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/* */
/* Copyright 1998-2002 by Ullrich Koethe */
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#ifndef VIGRA_INTERPOLATING_ACCESSOR_HXX
#define VIGRA_INTERPOLATING_ACCESSOR_HXX
#include "accessor.hxx"
#include "diff2d.hxx"
namespace vigra {
/** \addtogroup DataAccessors
*/
//@{
/********************************************************/
/* */
/* BilinearInterpolatingAccessor */
/* */
/********************************************************/
/** \brief Bilinear interpolation at non-integer positions.
This accessor allows an image be accessed at arbitrary non-integer
coordinates and performs an bi-linear interpolation to
obtain a pixel value.
It uses the given ACCESSOR (which is usually the
accessor originally associated with the iterator)
to access data.
<b>\#include</b> \<vigra/accessor.hxx\>
Namespace: vigra
<b> Required Interface:</b>
\code
ITERATOR iter;
ACCESSOR a;
VALUETYPE destvalue;
float s;
int x, y;
destvalue = s * a(iter, x, y) + s * a(iter, x, y);
\endcode
*/
template <class ACCESSOR, class VALUETYPE>
class BilinearInterpolatingAccessor
{
public:
/** the iterators' pixel type
*/
typedef VALUETYPE value_type;
/** init from given accessor
*/
BilinearInterpolatingAccessor(ACCESSOR a)
: a_(a)
{}
/** Interpolate the data item at a non-integer position.
Ensure that no outside pixels are accessed if
(x, y) is near the image border (as long as
0 <= x <= width-1, 0 <= y <= height-1).
*/
template <class ITERATOR>
value_type operator()(ITERATOR const & i, float x, float y) const
{
int ix = int(x);
int iy = int(y);
float dx = x - ix;
float dy = y - iy;
value_type ret;
// avoid dereferencing the iterator outside its range
if(dx == 0.0)
{
if(dy == 0.0)
{
ret = a_(i, Diff2D(ix, iy));
}
else
{
ret = detail::RequiresExplicitCast<value_type>::cast(
(1.0 - dy) * a_(i, Diff2D(ix, iy)) +
dy * a_(i, Diff2D(ix, iy + 1)));
}
}
else
{
if(dy == 0.0)
{
ret = detail::RequiresExplicitCast<value_type>::cast(
(1.0 - dx) * a_(i, Diff2D(ix, iy)) +
dx * a_(i, Diff2D(ix + 1, iy)));
}
else
{
ret = detail::RequiresExplicitCast<value_type>::cast(
(1.0 - dx) * (1.0 - dy) * a_(i, Diff2D(ix, iy)) +
dx * (1.0 - dy) * a_(i, Diff2D(ix + 1, iy)) +
(1.0 - dx) * dy * a_(i, Diff2D(ix, iy + 1)) +
dx * dy * a_(i, Diff2D(ix + 1, iy + 1)));
}
}
return ret;
}
/** Interpolate the data item at a non-integer position.
This function works as long as 0 <= x < width-1,
0 <= y < height-1. It is slightly faster than <TT>operator()</TT>.
*/
template <class ITERATOR>
value_type unchecked(ITERATOR const & i, float x, float y) const
{
int ix = int(x);
int iy = int(y);
float dx = x - ix;
float dy = y - iy;
return detail::RequiresExplicitCast<value_type>::cast(
(1.0 - dx) * (1.0 - dy) * a_(i, Diff2D(ix, iy)) +
dx * (1.0 - dy) * a_(i, Diff2D(ix + 1, iy)) +
(1.0 - dx) * dy * a_(i, Diff2D(ix, iy + 1)) +
dx * dy * a_(i, Diff2D(ix + 1, iy + 1)));
}
private:
ACCESSOR a_;
};
//@}
} // namespace vigra
#endif /* VIGRA_INTERPOLATING_ACCESSOR_HXX */
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