language binding, you won't need these. Instead, make
a new operation with vips_operation_new() (all it does is look up the
operation by name with vips_type_find(), then call g_object_new() for you),
then use vips_argument_map() and friends to loop over the operation's
arguments setting them. Once you have set all arguments, use
vips_cache_operation_build() to look up the operation in the cache and
either build or dup it. If something goes wrong, you'll need to use
vips_object_unref_outputs() and g_object_unref() to free the
partially-built object.
</para>
</refsect1>
</refentry>

357
doc/reference/extending.xml
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@ -14,23 +14,354 @@
<refpurpose>How to add operations to VIPS</refpurpose>
</refnamediv>
<refsect1 id="extending-subclassing">
<title>Adding operations to VIPS</title>
<refsect1 id="extending-pointtopoint">
<title>A simple point-to-point operation</title>
<para>
All about subclassing. Copy-paste from the blog post about extending
vips8.
All operations are subclasses of #VipsOperation, which in turn
subclasses #VipsObject and then %GObject. You need to define a new
instance struct and a new class struct.
<programlisting language="C">
typedef struct _Negative {
VipsOperation parent_instance;
VipsImage *in;
VipsImage *out;
int image_max;
} Negative;
typedef struct _NegativeClass {
VipsOperationClass parent_class;
/* No new class members needed for this op.
*/
} NegativeClass;
</programlisting>
</para>
<para>
If you are writing a language binding, you won't need these. Instead, make
a new operation with vips_operation_new() (all it does is look up the
operation by name with vips_type_find(), then call g_object_new() for you),
then use vips_argument_map() and friends to loop over the operation's
arguments setting them. Once you have set all arguments, use
vips_cache_operation_build() to look up the operation in the cache and
either build or dup it. If something goes wrong, you'll need to use
vips_object_unref_outputs() and g_object_unref() to free the
partially-built object.
This operation will find the photographic negative of an unsigned
8-bit image, optionally letting you specify the value which the pixels
"pivot" about. It doesn't need any class members (ie. values common
to all operations of this type), so the second struct is empty. See
vips_invert() for a more complete version of this operation that's
actually in the library.
</para>
<para>
GObject has a handy macro to write some of the boilerplate for you.
<programlisting language="C">
G_DEFINE_TYPE( Negative, negative, VIPS_TYPE_OPERATION );
</programlisting>
This defines a function called negative_get_type(),
which registers this new class and returns its #GType (a
pointer-sized integer). negative_get_type() in turn needs two
functions, negative_init(), to initialise a new instance, and
negative_class_init(), to initialise a new class.
</para>
<para>
negative_init() is very simple, it just sets the default value for
our optional class parameter.
<programlisting language="C">
static void
negative_init( Negative *negative )
{
negative->image_max = 255;
}
</programlisting>
</para>
<para>
negative_class_init() is more complicated: it has to set various
fields in various superclasses.
<programlisting language="C">
static void
negative_class_init( NegativeClass *class )
{
GObjectClass *gobject_class = G_OBJECT_CLASS( class );
VipsObjectClass *object_class = VIPS_OBJECT_CLASS( class );
gobject_class->set_property = vips_object_set_property;
gobject_class->get_property = vips_object_get_property;
object_class->nickname = "negative";
object_class->description = "photographic negative";
object_class->build = negative_build;
VIPS_ARG_IMAGE( class, "in", 1,
"Input",
"Input image",
VIPS_ARGUMENT_REQUIRED_INPUT,
G_STRUCT_OFFSET( Negative, in ) );
VIPS_ARG_IMAGE( class, "out", 2,
"Output",
"Output image",
VIPS_ARGUMENT_REQUIRED_OUTPUT,
G_STRUCT_OFFSET( Negative, out ) );
VIPS_ARG_INT( class, "image_max", 4,
"Image maximum",
"Maximum value in image: pivot about this",
VIPS_ARGUMENT_OPTIONAL_INPUT,
G_STRUCT_OFFSET( Negative, image_max ),
0, 255, 255 );
}
</programlisting>
</para>
<para>
In %GObject, it needs to set the getters and setters for this class. vips
has a generic get/set system, so any subclass of #VipsObject needs to
use the vips ones.
</para>
<para>
In #VipsObject, it needs to set the operation @nickname and @description,
and set a build function (see below). @nickname is used to refer to
this operation in the API, @description is used to explain this
operation to users and will be translated into their language.
</para>
<para>
Finally, it needs to set the arguments this class constructor
takes. There are a set of handy macros for doing this. The first few
parameters are always the same and mean: class pointer for argument,
argument name, argument priority (bindings expect required arguments in
order of priority), long argument name (this one is internationalised
and displayed to users), description (again, users can see this),
some flags describing the argument, and finally the position of the
member in the struct.
</para>
<para>
Integer arguments take three more values: the minimum, maximum and
default value for the argument.
</para>
<para>
The build function is the thing VipsObject calls after supplying
arguments. It checks that all required arguments have been set and are
valid and constructs the object. After build, the object is expected
to be ready for use.
<programlisting language="C">
static int
negative_build( VipsObject *object )
{
VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( object );
Negative *negative = (Negative *) object;
if( VIPS_OBJECT_CLASS( negative_parent_class )->build( object ) )
return( -1 );
if( vips_check_uncoded( class->nickname, negative->in ) ||
vips_check_format( class->nickname, negative->in, VIPS_FORMAT_UCHAR ) )
return( -1 );
g_object_set( object, "out", vips_image_new(), NULL );
if( vips_image_pipelinev( negative->out,
VIPS_DEMAND_STYLE_THINSTRIP, negative->in, NULL ) )
return( -1 );
if( vips_image_generate( negative->out,
vips_start_one,
negative_generate,
vips_stop_one,
negative->in, negative ) )
return( -1 );
return( 0 );
}
</programlisting>
</para>
<para>
negative_build() first chains up to the superclass: this will check
that all input arguments have been supplied and are sane.
</para>
<para>
Next, it adds its own checks. This is a demo operation, so we just
work for uncoded, unsigned 8-bit images.
</para>
<para>
Next, it creates the output image. This needs to be set with
g_object_set() so that vips can see that it has been assigned. vips
will also handle the reference counting for you.
</para>
<para>
vips_image_pipelinev() links our new image onto the input image and
notes that this operation prefers to work in lines.
</para>
<para>
Finally, vips_image_generate() attaches a set of callbacks to the
output image to generate chunks of it on request. vips_start_one()
and vips_stop_one() are convenience functions that make the input
region for you.
</para>
<para>
And then the actual image processing.
<programlisting language="C">
static int
negative_generate( VipsRegion *or,
void *vseq, void *a, void *b, gboolean *stop )
{
/* The area of the output region we have been asked to make.
*/
VipsRect *r = &amp;or-&gt;valid;
/* The sequence value ... the thing returned by vips_start_one().
*/
VipsRegion *ir = (VipsRegion *) vseq;
Negative *negative = (Negative *) b;
int line_size = r-&gt;width * negative-&gt;in-&gt;Bands;
int x, y;
/* Request matching part of input region.
*/
if( vips_region_prepare( ir, r ) )
return( -1 );
for( y = 0; y &lt; r-&gt;height; y++ ) {
unsigned char *p = (unsigned char *)
VIPS_REGION_ADDR( ir, r-&gt;left, r-&gt;top + y );
unsigned char *q = (unsigned char *)
VIPS_REGION_ADDR( or, r-&gt;left, r-&gt;top + y );
for( x = 0; x &lt; line_size; x++ )
q[x] = negative-&gt;image_max - p[x];
}
return( 0 );
}
</programlisting>
</para>
<para>
This has to calculate a section of the output image. The output
#VipsRegion, @or, contains a #VipsRect called @valid which is the
area needing calculation. negative_generate() asks for the
corresponding pixels from the input region, then loops over the
area. VIPS_REGION_ADDR() is a simple macro that does pointer arithmetic
for you: you need to stay within the valid area.
</para>
<para>
To add the operation to vips, just call negative_get_type(). You
can then use @negative from any of the vips interfaces. For example,
in Python you'd use it like this:
<programlisting language="python">
out = in.negative(image_max = 128)
</programlisting>
</para>
<para>
From the command-line it'd look like this:
<programlisting language="bash">
$ vips negative in.png out.tif --image-max 128
</programlisting>
</para>
<para>
And from C like this:
<programlisting language="C">
VipsImage *in;
VipsImage *out;
if( vips_call( "negative", in, &amp;out, "image_max", 128, NULL ) )
... error
</programlisting>
</para>
<para>
Unfortunately that will do almost no compile-time type checking,
so all vips operations have a tiny extra wrapper to add a bit of
safety. For example:
<programlisting language="C">
static int
negative( VipsImage *in, VipsImage **out, ... )
{
va_list ap;
int result;
va_start( ap, out );
result = vips_call_split( "negative", ap, in, out );
va_end( ap );
return( result );
}
</programlisting>
</para>
<para>
And now you can write:
<programlisting language="C">
if( negative( in, &amp;out, "image_max", 128, NULL ) )
... error
</programlisting>
and it's at least a bit safer.
</para>
</refsect1>
<refsect1 id="extending-othertypes">
<title>Other types of operation</title>
<para>
Change the _build() function to make other types of operation.
</para>
<para>
Use vips_image_generate() with vips_start_many() to make operations
which demand pixels from more than one image at once, such as image
plus image.
</para>
<para>
Use vips_sink() instead of vips_image_generate() to loop over an image
and calculate a value. vips uses this for the statistics operations,
like vips_avg().
</para>
<para>
Use vips_image_wio_input() to get an entire image into memory so you
can read it with a pointer. This will obviously not scale well to
very large images, but some operations, like FFTs or flood-fill, need
the whole image to be available at once.
</para>
<para>
Make area operations, like filters, by enlarging the #VipsRect that
_generate() is given before calling vips_image_prepare(). You can
enlarge the input image, so that the output image is the same size as
the original input, by using vips_embed() within the _build() function.
</para>
<para>
Make things like flips and rotates by making larger changes to the
#VipsRect in _generate().
</para>
</refsect1>