more docs work
This commit is contained in:
John Cupitt
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@ -15,7 +15,7 @@
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<refpurpose>How to write bindings for libvips</refpurpose>
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</refnamediv>
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<refsect1 id="binding-goi">
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<refsect3 id="binding-goi">
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<title>Binding and gobject-introspection</title>
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<para>
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The C source code
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@ -89,6 +89,6 @@ $ yelp-build html .
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</para>
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</refsect1>
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</refsect3>
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</refentry>
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@ -14,13 +14,29 @@
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<refpurpose>How to add operations to VIPS</refpurpose>
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</refnamediv>
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<refsect1 id="extending-pointtopoint">
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<title>A simple point-to-point operation</title>
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<refsect3 id="extending-intro">
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<title>Introduction</title>
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<para>
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This section runs quickly through adding a simple operator to VIPS.
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For more information, see #VipsOperation and #VipsRegion. A good
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starting point for a new operation is a similar one in the VIPS library.
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</para>
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<para>
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All operations are subclasses of #VipsOperation, which in turn
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subclasses #VipsObject and then %GObject. You need to define a new
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instance struct and a new class struct.
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All VIPS operations are subclasses of #VipsOperation, which in turn
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subclasses #VipsObject and then %GObject. You add an operation to VIPS
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by defining a new subclass of #VipsOperation and arranging for its
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<code>class_init()</code> to be called, perhaps by calling its get_type()
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function.
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</para>
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</refsect3>
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<refsect3 id="extending-classstruct">
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<title>The class and object structures</title>
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<para>
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First you need to define a new
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object struct and a new class struct.
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<programlisting language="C">
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typedef struct _Negative {
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@ -48,8 +64,8 @@ typedef struct _NegativeClass {
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8-bit image, optionally letting you specify the value which the pixels
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"pivot" about. It doesn't need any class members (ie. values common
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to all operations of this type), so the second struct is empty. See
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vips_invert() for a more complete version of this operation that's
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actually in the library.
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the source to vips_invert() for a more complete version of this
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operation that's actually in the library.
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</para>
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<para>
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@ -59,16 +75,19 @@ typedef struct _NegativeClass {
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G_DEFINE_TYPE( Negative, negative, VIPS_TYPE_OPERATION );
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</programlisting>
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This defines a function called negative_get_type(),
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G_DEFINE_TYPE() defines a function called negative_get_type(),
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which registers this new class and returns its %GType (a
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pointer-sized integer). negative_get_type() in turn needs two
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functions, negative_init(), to initialise a new instance, and
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negative_class_init(), to initialise a new class.
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</para>
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</refsect3>
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<refsect3 id="extending-init">
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<title>Class and object initialisation</title>
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<para>
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negative_init() is very simple, it just sets the default value for
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our optional class parameter.
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our optional parameter.
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<programlisting language="C">
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static void
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@ -81,7 +100,7 @@ negative_init( Negative *negative )
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<para>
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negative_class_init() is more complicated: it has to set various
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fields in various superclasses.
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fields in various superclasses and define the operation's parameters.
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<programlisting language="C">
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static void
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@ -133,8 +152,13 @@ negative_class_init( NegativeClass *class )
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</para>
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<para>
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Finally, it needs to set the arguments this class constructor
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takes. There are a set of handy macros for doing this. The first few
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Finally, it needs to define the arguments the constructor for this class
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takes. There are a set of handy macros for doing this, see
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VIPS_ARG_INT() and friends.
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</para>
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<para>
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The first few
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parameters are always the same and mean: class pointer for argument,
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argument name, argument priority (bindings expect required arguments in
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order of priority), long argument name (this one is internationalised
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@ -147,11 +171,15 @@ negative_class_init( NegativeClass *class )
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Integer arguments take three more values: the minimum, maximum and
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default value for the argument.
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</para>
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</refsect3>
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<refsect3 id="extending-build">
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<title>The build() function</title>
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<para>
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The build function is the thing #VipsObject calls after supplying
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arguments. It checks that all required arguments have been set and are
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valid and constructs the object. After build, the object is expected
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The build function is the thing #VipsObject calls during object
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construction, after all arguments have been supplied and before the
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object is used. It has two roles: to verify that arguments are correct,
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and then to construct the object. After build(), the object is expected
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to be ready for use.
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<programlisting language="C">
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@ -193,7 +221,8 @@ negative_build( VipsObject *object )
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<para>
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Next, it adds its own checks. This is a demo operation, so we just
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work for uncoded, unsigned 8-bit images.
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work for uncoded, unsigned 8-bit images. There are a lot of
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convenience functions like vips_check_format(), see the docs.
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</para>
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<para>
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@ -204,18 +233,35 @@ negative_build( VipsObject *object )
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<para>
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vips_image_pipelinev() links our new image onto the input image and
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notes that this operation prefers to work in lines.
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notes that this operation prefers to work in lines. You can request
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other input geometries, see #VipsDemandStyle.
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</para>
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<para>
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The geometry hint is just a hint, an operation needs to be able to
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supply any size
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#VipsRegion on request. If you must have a certain size request, you can
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put a cache in the pipeline after your operation, see vips_linecache()
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and vips_tilecache(). You can also make requests to your operation
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ordered, see vips_sequential().
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</para>
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<para>
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Finally, vips_image_generate() attaches a set of callbacks to the
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output image to generate chunks of it on request. vips_start_one()
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and vips_stop_one() are convenience functions that make the input
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region for you.
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region for you, see below.
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</para>
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</refsect3>
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<refsect3 id="extending-gen">
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<title>The generate() function</title>
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<para>
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And then the actual image processing.
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The generate() function does the actual image processing.
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negative_generate() (of type #VipsGenerateFn, supplied to
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vips_image_generate() above) is
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called whenever some pixels of our output image are required.
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<programlisting language="C">
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static int
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@ -230,6 +276,7 @@ negative_generate( VipsRegion *or,
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*/
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VipsRegion *ir = (VipsRegion *) vseq;
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VipsImage *in = (VipsImage *) a;
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Negative *negative = (Negative *) b;
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int line_size = r->width * negative->in->Bands;
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@ -258,14 +305,57 @@ negative_generate( VipsRegion *or,
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<para>
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This has to calculate a section of the output image. The output
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#VipsRegion, @or, contains a #VipsRect called @valid which is the
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area needing calculation. negative_generate() asks for the
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corresponding pixels from the input region, then loops over the
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area. VIPS_REGION_ADDR() is a simple macro that does pointer arithmetic
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for you: you need to stay within the valid area.
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area needing calculation. This call to negative_generate() must
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somehow make this part of @or contain pixel data.
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</para>
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<para>
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To add the operation to vips, just call negative_get_type(). You
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@vseq is the sequence value. This is the
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per-thread state for this generate, created (in this example) by
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vips_start_one(). In this simple case it's just a #VipsRegion defined on
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the input image. If you need more per-thread state you can write your
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own start and stop functions and have a struct you create and pass as a
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sequence value. There are plenty of examples in the VIPS source code,
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see vips_rank().
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</para>
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<para>
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@a and @b are the last two arguments to vips_image_generate() above.
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@stop is a bool pointer you can set to stop computation early. vips_min()
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on an unsigned int image, for example, will set @stop as soon as it sees
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a zero, and will not scan the entire image.
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</para>
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<para>
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The first thing negative_generate() does is
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use vips_region_prepare() to
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ask for the corresponding pixels from the input image. Operations which
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do coordinate transforms or which need an area of input for each output
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point will need to calculate a new rect before calling
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vips_region_prepare().
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</para>
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<para>
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Finally, it can calculate some pixels. negative_generate() loops
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over the valid area of the output and calls VIPS_REGION_ADDR() for each
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line. This macro is reasonaly quick, but it's best not to call it for
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each pixel. Once per line is fine though.
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</para>
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</refsect3>
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<refsect3 id="extending-add">
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<title>Adding to VIPS</title>
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<para>
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To add the operation to vips, just call negative_get_type(). You can
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include the source in your program, or use %GModule to make a binary
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plugin that will be loaded by libvips at startup. There are some <ulink
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role="online-location"
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url="https://github.com/jcupitt/vips-gmic">example
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plugins available</ulink>.
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</para>
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<para>
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You
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can then use @negative from any of the vips interfaces. For example,
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in Python you'd use it like this:
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@ -324,10 +414,9 @@ if( negative( in, &out, "image_max", 128, NULL ) )
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and it's at least a bit safer.
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</para>
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</refsect3>
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</refsect1>
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<refsect1 id="extending-othertypes">
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<refsect3 id="extending-othertypes">
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<title>Other types of operation</title>
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<para>
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Change the _build() function to make other types of operation.
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@ -368,6 +457,6 @@ if( negative( in, &out, "image_max", 128, NULL ) )
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Make zero-copy operations, like vips_insert(), with vips_region_region().
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</para>
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</refsect1>
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</refsect3>
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</refentry>
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@ -15,7 +15,7 @@
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<refpurpose>The VIPS file format</refpurpose>
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</refnamediv>
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<refsect1 id="vips-format">
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<refsect3 id="vips-format">
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<title>Introduction</title>
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<para>
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VIPS has a simple, native file format. It's very fast, there is no image
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@ -50,9 +50,9 @@ $ vips gamma t.v output.tif
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Finally, after the pixel data comes an optional block of XML containing
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any extra metadata, such as an ICC profile or the EXIF data.
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</para>
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</refsect1>
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</refsect3>
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<refsect1 id="vips-format-header">
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<refsect3 id="vips-format-header">
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<title>The header</title>
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<para>
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The fields in the VIPS header are always stored least-significant byte
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@ -186,9 +186,9 @@ $ vips gamma t.v output.tif
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</table>
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</para>
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</refsect1>
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</refsect3>
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<refsect1 id="vips-format-data">
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<refsect3 id="vips-format-data">
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<title>The image data</title>
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<para>
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If <code>coding</code> is set to #VIPS_CODING_NONE, pixels are stored in
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@ -223,9 +223,9 @@ $ vips gamma t.v output.tif
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section.
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</para>
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</refsect1>
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</refsect3>
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<refsect1 id="vips-format-metadata">
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<refsect3 id="vips-format-metadata">
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<title>The metadata</title>
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<para>
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Following the image data is a chunk of XML holding a simple list of
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@ -240,6 +240,6 @@ $ vips gamma t.v output.tif
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replace the XML.
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</para>
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</refsect1>
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</refsect3>
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</refentry>
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@ -15,7 +15,7 @@
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<refpurpose>List of VIPS functions and operators</refpurpose>
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</refnamediv>
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<refsect1 id="function-list">
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<refsect3 id="function-list">
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<title>Function list</title>
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<para>
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VIPS has a set of operators, each of which computes some useful image
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@ -1103,6 +1103,6 @@
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</table>
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</para>
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</refsect1>
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</refsect3>
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</refentry>
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@ -15,7 +15,7 @@
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<refpurpose>How to use the VIPS library from C</refpurpose>
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</refnamediv>
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<refsect1 id="using-C-intro">
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<refsect3 id="using-C-intro">
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<title>Introduction</title>
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<para>
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VIPS comes with a convenient, high-level C API. You should read the API
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@ -23,9 +23,9 @@
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overview. The <command>vips</command> program is handy for getting a
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summary of an operation's parameters.
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</para>
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</refsect1>
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</refsect3>
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<refsect1 id="using-C-startup">
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<refsect3 id="using-C-startup">
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<title>Library startup</title>
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<para>
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When your program starts, use VIPS_INIT()
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@ -40,9 +40,9 @@
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You can add the VIPS flags to your %GObject command-line processing
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with vips_add_option_entries(), see below.
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</para>
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</refsect1>
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</refsect3>
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<refsect1 id="using-C-vipsimage">
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<refsect3 id="using-C-vipsimage">
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<title>The #VipsImage class</title>
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<para>
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The basic data object is the #VipsImage. You can create an
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@ -62,9 +62,9 @@
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See <link linkend="libvips-header">VIPS Header</link> to read about
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image properties.
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</para>
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</refsect1>
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</refsect3>
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<refsect1 id="using-C-ref">
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<refsect3 id="using-C-ref">
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<title>Reference counting</title>
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<para>
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VIPS is based on the %GObject library and is therefore reference counted.
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@ -80,9 +80,9 @@
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See #VipsOperation for more detail on VIPS
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reference counting conventions.
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</para>
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</refsect1>
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</refsect3>
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<refsect1 id="using-C-operations">
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<refsect3 id="using-C-operations">
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<title>VIPS operations</title>
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<para>
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Use things like vips_invert() to manipulate your images. See
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@ -92,9 +92,9 @@
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the final image to a disc file, to a formatted memory buffer, or to
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C-style memory array. See vips_image_write_to_file() and friends.
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</para>
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</refsect1>
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</refsect3>
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<refsect1 id="using-C-pixels">
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<refsect3 id="using-C-pixels">
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<title>Getting pixels</title>
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<para>
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Use #VipsRegion to read pixels out of images. You can use
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@ -102,9 +102,9 @@
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memory to work. See <link linkend="extending">extending</link>
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for an introduction to writing your own operations.
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</para>
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</refsect1>
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</refsect3>
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<refsect1 id="using-C-errors">
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<refsect3 id="using-C-errors">
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<title>Error handling</title>
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<para>
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@ -112,9 +112,9 @@
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linkend="libvips-error">VIPS Error</link> to find out how to get and
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clear the error log.
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</para>
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</refsect1>
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</refsect3>
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<refsect1 id="using-C-example">
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<refsect3 id="using-C-example">
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<title>Example</title>
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<example>
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@ -184,6 +184,6 @@ main( int argc, char **argv )
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</programlisting>
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</example>
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</refsect1>
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</refsect3>
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</refentry>
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|
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|
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@ -15,7 +15,7 @@
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<refpurpose>How to use the VIPS library from the command-line</refpurpose>
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</refnamediv>
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<refsect1 id="using-command-line-intro">
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<refsect3 id="using-command-line-intro">
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<title>Introduction</title>
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<para>
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Use the <command>vips</command> command to execute VIPS operations from
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|
|
@ -46,9 +46,9 @@ where:
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There's a straightforward relationship with the C API: compare this to
|
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the API docs for vips_rot(), for example.
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</para>
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</refsect1>
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</refsect3>
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<refsect1 id="using-command-line-list">
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<refsect3 id="using-command-line-list">
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<title>Listing all operations</title>
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<para>
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You can list all classes with:
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|
|
@ -71,9 +71,9 @@ VipsOperation (operation), operations
|
|||
<literal>VipsForeign</literal> will show some of the extra flags
|
||||
supported by the file load/save operations.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="using-command-line-options">
|
||||
<refsect3 id="using-command-line-options">
|
||||
<title>Optional arguments</title>
|
||||
<para>
|
||||
Many operations take optional arguments. You can supply these as
|
||||
|
|
@ -109,9 +109,9 @@ $ vips gamma k2.jpg x.jpg --exponent 0.42
|
|||
This will read file <literal>k2.jpg</literal>, un-gamma it, and
|
||||
write the result to file <literal>x.jpg</literal>.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="using-command-line-array">
|
||||
<refsect3 id="using-command-line-array">
|
||||
<title>Array arguments</title>
|
||||
<para>
|
||||
Some operations take arrays of values as arguments, for example,
|
||||
|
|
@ -131,9 +131,9 @@ $ vips affine k2.jpg x.jpg "2 0 0 1"
|
|||
$ vips bandjoin "k2.jpg k4.jpg" x.tif
|
||||
</programlisting>
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="using-command-line-conversion">
|
||||
<refsect3 id="using-command-line-conversion">
|
||||
<title>Implicit file format conversion</title>
|
||||
<para>
|
||||
<command>vips</command> will automatically convert between image file
|
||||
|
|
@ -163,9 +163,9 @@ vips affine k2.jpg x.jpg[Q=90,strip] "2 0 0 1"
|
|||
Will write <literal>x.jpg</literal> at quality level 90 and will
|
||||
strip all metadata from the image.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="using-command-line-other">
|
||||
<refsect3 id="using-command-line-other">
|
||||
<title>Other features</title>
|
||||
|
||||
<para>
|
||||
|
|
@ -195,6 +195,6 @@ vips affine k2.jpg x.jpg[Q=90,strip] "2 0 0 1"
|
|||
images. <command>vipsthumbnail</command> can make image thumbnails
|
||||
quickly.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
</refentry>
|
||||
|
|
|
|||
|
|
@ -15,7 +15,7 @@
|
|||
<refpurpose>How to use the VIPS library from C++</refpurpose>
|
||||
</refnamediv>
|
||||
|
||||
<refsect1 id="using-cpp">
|
||||
<refsect3 id="using-cpp">
|
||||
<title>Introduction</title>
|
||||
<para>
|
||||
VIPS comes with a convenient C++ API. It is a very thin wrapper over the
|
||||
|
|
@ -219,9 +219,9 @@ VImage VImage::add( VImage right, VOption *options = 0 );
|
|||
you can write to a memory array, to a formatted image in memory, or to
|
||||
another image.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="cpp-expansion">
|
||||
<refsect3 id="cpp-expansion">
|
||||
<title>Automatic constant expansion</title>
|
||||
|
||||
<para>
|
||||
|
|
@ -256,9 +256,9 @@ VImage a = (a < 128).ifthenelse( 128, a );
|
|||
The C++ API includes the usual range of arithmetic operator overloads.
|
||||
You can mix constants, vectors and images freely.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="cpp-enum">
|
||||
<refsect3 id="cpp-enum">
|
||||
<title>Enum expansion</title>
|
||||
|
||||
<para>
|
||||
|
|
@ -284,9 +284,9 @@ VImage VImage::sin( VOption *options = 0 );
|
|||
</programlisting>
|
||||
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="cpp-extend">
|
||||
<refsect3 id="cpp-extend">
|
||||
<title>Extending the C++ interface</title>
|
||||
|
||||
<para>
|
||||
|
|
@ -326,5 +326,5 @@ VImage VImage::add(VImage right, VOption *options)
|
|||
|
||||
Where VImage::call() is the generic call-a-vips8-operation function.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
</refentry>
|
||||
|
|
|
|||
|
|
@ -15,7 +15,7 @@
|
|||
<refpurpose>How to use the VIPS library from Python</refpurpose>
|
||||
</refnamediv>
|
||||
|
||||
<refsect1 id="python-intro">
|
||||
<refsect3 id="python-intro">
|
||||
<title>Introduction</title>
|
||||
<para>
|
||||
VIPS comes with a convenient, high-level Python API based
|
||||
|
|
@ -97,9 +97,9 @@ im = im.similarity(scale = 0.9, interpolate = Vips.Interpolate.new("bicubic"))
|
|||
string containing the formatted image, and <code>.write()</code> to
|
||||
write to another image.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="python-basics">
|
||||
<refsect3 id="python-basics">
|
||||
<title><code>pyvips8</code> basics</title>
|
||||
<para>
|
||||
The Python interface comes in two main parts. First, the C source code
|
||||
|
|
@ -126,9 +126,9 @@ from gi.repository import Vips
|
|||
seem more pythonesque, vips includes a set of overrides which form a
|
||||
layer over the bare functions created by gobject-introspection.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="python-wrapping">
|
||||
<refsect3 id="python-wrapping">
|
||||
<title>Automatic wrapping</title>
|
||||
<para>
|
||||
The overrides intercept member lookup
|
||||
|
|
@ -275,9 +275,9 @@ result_image = image1.bandjoin([image2, 255])
|
|||
|
||||
and so on.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="python-doc">
|
||||
<refsect3 id="python-doc">
|
||||
<title>Automatic docstrings</title>
|
||||
<para>
|
||||
Try <code>help(Vips)</code> for everything,
|
||||
|
|
@ -299,9 +299,9 @@ help(image.add)
|
|||
And you'll get a summary of the operator's behaviour and how the
|
||||
arguments are represented in Python. Use the C API docs for more detail.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="python-exceptions">
|
||||
<refsect3 id="python-exceptions">
|
||||
<title>Exceptions</title>
|
||||
<para>
|
||||
The wrapper spots errors from vips operations and raises the
|
||||
|
|
@ -309,9 +309,9 @@ help(image.add)
|
|||
usual way. The <code>.detail</code> member gives the detailed
|
||||
error message.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="python-modify">
|
||||
<refsect3 id="python-modify">
|
||||
<title>Draw operations</title>
|
||||
<para>
|
||||
Paint operations like <code>draw_circle</code> and <code>draw_line</code>
|
||||
|
|
@ -333,9 +333,9 @@ help(image.add)
|
|||
If you want to avoid the copies, you'll need to call drawing
|
||||
operations yourself.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="python-overloads">
|
||||
<refsect3 id="python-overloads">
|
||||
<title>Overloads</title>
|
||||
<para>
|
||||
The wrapper defines the usual set of arithmetic, boolean and
|
||||
|
|
@ -347,9 +347,9 @@ help(image.add)
|
|||
result_image = ((image * [1, 2, 3]).abs() < 128) | 4
|
||||
</programlisting>
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="python-expansions">
|
||||
<refsect3 id="python-expansions">
|
||||
<title>Expansions</title>
|
||||
<para>
|
||||
Some vips operators take an enum to select an action, for example
|
||||
|
|
@ -369,9 +369,9 @@ result_image = image.sin()
|
|||
|
||||
See <code>help(Vips.Image)</code> for a list.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="python-utility">
|
||||
<refsect3 id="python-utility">
|
||||
<title>Convenience functions</title>
|
||||
<para>
|
||||
The wrapper defines a few extra useful utility functions:
|
||||
|
|
@ -383,9 +383,9 @@ result_image = image.sin()
|
|||
<code>.median()</code>.
|
||||
Again, see <code>help(Vips.Image)</code> for a list.
|
||||
</para>
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
<refsect1 id="python-args">
|
||||
<refsect3 id="python-args">
|
||||
<title>Command-line option parsing</title>
|
||||
<para>
|
||||
GLib includes a command-line option parser, and Vips defines a set of
|
||||
|
|
@ -405,6 +405,6 @@ context.parse(sys.argv)
|
|||
</programlisting>
|
||||
</para>
|
||||
|
||||
</refsect1>
|
||||
</refsect3>
|
||||
|
||||
</refentry>
|
||||
|
|
|
|||
Loading…
Reference in New Issue