boost::gil::pixel_2d_locator_base
base class for models of PixelLocatorConcept
Synopsis
Declared in <boost/gil/locator.hpp>
template<
typename Loc,
typename XIterator,
typename YIterator>
class pixel_2d_locator_base;Description
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);
locator+=offset2;
locator[offset2]=my_pixel;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 type aliases 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
using const_t = ...; // read-only locator
template <typename Deref> struct add_deref {
using type = ...; // locator that invokes the Deref dereference object upon pixel access
static type make(const my_locator& loc, const Deref& d);
};
my_locator();
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.
Derived Classes
Name |
Description |
Memory‐based pixel locator. Models: PixelLocatorConcept,HasDynamicXStepTypeConcept,HasDynamicYStepTypeConcept,HasTransposedTypeConcept |
|
A 2D locator over a virtual image Upon dereferencing, invokes a given function object passing it its coordinates. Models: PixelLocatorConcept, HasDynamicXStepTypeConcept, HasDynamicYStepTypeConcept, HasTransposedTypeConcept |
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