ceph/src/boost/boost/gil/color_base.hpp

   1 //
   2 // Copyright 2005-2007 Adobe Systems Incorporated
   3 // Copyright 2019 Mateusz Loskot <mateusz at loskot dot net>
   4 //
   5 // Distributed under the Boost Software License, Version 1.0
   6 // See accompanying file LICENSE_1_0.txt or copy at
   7 // http://www.boost.org/LICENSE_1_0.txt
   8 //
   9 #ifndef BOOST_GIL_COLOR_BASE_HPP
  10 #define BOOST_GIL_COLOR_BASE_HPP
  11
  12 #include <boost/gil/utilities.hpp>
  13 #include <boost/gil/concepts.hpp>
  14 #include <boost/gil/detail/mp11.hpp>
  15
  16 #include <boost/assert.hpp>
  17 #include <boost/config.hpp>
  18
  19 #include <type_traits>
  20
  21 namespace boost { namespace gil {
  22
  23 // Forward-declare
  24 template <typename P> P* memunit_advanced(const P* p, std::ptrdiff_t diff);
  25
  26 // Forward-declare semantic_at_c
  27 template <int K, typename ColorBase>
  28 auto semantic_at_c(ColorBase& p)
  29     -> typename std::enable_if
  30     <
  31         !std::is_const<ColorBase>::value,
  32         typename kth_semantic_element_reference_type<ColorBase, K>::type
  33     >::type;
  34
  35
  36 template <int K, typename ColorBase>
  37 typename kth_semantic_element_const_reference_type<ColorBase,K>::type semantic_at_c(const ColorBase& p);
  38
  39 // Forward declare element_reference_type
  40 template <typename ColorBase> struct element_reference_type;
  41 template <typename ColorBase> struct element_const_reference_type;
  42 template <typename ColorBase, int K> struct kth_element_type;
  43 template <typename ColorBase, int K> struct kth_element_type<const ColorBase,K> : public kth_element_type<ColorBase,K> {};
  44 template <typename ColorBase, int K> struct kth_element_reference_type;
  45 template <typename ColorBase, int K> struct kth_element_reference_type<const ColorBase,K> : public kth_element_reference_type<ColorBase,K> {};
  46 template <typename ColorBase, int K> struct kth_element_const_reference_type;
  47 template <typename ColorBase, int K> struct kth_element_const_reference_type<const ColorBase,K> : public kth_element_const_reference_type<ColorBase,K> {};
  48
  49 namespace detail {
  50
  51 template <typename DstLayout, typename SrcLayout, int K>
  52 struct mapping_transform : mp11::mp_at
  53     <
  54         typename SrcLayout::channel_mapping_t,
  55         typename detail::type_to_index
  56         <
  57             typename DstLayout::channel_mapping_t,
  58             std::integral_constant<int, K>
  59         >
  60     >::type
  61 {};
  62
  63 /// \defgroup ColorBaseModelHomogeneous detail::homogeneous_color_base
  64 /// \ingroup ColorBaseModel
  65 /// \brief A homogeneous color base holding one color element.
  66 /// Models HomogeneousColorBaseConcept or HomogeneousColorBaseValueConcept
  67 /// If the element type models Regular, this class models HomogeneousColorBaseValueConcept.
  68
  69 #if BOOST_WORKAROUND(BOOST_MSVC, >= 1400)
  70 #pragma warning(push)
  71 #pragma warning(disable:4512) //assignment operator could not be generated
  72 #endif
  73
  74 /// \brief A homogeneous color base holding one color element.
  75 /// Models HomogeneousColorBaseConcept or HomogeneousColorBaseValueConcept
  76 /// \ingroup ColorBaseModelHomogeneous
  77 template <typename Element, typename Layout>
  78 struct homogeneous_color_base<Element, Layout, 1>
  79 {
  80     using layout_t = Layout;
  81
  82     homogeneous_color_base() = default;
  83     homogeneous_color_base(Element v) : v0_(v) {}
  84
  85     template <typename E2, typename L2>
  86     homogeneous_color_base(homogeneous_color_base<E2, L2, 1> const& c)
  87         : v0_(gil::at_c<0>(c))
  88     {}
  89
  90     auto at(std::integral_constant<int, 0>)
  91         -> typename element_reference_type<homogeneous_color_base>::type
  92     { return v0_; }
  93
  94     auto at(std::integral_constant<int, 0>) const
  95         -> typename element_const_reference_type<homogeneous_color_base>::type
  96     { return v0_; }
  97
  98     // grayscale pixel values are convertible to channel type
  99     // FIXME: explicit?
 100     operator Element() const { return v0_; }
 101
 102 private:
 103     Element v0_{};
 104 };
 105
 106 /// \brief A homogeneous color base holding two color elements
 107 /// Models HomogeneousColorBaseConcept or HomogeneousColorBaseValueConcept
 108 /// \ingroup ColorBaseModelHomogeneous
 109 template <typename Element, typename Layout>
 110 struct homogeneous_color_base<Element, Layout, 2>
 111 {
 112     using layout_t = Layout;
 113
 114     homogeneous_color_base() = default;
 115     explicit homogeneous_color_base(Element v) : v0_(v), v1_(v) {}
 116     homogeneous_color_base(Element v0, Element v1) : v0_(v0), v1_(v1) {}
 117
 118     template <typename E2, typename L2>
 119     homogeneous_color_base(homogeneous_color_base<E2, L2, 2> const& c)
 120         : v0_(gil::at_c<mapping_transform<Layout, L2, 0>::value>(c))
 121         , v1_(gil::at_c<mapping_transform<Layout, L2, 1>::value>(c))
 122     {}
 123
 124     // Support for l-value reference proxy copy construction
 125     template <typename E2, typename L2>
 126     homogeneous_color_base(homogeneous_color_base<E2, L2, 2>& c)
 127         : v0_(gil::at_c<mapping_transform<Layout, L2, 0>::value>(c))
 128         , v1_(gil::at_c<mapping_transform<Layout, L2, 1>::value>(c))
 129     {}
 130
 131     // Support for planar_pixel_iterator construction and dereferencing
 132     template <typename P>
 133     homogeneous_color_base(P* p, bool)
 134         : v0_(&semantic_at_c<0>(*p))
 135         , v1_(&semantic_at_c<1>(*p))
 136     {}
 137
 138     // Support for planar_pixel_reference offset constructor
 139     template <typename Ptr>
 140     homogeneous_color_base(Ptr const& ptr, std::ptrdiff_t diff)
 141         : v0_(*memunit_advanced(semantic_at_c<0>(ptr), diff))
 142         , v1_(*memunit_advanced(semantic_at_c<1>(ptr), diff))
 143     {}
 144
 145     template <typename Ref>
 146     Ref deref() const
 147     {
 148         return Ref(*semantic_at_c<0>(*this), *semantic_at_c<1>(*this));
 149     }
 150
 151     auto at(std::integral_constant<int, 0>)
 152         -> typename element_reference_type<homogeneous_color_base>::type
 153     { return v0_; }
 154
 155     auto at(std::integral_constant<int, 0>) const
 156         -> typename element_const_reference_type<homogeneous_color_base>::type
 157     { return v0_; }
 158
 159     auto at(std::integral_constant<int, 1>)
 160         -> typename element_reference_type<homogeneous_color_base>::type
 161     { return v1_; }
 162
 163     auto at(std::integral_constant<int, 1>) const
 164         -> typename element_const_reference_type<homogeneous_color_base>::type
 165     { return v1_; }
 166
 167     // Support for planar_pixel_reference operator[]
 168     Element at_c_dynamic(std::size_t i) const
 169     {
 170         if (i == 0)
 171             return v0_;
 172         else
 173             return v1_;
 174     }
 175
 176 private:
 177     Element v0_{};
 178     Element v1_{};
 179 };
 180
 181 /// \brief A homogeneous color base holding three color elements.
 182 /// Models HomogeneousColorBaseConcept or HomogeneousColorBaseValueConcept
 183 /// \ingroup ColorBaseModelHomogeneous
 184 template <typename Element, typename Layout>
 185 struct homogeneous_color_base<Element, Layout, 3>
 186 {
 187     using layout_t = Layout;
 188
 189     homogeneous_color_base() = default;
 190     explicit homogeneous_color_base(Element v) : v0_(v), v1_(v), v2_(v) {}
 191     homogeneous_color_base(Element v0, Element v1, Element v2)
 192         : v0_(v0), v1_(v1), v2_(v2)
 193     {}
 194
 195     template <typename E2, typename L2>
 196     homogeneous_color_base(homogeneous_color_base<E2, L2, 3> const& c)
 197         : v0_(gil::at_c<mapping_transform<Layout, L2, 0>::value>(c))
 198         , v1_(gil::at_c<mapping_transform<Layout, L2, 1>::value>(c))
 199         , v2_(gil::at_c<mapping_transform<Layout, L2, 2>::value>(c))
 200     {}
 201
 202     // Support for l-value reference proxy copy construction
 203     template <typename E2, typename L2>
 204     homogeneous_color_base(homogeneous_color_base<E2, L2, 3>& c)
 205         : v0_(gil::at_c<mapping_transform<Layout, L2, 0>::value>(c))
 206         , v1_(gil::at_c<mapping_transform<Layout, L2, 1>::value>(c))
 207         , v2_(gil::at_c<mapping_transform<Layout, L2, 2>::value>(c))
 208     {}
 209
 210     // Support for planar_pixel_iterator construction and dereferencing
 211     template <typename P>
 212     homogeneous_color_base(P* p, bool)
 213         : v0_(&semantic_at_c<0>(*p))
 214         , v1_(&semantic_at_c<1>(*p))
 215         , v2_(&semantic_at_c<2>(*p))
 216     {}
 217
 218     // Support for planar_pixel_reference offset constructor
 219     template <typename Ptr>
 220     homogeneous_color_base(Ptr const& ptr, std::ptrdiff_t diff)
 221         : v0_(*memunit_advanced(semantic_at_c<0>(ptr), diff))
 222         , v1_(*memunit_advanced(semantic_at_c<1>(ptr), diff))
 223         , v2_(*memunit_advanced(semantic_at_c<2>(ptr), diff))
 224     {}
 225
 226     template <typename Ref>
 227     Ref deref() const
 228     {
 229         return Ref(
 230             *semantic_at_c<0>(*this),
 231             *semantic_at_c<1>(*this),
 232             *semantic_at_c<2>(*this));
 233     }
 234
 235     auto at(std::integral_constant<int, 0>)
 236         -> typename element_reference_type<homogeneous_color_base>::type
 237     { return v0_; }
 238
 239     auto at(std::integral_constant<int, 0>) const
 240         -> typename element_const_reference_type<homogeneous_color_base>::type
 241     { return v0_; }
 242
 243     auto at(std::integral_constant<int, 1>)
 244         -> typename element_reference_type<homogeneous_color_base>::type
 245     { return v1_; }
 246
 247     auto at(std::integral_constant<int, 1>) const
 248         -> typename element_const_reference_type<homogeneous_color_base>::type
 249     { return v1_; }
 250
 251     auto at(std::integral_constant<int, 2>)
 252         -> typename element_reference_type<homogeneous_color_base>::type
 253     { return v2_; }
 254
 255     auto at(std::integral_constant<int, 2>) const
 256         -> typename element_const_reference_type<homogeneous_color_base>::type
 257     { return v2_; }
 258
 259     // Support for planar_pixel_reference operator[]
 260     Element at_c_dynamic(std::size_t i) const
 261     {
 262         switch (i)
 263         {
 264         case 0: return v0_;
 265         case 1: return v1_;
 266         }
 267         return v2_;
 268     }
 269
 270 private:
 271     Element v0_{};
 272     Element v1_{};
 273     Element v2_{};
 274 };
 275
 276 /// \brief A homogeneous color base holding four color elements.
 277 /// Models HomogeneousColorBaseConcept or HomogeneousColorBaseValueConcept
 278 /// \ingroup ColorBaseModelHomogeneous
 279 template <typename Element, typename Layout>
 280 struct homogeneous_color_base<Element, Layout, 4>
 281 {
 282     using layout_t = Layout;
 283
 284     homogeneous_color_base() = default;
 285     explicit homogeneous_color_base(Element v) : v0_(v), v1_(v), v2_(v), v3_(v) {}
 286     homogeneous_color_base(Element v0, Element v1, Element v2, Element v3)
 287         : v0_(v0), v1_(v1), v2_(v2), v3_(v3)
 288     {}
 289
 290     template <typename E2, typename L2>
 291     homogeneous_color_base(homogeneous_color_base<E2, L2, 4> const& c)
 292         : v0_(gil::at_c<mapping_transform<Layout, L2, 0>::value>(c))
 293         , v1_(gil::at_c<mapping_transform<Layout, L2, 1>::value>(c))
 294         , v2_(gil::at_c<mapping_transform<Layout, L2, 2>::value>(c))
 295         , v3_(gil::at_c<mapping_transform<Layout, L2, 3>::value>(c))
 296     {}
 297
 298     // Support for l-value reference proxy copy construction
 299     template <typename E2, typename L2>
 300     homogeneous_color_base(homogeneous_color_base<E2, L2, 4>& c)
 301         : v0_(gil::at_c<mapping_transform<Layout, L2, 0>::value>(c))
 302         , v1_(gil::at_c<mapping_transform<Layout, L2, 1>::value>(c))
 303         , v2_(gil::at_c<mapping_transform<Layout, L2, 2>::value>(c))
 304         , v3_(gil::at_c<mapping_transform<Layout, L2, 3>::value>(c))
 305     {}
 306
 307     // Support for planar_pixel_iterator construction and dereferencing
 308     template <typename P>
 309     homogeneous_color_base(P * p, bool)
 310         : v0_(&semantic_at_c<0>(*p))
 311         , v1_(&semantic_at_c<1>(*p))
 312         , v2_(&semantic_at_c<2>(*p))
 313         , v3_(&semantic_at_c<3>(*p))
 314     {}
 315
 316     // Support for planar_pixel_reference offset constructor
 317     template <typename Ptr>
 318     homogeneous_color_base(Ptr const& ptr, std::ptrdiff_t diff)
 319         : v0_(*memunit_advanced(semantic_at_c<0>(ptr), diff))
 320         , v1_(*memunit_advanced(semantic_at_c<1>(ptr), diff))
 321         , v2_(*memunit_advanced(semantic_at_c<2>(ptr), diff))
 322         , v3_(*memunit_advanced(semantic_at_c<3>(ptr), diff))
 323     {}
 324
 325     template <typename Ref>
 326     Ref deref() const
 327     {
 328         return Ref(
 329             *semantic_at_c<0>(*this),
 330             *semantic_at_c<1>(*this),
 331             *semantic_at_c<2>(*this),
 332             *semantic_at_c<3>(*this));
 333     }
 334
 335     auto at(std::integral_constant<int, 0>)
 336         -> typename element_reference_type<homogeneous_color_base>::type
 337     { return v0_; }
 338
 339     auto at(std::integral_constant<int, 0>) const
 340         -> typename element_const_reference_type<homogeneous_color_base>::type
 341     { return v0_; }
 342
 343     auto at(std::integral_constant<int, 1>)
 344         -> typename element_reference_type<homogeneous_color_base>::type
 345     { return v1_; }
 346
 347     auto at(std::integral_constant<int, 1>) const
 348         -> typename element_const_reference_type<homogeneous_color_base>::type
 349     { return v1_; }
 350
 351     auto at(std::integral_constant<int, 2>)
 352         -> typename element_reference_type<homogeneous_color_base>::type
 353     { return v2_; }
 354
 355     auto at(std::integral_constant<int, 2>) const
 356         -> typename element_const_reference_type<homogeneous_color_base>::type
 357     { return v2_; }
 358
 359     auto at(std::integral_constant<int, 3>)
 360         -> typename element_reference_type<homogeneous_color_base>::type
 361     { return v3_; }
 362
 363     auto at(std::integral_constant<int, 3>) const
 364         -> typename element_const_reference_type<homogeneous_color_base>::type
 365     { return v3_; }
 366
 367     // Support for planar_pixel_reference operator[]
 368     Element at_c_dynamic(std::size_t i) const
 369     {
 370         switch (i)
 371         {
 372         case 0: return v0_;
 373         case 1: return v1_;
 374         case 2: return v2_;
 375         }
 376         return v3_;
 377     }
 378
 379 private:
 380     Element v0_{};
 381     Element v1_{};
 382     Element v2_{};
 383     Element v3_{};
 384 };
 385
 386 /// \brief A homogeneous color base holding five color elements.
 387 /// Models HomogeneousColorBaseConcept or HomogeneousColorBaseValueConcept
 388 /// \ingroup ColorBaseModelHomogeneous
 389 template <typename Element, typename Layout>
 390 struct homogeneous_color_base<Element, Layout, 5>
 391 {
 392     using layout_t = Layout;
 393
 394     homogeneous_color_base() = default;
 395     explicit homogeneous_color_base(Element v)
 396         : v0_(v), v1_(v), v2_(v), v3_(v), v4_(v)
 397     {}
 398
 399     homogeneous_color_base(Element v0, Element v1, Element v2, Element v3, Element v4)
 400         : v0_(v0), v1_(v1), v2_(v2), v3_(v3), v4_(v4)
 401     {}
 402
 403     template <typename E2, typename L2>
 404     homogeneous_color_base(homogeneous_color_base<E2, L2, 5> const& c)
 405         : v0_(gil::at_c<mapping_transform<Layout, L2, 0>::value>(c))
 406         , v1_(gil::at_c<mapping_transform<Layout, L2, 1>::value>(c))
 407         , v2_(gil::at_c<mapping_transform<Layout, L2, 2>::value>(c))
 408         , v3_(gil::at_c<mapping_transform<Layout, L2, 3>::value>(c))
 409         , v4_(gil::at_c<mapping_transform<Layout, L2, 4>::value>(c))
 410     {}
 411
 412     // Support for l-value reference proxy copy construction
 413     template <typename E2, typename L2>
 414     homogeneous_color_base(homogeneous_color_base<E2, L2, 5>& c)
 415         : v0_(gil::at_c<mapping_transform<Layout, L2, 0>::value>(c))
 416         , v1_(gil::at_c<mapping_transform<Layout, L2, 1>::value>(c))
 417         , v2_(gil::at_c<mapping_transform<Layout, L2, 2>::value>(c))
 418         , v3_(gil::at_c<mapping_transform<Layout, L2, 3>::value>(c))
 419         , v4_(gil::at_c<mapping_transform<Layout, L2, 4>::value>(c))
 420     {}
 421
 422     // Support for planar_pixel_iterator construction and dereferencing
 423     template <typename P>
 424     homogeneous_color_base(P* p, bool)
 425         : v0_(&semantic_at_c<0>(*p))
 426         , v1_(&semantic_at_c<1>(*p))
 427         , v2_(&semantic_at_c<2>(*p))
 428         , v3_(&semantic_at_c<3>(*p))
 429         , v4_(&semantic_at_c<4>(*p))
 430     {}
 431
 432     // Support for planar_pixel_reference offset constructor
 433     template <typename Ptr>
 434     homogeneous_color_base(Ptr const& ptr, std::ptrdiff_t diff)
 435         : v0_(*memunit_advanced(semantic_at_c<0>(ptr), diff))
 436         , v1_(*memunit_advanced(semantic_at_c<1>(ptr), diff))
 437         , v2_(*memunit_advanced(semantic_at_c<2>(ptr), diff))
 438         , v3_(*memunit_advanced(semantic_at_c<3>(ptr), diff))
 439         , v4_(*memunit_advanced(semantic_at_c<4>(ptr), diff))
 440     {}
 441
 442
 443     auto at(std::integral_constant<int, 0>)
 444         -> typename element_reference_type<homogeneous_color_base>::type
 445     { return v0_; }
 446
 447     auto at(std::integral_constant<int, 0>) const
 448         -> typename element_const_reference_type<homogeneous_color_base>::type
 449     { return v0_; }
 450
 451     auto at(std::integral_constant<int, 1>)
 452         -> typename element_reference_type<homogeneous_color_base>::type
 453     { return v1_; }
 454
 455     auto at(std::integral_constant<int, 1>) const
 456         -> typename element_const_reference_type<homogeneous_color_base>::type
 457     { return v1_; }
 458
 459     auto at(std::integral_constant<int, 2>)
 460         -> typename element_reference_type<homogeneous_color_base>::type
 461     { return v2_; }
 462
 463     auto at(std::integral_constant<int, 2>) const
 464         -> typename element_const_reference_type<homogeneous_color_base>::type
 465     { return v2_; }
 466
 467     auto at(std::integral_constant<int, 3>)
 468         -> typename element_reference_type<homogeneous_color_base>::type
 469     { return v3_; }
 470
 471     auto at(std::integral_constant<int, 3>) const
 472         -> typename element_const_reference_type<homogeneous_color_base>::type
 473     { return v3_; }
 474
 475     auto at(std::integral_constant<int, 4>)
 476         -> typename element_reference_type<homogeneous_color_base>::type
 477     { return v4_; }
 478
 479     auto at(std::integral_constant<int, 4>) const
 480         -> typename element_const_reference_type<homogeneous_color_base>::type
 481     { return v4_; }
 482
 483     template <typename Ref>
 484     Ref deref() const
 485     {
 486         return Ref(
 487             *semantic_at_c<0>(*this),
 488             *semantic_at_c<1>(*this),
 489             *semantic_at_c<2>(*this),
 490             *semantic_at_c<3>(*this),
 491             *semantic_at_c<4>(*this));
 492     }
 493
 494     // Support for planar_pixel_reference operator[]
 495     Element at_c_dynamic(std::size_t i) const
 496     {
 497         switch (i)
 498         {
 499         case 0: return v0_;
 500         case 1: return v1_;
 501         case 2: return v2_;
 502         case 3: return v3_;
 503         }
 504         return v4_;
 505     }
 506
 507 private:
 508     Element v0_{};
 509     Element v1_{};
 510     Element v2_{};
 511     Element v3_{};
 512     Element v4_{};
 513 };
 514
 515 #if BOOST_WORKAROUND(BOOST_MSVC, >= 1400)
 516 #pragma warning(pop)
 517 #endif
 518
 519 // The following way of casting adjacent channels (the contents of color_base) into an array appears to be unsafe
 520 // -- there is no guarantee that the compiler won't add any padding between adjacent channels.
 521 // Note, however, that GIL _must_ be compiled with compiler settings ensuring there is no padding in the color base structs.
 522 // This is because the color base structs must model the interleaved organization in memory. In other words, the client may
 523 // have existing RGB image in the form "RGBRGBRGB..." and we must be able to represent it with an array of RGB color bases (i.e. RGB pixels)
 524 // with no padding. We have tested with char/int/float/double channels on gcc and VC and have so far discovered no problem.
 525 // We have even tried using strange channels consisting of short + char (3 bytes). With the default 4-byte alignment on VC, the size
 526 // of this channel is padded to 4 bytes, so an RGB pixel of it will be 4x3=12 bytes. The code below will still work properly.
 527 // However, the client must nevertheless ensure that proper compiler settings are used for their compiler and their channel types.
 528
 529 template <typename Element, typename Layout, int K>
 530 auto dynamic_at_c(homogeneous_color_base<Element,Layout,K>& cb, std::size_t i)
 531     -> typename element_reference_type<homogeneous_color_base<Element, Layout, K>>::type
 532 {
 533     BOOST_ASSERT(i < K);
 534     return (gil_reinterpret_cast<Element*>(&cb))[i];
 535 }
 536
 537 template <typename Element, typename Layout, int K>
 538 auto dynamic_at_c(homogeneous_color_base<Element, Layout, K> const& cb, std::size_t i)
 539     -> typename element_const_reference_type
 540         <
 541             homogeneous_color_base<Element, Layout, K>
 542         >::type
 543 {
 544     BOOST_ASSERT(i < K);
 545     return (gil_reinterpret_cast_c<const Element*>(&cb))[i];
 546 }
 547
 548 template <typename Element, typename Layout, int K>
 549 auto dynamic_at_c(homogeneous_color_base<Element&, Layout, K> const& cb, std::size_t i)
 550     -> typename element_reference_type
 551         <
 552             homogeneous_color_base<Element&, Layout, K>
 553         >::type
 554 {
 555     BOOST_ASSERT(i < K);
 556     return cb.at_c_dynamic(i);
 557 }
 558
 559 template <typename Element, typename Layout, int K>
 560 auto dynamic_at_c(
 561     homogeneous_color_base<Element const&, Layout, K>const& cb, std::size_t i)
 562     -> typename element_const_reference_type
 563         <
 564             homogeneous_color_base<Element const&, Layout, K>
 565         >::type
 566 {
 567     BOOST_ASSERT(i < K);
 568     return cb.at_c_dynamic(i);
 569 }
 570
 571 } // namespace detail
 572
 573 template <typename Element, typename Layout, int K1, int K>
 574 struct kth_element_type<detail::homogeneous_color_base<Element, Layout, K1>, K>
 575 {
 576     using type = Element;
 577 };
 578
 579 template <typename Element, typename Layout, int K1, int K>
 580 struct kth_element_reference_type<detail::homogeneous_color_base<Element, Layout, K1>, K>
 581     : std::add_lvalue_reference<Element>
 582 {};
 583
 584 template <typename Element, typename Layout, int K1, int K>
 585 struct kth_element_const_reference_type
 586     <
 587         detail::homogeneous_color_base<Element, Layout, K1>,
 588         K
 589     >
 590     : std::add_lvalue_reference<typename std::add_const<Element>::type>
 591 {};
 592
 593 /// \brief Provides mutable access to the K-th element, in physical order
 594 /// \ingroup ColorBaseModelHomogeneous
 595 template <int K, typename E, typename L, int N>
 596 inline
 597 auto at_c(detail::homogeneous_color_base<E, L, N>& p)
 598     -> typename std::add_lvalue_reference<E>::type
 599 {
 600     return p.at(std::integral_constant<int, K>());
 601 }
 602
 603 /// \brief Provides constant access to the K-th element, in physical order
 604 /// \ingroup ColorBaseModelHomogeneous
 605 template <int K, typename E, typename L, int N>
 606 inline
 607 auto at_c(const detail::homogeneous_color_base<E, L, N>& p)
 608     -> typename std::add_lvalue_reference<typename std::add_const<E>::type>::type
 609 {
 610     return p.at(std::integral_constant<int, K>());
 611 }
 612
 613 namespace detail
 614 {
 615
 616 struct swap_fn
 617 {
 618     template <typename T>
 619     void operator()(T& x, T& y) const
 620     {
 621         using std::swap;
 622         swap(x, y);
 623     }
 624 };
 625
 626 } // namespace detail
 627
 628 template <typename E, typename L, int N>
 629 inline
 630 void swap(
 631     detail::homogeneous_color_base<E, L, N>& x,
 632     detail::homogeneous_color_base<E, L, N>& y)
 633 {
 634     static_for_each(x, y, detail::swap_fn());
 635 }
 636
 637 }}  // namespace boost::gil
 638
 639 #endif