static float gradient(const SrcView& src, const point_t& point, Color channel) {
point_t pR, pL, pU, pD;
if (point.x == 0)
pL = point_t(0, 0);
else
pL = point_t(-1, 0);
if (point.y == 0)
pD = point_t(0, 0);
else
pD = point_t(0, -1);
auto xRight = src.xy_at(point + point_t(1, 0));
auto xLeft = src.xy_at(point + pL);
auto yUp = src.xy_at(point + point_t(0, 1));
auto yDown = src.xy_at(point + pD);
auto xx = fabs(get_color(*xRight, channel) - get_color(*xLeft, channel));
auto yy = fabs(get_color(*yUp, channel) - get_color(*yDown, channel));
return sqrt((powf(xx, 2) + powf(yy, 2)));
}
bool sample(bilinear_sampler, const SrcView& src, const point2<F>& p, DstP& result) {
typedef typename SrcView::value_type SrcP;
///modif
point2<std::ptrdiff_t> p0(ifloor(p)); // the closest integer coordinate top left from p
point2<F> frac(p.x-p0.x, p.y-p0.y);
if (p0.x < 0 || p0.y < 0 || p0.x>=src.width() || p0.y>=src.height()) return false;
pixel<F,devicen_layout_t<num_channels<SrcView>::value> > mp(0); // suboptimal
typename SrcView::xy_locator loc=src.xy_at(p0.x,p0.y);
if (p0.x+1<src.width()) {
if (p0.y+1<src.height()) {
// most common case - inside the image, not on the last row or column
detail::add_dst_mul_src<SrcP,F,pixel<F,devicen_layout_t<num_channels<SrcView>::value> > >()(*loc, (1-frac.x)*(1-frac.y),mp);
detail::add_dst_mul_src<SrcP,F,pixel<F,devicen_layout_t<num_channels<SrcView>::value> > >()(loc.x()[1], frac.x *(1-frac.y),mp);
++loc.y();
detail::add_dst_mul_src<SrcP,F,pixel<F,devicen_layout_t<num_channels<SrcView>::value> > >()(*loc, (1-frac.x)* frac.y ,mp);
detail::add_dst_mul_src<SrcP,F,pixel<F,devicen_layout_t<num_channels<SrcView>::value> > >()(loc.x()[1], frac.x * frac.y ,mp);
} else {
// on the last row, but not the bottom-right corner pixel
detail::add_dst_mul_src<SrcP,F,pixel<F,devicen_layout_t<num_channels<SrcView>::value> > >()(*loc, (1-frac.x),mp);
detail::add_dst_mul_src<SrcP,F,pixel<F,devicen_layout_t<num_channels<SrcView>::value> > >()(loc.x()[1], frac.x ,mp);
}
} else {
if (p0.y+1<src.height()) {
// on the last column, but not the bottom-right corner pixel
detail::add_dst_mul_src<SrcP,F,pixel<F,devicen_layout_t<num_channels<SrcView>::value> > >()(*loc, (1-frac.y),mp);
++loc.y();
detail::add_dst_mul_src<SrcP,F,pixel<F,devicen_layout_t<num_channels<SrcView>::value> > >()(*loc, frac.y ,mp);
} else {
// the bottom-right corner pixel
detail::add_dst_mul_src<SrcP,F,pixel<F,devicen_layout_t<num_channels<SrcView>::value> > >()(*loc,1,mp);
}
}
// Convert from floating point average value to the source type
SrcP src_result;
cast_pixel(mp,src_result);
color_convert(src_result, result);
return true;
}