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pixel_2d_locator_base< Loc, XIterator, YIterator > Class Template Reference

base class for models of PixelLocatorConceptPixel locator is similar to a pixel iterator, but allows for 2D navigation of pixels within an image view. It has a 2D difference_type and supports random access operations like: More...

#include <locator.hpp>

Public Types

typedef XIterator x_iterator
typedef YIterator y_iterator
typedef std::iterator_traits
< x_iterator >::value_type 
typedef std::iterator_traits
< x_iterator >::reference 
typedef std::iterator_traits
< x_iterator >
typedef point2< coord_t > difference_type
typedef difference_type point_t
typedef point_t::template axis
< 0 >::coord_t 
typedef point_t::template axis
< 1 >::coord_t 
typedef difference_type cached_location_t

Public Member Functions

bool operator!= (const Loc &p) const
x_iterator x_at (x_coord_t dx, y_coord_t dy) const
x_iterator x_at (const difference_type &d) const
y_iterator y_at (x_coord_t dx, y_coord_t dy) const
y_iterator y_at (const difference_type &d) const
Loc xy_at (x_coord_t dx, y_coord_t dy) const
Loc xy_at (const difference_type &d) const
template<std::size_t D>
axis< D >::iterator & axis_iterator ()
template<std::size_t D>
axis< D >::iterator const & axis_iterator () const
template<std::size_t D>
axis< D >::iterator axis_iterator (const point_t &p) const
reference operator() (x_coord_t dx, y_coord_t dy) const
reference operator[] (const difference_type &d) const
reference operator* () const
Loc & operator+= (const difference_type &d)
Loc & operator-= (const difference_type &d)
Loc operator+ (const difference_type &d) const
Loc operator- (const difference_type &d) const
cached_location_t cache_location (const difference_type &d) const
cached_location_t cache_location (x_coord_t dx, y_coord_t dy) const

Static Public Attributes

static const std::size_t num_dimensions =2


template<typename X >
class pixel_2d_locator

Detailed Description

template<typename Loc, typename XIterator, typename YIterator>
class boost::gil::pixel_2d_locator_base< Loc, XIterator, YIterator >

base class for models of PixelLocatorConcept

Pixel locator is similar to a pixel iterator, but allows for 2D navigation of pixels within an image view. It has a 2D difference_type and supports random access operations like:

difference_type offset2(2,3);

In addition, each coordinate acts as a random-access iterator that can be modified separately: "++locator.x()" or "locator.y()+=10" thereby moving the locator horizontally or vertically.

It is called a locator because it doesn't implement the complete interface of a random access iterator. For example, increment and decrement operations don't make sense (no way to specify dimension). Also 2D difference between two locators cannot be computed without knowledge of the X position within the image.

This base class provides most of the methods and typedefs needed to create a model of a locator. GIL provides two locator models as subclasses of pixel_2d_locator_base. A memory-based locator, memory_based_2d_locator and a virtual locator, virtual_2d_locator. The minimum functionality a subclass must provide is this:

class my_locator : public pixel_2d_locator_base<my_locator, ..., ...> { // supply the types for x-iterator and y-iterator
typedef ... const_t; // read-only locator
template <typename Deref> struct add_deref {
typedef ... type; // locator that invokes the Deref dereference object upon pixel access
static type make(const my_locator& loc, const Deref& d);
my_locator(const my_locator& pl);
// constructors with dynamic step in y (and x). Only valid for locators with dynamic steps
my_locator(const my_locator& loc, coord_t y_step);
my_locator(const my_locator& loc, coord_t x_step, coord_t y_step, bool transpose);
bool operator==(const my_locator& p) const;
// return _references_ to horizontal/vertical iterators. Advancing them moves this locator
x_iterator& x();
y_iterator& y();
x_iterator const& x() const;
y_iterator const& y() const;
// return the vertical distance to another locator. Some models need the horizontal distance to compute it
y_coord_t y_distance_to(const my_locator& loc2, x_coord_t xDiff) const;
// return true iff incrementing an x-iterator located at the last column will position it at the first
// column of the next row. Some models need the image width to determine that.
bool is_1d_traversable(x_coord_t width) const;

Models may choose to override some of the functions in the base class with more efficient versions.

The documentation for this class was generated from the following file: