1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
// Copyright (c) 2016 The vulkano developers
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or http://opensource.org/licenses/MIT>,
// at your option. All files in the project carrying such
// notice may not be copied, modified, or distributed except
// according to those terms.

//! Description of a single descriptor.
//!
//! This module contains traits and structs related to describing a single descriptor. A descriptor
//! is a slot where you can bind a buffer or an image so that it can be accessed from your shaders.
//! In order to specify which buffer or image to bind to a descriptor, see the `descriptor_set`
//! module.
//!
//! There are four different kinds of descriptors that give access to buffers:
//!
//! - Uniform texel buffers. Gives read-only access to the content of a buffer. Only supports
//!   certain buffer formats.
//! - Storage texel buffers. Gives read and/or write access to the content of a buffer. Only
//!   supports certain buffer formats. Less restrictive but sometimes slower than uniform texel
//!   buffers.
//! - Uniform buffers. Gives read-only access to the content of a buffer. Less restrictive but
//!   sometimes slower than uniform texel buffers.
//! - Storage buffers. Gives read and/or write access to the content of a buffer. Less restrictive
//!   but sometimes slower than uniform buffers and storage texel buffers.
//!
//! There are five different kinds of descriptors related to images:
//!
//! - Storage images. Gives read and/or write access to individual pixels in an image. The image
//!   cannot be sampled. In other words, you have exactly specify which pixel to read or write.
//! - Sampled images. Gives read-only access to an image. Before you can use a sampled image in a
//!   a shader, you have to combine it with a sampler (see below). The sampler describes how
//!   reading the image will behave.
//! - Samplers. Doesn't contain an image but a sampler object that describes how an image will be
//!   accessed. This is meant to be combined with a sampled image (see above).
//! - Combined image and sampler. Similar to a sampled image, but also directly includes the
//!   sampler which indicates how the sampling is done.
//! - Input attachments. The fastest but also most restrictive access to images. Must be integrated
//!   in a render pass. Can only give access to the same pixel as the one you're processing.
//!

use format::Format;
use image::Dimensions;
use std::cmp;
use std::error;
use std::fmt;
use std::ops::BitOr;
use sync::AccessFlagBits;
use sync::PipelineStages;
use vk;

/// Contains the exact description of a single descriptor.
///
/// > **Note**: You are free to fill a `DescriptorDesc` struct the way you want, but its validity
/// > will be checked when you create a pipeline layout, a descriptor set, or when you try to bind
/// > a descriptor set.
// TODO: add example
#[derive(Debug, Clone)]
pub struct DescriptorDesc {
    /// Describes the content and layout of each array element of a descriptor.
    pub ty: DescriptorDescTy,

    /// How many array elements this descriptor is made of. The value 0 is invalid and may trigger
    /// a panic depending on the situation.
    pub array_count: u32,

    /// Which shader stages are going to access this descriptor.
    pub stages: ShaderStages,

    /// True if the attachment is only ever read by the shader. False if it is also written.
    pub readonly: bool,
}

impl DescriptorDesc {
    /// Checks whether we are a superset of another descriptor.
    ///
    /// Returns true if `self` is the same descriptor as `other`, or if `self` is the same as
    /// `other` but with a larger array elements count and/or more shader stages.
    // TODO: add example
    #[inline]
    pub fn is_superset_of(&self, other: &DescriptorDesc)
                          -> Result<(), DescriptorDescSupersetError> {
        self.ty.is_superset_of(&other.ty)?;
        self.stages.is_superset_of(&other.stages)?;

        if self.array_count < other.array_count {
            return Err(DescriptorDescSupersetError::ArrayTooSmall {
                           len: self.array_count,
                           required: other.array_count,
                       });
        }

        if self.readonly && !other.readonly {
            return Err(DescriptorDescSupersetError::MutabilityRequired);
        }

        Ok(())
    }

    /// Builds a `DescriptorDesc` that is the union of `self` and `other`, if possible.
    ///
    /// The returned value will be a superset of both `self` and `other`.
    // TODO: Result instead of Option
    // TODO: add example
    #[inline]
    pub fn union(&self, other: &DescriptorDesc) -> Option<DescriptorDesc> {
        if self.ty != other.ty {
            return None;
        }

        Some(DescriptorDesc {
                 ty: self.ty.clone(),
                 array_count: cmp::max(self.array_count, other.array_count),
                 stages: self.stages | other.stages,
                 readonly: self.readonly && other.readonly,
             })
    }

    /// Returns the pipeline stages and access flags corresponding to the usage of this descriptor.
    ///
    /// # Panic
    ///
    /// Panics if the type is `Sampler`.
    ///
    pub fn pipeline_stages_and_access(&self) -> (PipelineStages, AccessFlagBits) {
        let stages: PipelineStages = self.stages.into();

        let access = match self.ty {
            DescriptorDescTy::Sampler => panic!(),
            DescriptorDescTy::CombinedImageSampler(_) |
            DescriptorDescTy::Image(_) => {
                AccessFlagBits {
                    shader_read: true,
                    shader_write: !self.readonly,
                    ..AccessFlagBits::none()
                }
            },
            DescriptorDescTy::TexelBuffer { .. } => {
                AccessFlagBits {
                    shader_read: true,
                    shader_write: !self.readonly,
                    ..AccessFlagBits::none()
                }
            },
            DescriptorDescTy::InputAttachment { .. } => {
                AccessFlagBits {
                    input_attachment_read: true,
                    ..AccessFlagBits::none()
                }
            },
            DescriptorDescTy::Buffer(ref buf) => {
                if buf.storage {
                    AccessFlagBits {
                        shader_read: true,
                        shader_write: !self.readonly,
                        ..AccessFlagBits::none()
                    }
                } else {
                    AccessFlagBits {
                        uniform_read: true,
                        ..AccessFlagBits::none()
                    }
                }
            },
        };

        (stages, access)
    }
}

/// Describes the content and layout of each array element of a descriptor.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum DescriptorDescTy {
    Sampler, // TODO: the sampler has some restrictions as well
    CombinedImageSampler(DescriptorImageDesc), // TODO: the sampler has some restrictions as well
    Image(DescriptorImageDesc),
    TexelBuffer {
        /// If `true`, this describes a storage texel buffer.
        storage: bool,

        /// The format of the content, or `None` if the format is unknown. Depending on the
        /// context, it may be invalid to have a `None` value here. If the format is `Some`, only
        /// buffer views that have this exact format can be attached to this descriptor.
        format: Option<Format>,
    },
    InputAttachment {
        /// If `true`, the input attachment is multisampled. Only multisampled images can be
        /// attached to this descriptor. If `false`, only single-sampled images can be attached.
        multisampled: bool,
        array_layers: DescriptorImageDescArray,
    },
    Buffer(DescriptorBufferDesc),
}

impl DescriptorDescTy {
    /// Returns the type of descriptor.
    ///
    /// Returns `None` if there's not enough info to determine the type.
    // TODO: add example
    pub fn ty(&self) -> Option<DescriptorType> {
        Some(match *self {
                 DescriptorDescTy::Sampler => DescriptorType::Sampler,
                 DescriptorDescTy::CombinedImageSampler(_) => DescriptorType::CombinedImageSampler,
                 DescriptorDescTy::Image(ref desc) => {
                     if desc.sampled {
                         DescriptorType::SampledImage
                     } else {
                         DescriptorType::StorageImage
                     }
                 },
                 DescriptorDescTy::InputAttachment { .. } => DescriptorType::InputAttachment,
                 DescriptorDescTy::Buffer(ref desc) => {
                     let dynamic = match desc.dynamic {
                         Some(d) => d,
                         None => return None,
                     };
                     match (desc.storage, dynamic) {
                         (false, false) => DescriptorType::UniformBuffer,
                         (true, false) => DescriptorType::StorageBuffer,
                         (false, true) => DescriptorType::UniformBufferDynamic,
                         (true, true) => DescriptorType::StorageBufferDynamic,
                     }
                 },
                 DescriptorDescTy::TexelBuffer { storage, .. } => {
                     if storage {
                         DescriptorType::StorageTexelBuffer
                     } else {
                         DescriptorType::UniformTexelBuffer
                     }
                 },
             })
    }

    /// Checks whether we are a superset of another descriptor type.
    // TODO: add example
    #[inline]
    pub fn is_superset_of(&self, other: &DescriptorDescTy)
                          -> Result<(), DescriptorDescSupersetError> {
        match (self, other) {
            (&DescriptorDescTy::Sampler, &DescriptorDescTy::Sampler) => Ok(()),

            (&DescriptorDescTy::CombinedImageSampler(ref me),
             &DescriptorDescTy::CombinedImageSampler(ref other)) => me.is_superset_of(other),

            (&DescriptorDescTy::Image(ref me), &DescriptorDescTy::Image(ref other)) =>
                me.is_superset_of(other),

            (&DescriptorDescTy::InputAttachment {
                 multisampled: me_multisampled,
                 array_layers: me_array_layers,
             },
             &DescriptorDescTy::InputAttachment {
                 multisampled: other_multisampled,
                 array_layers: other_array_layers,
             }) => {
                if me_multisampled != other_multisampled {
                    return Err(DescriptorDescSupersetError::MultisampledMismatch {
                                   provided: me_multisampled,
                                   expected: other_multisampled,
                               });
                }

                if me_array_layers != other_array_layers {
                    return Err(DescriptorDescSupersetError::IncompatibleArrayLayers {
                                   provided: me_array_layers,
                                   required: other_array_layers,
                               });
                }

                Ok(())
            },

            (&DescriptorDescTy::Buffer(ref me), &DescriptorDescTy::Buffer(ref other)) => {
                if me.storage != other.storage {
                    return Err(DescriptorDescSupersetError::TypeMismatch);
                }

                match (me.dynamic, other.dynamic) {
                    (Some(_), None) => Ok(()),
                    (Some(m), Some(o)) => if m == o {
                        Ok(())
                    } else {
                        Err(DescriptorDescSupersetError::TypeMismatch)
                    },
                    (None, None) => Ok(()),
                    (None, Some(_)) => Err(DescriptorDescSupersetError::TypeMismatch),
                }
            },

            (&DescriptorDescTy::TexelBuffer {
                 storage: me_storage,
                 format: me_format,
             },
             &DescriptorDescTy::TexelBuffer {
                 storage: other_storage,
                 format: other_format,
             }) => {
                if me_storage != other_storage {
                    return Err(DescriptorDescSupersetError::TypeMismatch);
                }

                match (me_format, other_format) {
                    (Some(_), None) => Ok(()),
                    (Some(m), Some(o)) => if m == o {
                        Ok(())
                    } else {
                        Err(DescriptorDescSupersetError::FormatMismatch {
                                provided: Some(m),
                                expected: o,
                            })
                    },
                    (None, None) => Ok(()),
                    (None, Some(a)) => Err(DescriptorDescSupersetError::FormatMismatch {
                                               provided: Some(a),
                                               expected: a,
                                           }),
                }
            },

            // Any other combination is invalid.
            _ => Err(DescriptorDescSupersetError::TypeMismatch),
        }
    }
}

/// Additional description for descriptors that contain images.
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub struct DescriptorImageDesc {
    /// If `true`, the image can be sampled by the shader. Only images that were created with the
    /// `sampled` usage can be attached to the descriptor.
    pub sampled: bool,
    /// The kind of image: one-dimensional, two-dimensional, three-dimensional, or cube.
    pub dimensions: DescriptorImageDescDimensions,
    /// The format of the image, or `None` if the format is unknown. If `Some`, only images with
    /// exactly that format can be attached.
    pub format: Option<Format>,
    /// True if the image is multisampled.
    pub multisampled: bool,
    /// Whether the descriptor contains one or more array layers of an image.
    pub array_layers: DescriptorImageDescArray,
}

impl DescriptorImageDesc {
    /// Checks whether we are a superset of another image.
    // TODO: add example
    #[inline]
    pub fn is_superset_of(&self, other: &DescriptorImageDesc)
                          -> Result<(), DescriptorDescSupersetError> {
        if self.dimensions != other.dimensions {
            return Err(DescriptorDescSupersetError::DimensionsMismatch {
                           provided: self.dimensions,
                           expected: other.dimensions,
                       });
        }

        if self.multisampled != other.multisampled {
            return Err(DescriptorDescSupersetError::MultisampledMismatch {
                           provided: self.multisampled,
                           expected: other.multisampled,
                       });
        }

        match (self.format, other.format) {
            (Some(a), Some(b)) => if a != b {
                return Err(DescriptorDescSupersetError::FormatMismatch {
                               provided: Some(a),
                               expected: b,
                           });
            },
            (Some(_), None) => (),
            (None, None) => (),
            (None, Some(a)) => {
                return Err(DescriptorDescSupersetError::FormatMismatch {
                               provided: None,
                               expected: a,
                           });
            },
        };

        match (self.array_layers, other.array_layers) {
            (DescriptorImageDescArray::NonArrayed, DescriptorImageDescArray::NonArrayed) => (),
            (DescriptorImageDescArray::Arrayed { max_layers: my_max },
             DescriptorImageDescArray::Arrayed { max_layers: other_max }) => {
                match (my_max, other_max) {
                    (Some(m), Some(o)) => if m < o {
                        return Err(DescriptorDescSupersetError::IncompatibleArrayLayers {
                                       provided: DescriptorImageDescArray::Arrayed {
                                           max_layers: my_max,
                                       },
                                       required: DescriptorImageDescArray::Arrayed {
                                           max_layers: other_max,
                                       },
                                   });
                    },
                    (Some(_), None) => (),
                    (None, Some(m)) => {
                        return Err(DescriptorDescSupersetError::IncompatibleArrayLayers {
                                       provided: DescriptorImageDescArray::Arrayed {
                                           max_layers: my_max,
                                       },
                                       required: DescriptorImageDescArray::Arrayed {
                                           max_layers: other_max,
                                       },
                                   });
                    },
                    (None, None) => (),     // TODO: is this correct?
                };
            },
            (a, b) => return Err(DescriptorDescSupersetError::IncompatibleArrayLayers {
                                     provided: a,
                                     required: b,
                                 }),
        };

        Ok(())
    }
}

// TODO: documentation
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub enum DescriptorImageDescArray {
    NonArrayed,
    Arrayed { max_layers: Option<u32> },
}

// TODO: documentation
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub enum DescriptorImageDescDimensions {
    OneDimensional,
    TwoDimensional,
    ThreeDimensional,
    Cube,
}

impl DescriptorImageDescDimensions {
    /// Builds the `DescriptorImageDescDimensions` that corresponds to actual dimensions.
    #[inline]
    pub fn from_dimensions(dims: Dimensions) -> DescriptorImageDescDimensions {
        match dims {
            Dimensions::Dim1d { .. } => DescriptorImageDescDimensions::OneDimensional,
            Dimensions::Dim1dArray { .. } => DescriptorImageDescDimensions::OneDimensional,
            Dimensions::Dim2d { .. } => DescriptorImageDescDimensions::TwoDimensional,
            Dimensions::Dim2dArray { .. } => DescriptorImageDescDimensions::TwoDimensional,
            Dimensions::Dim3d { .. } => DescriptorImageDescDimensions::ThreeDimensional,
            Dimensions::Cubemap { .. } => DescriptorImageDescDimensions::Cube,
            Dimensions::CubemapArray { .. } => DescriptorImageDescDimensions::Cube,
        }
    }
}

// TODO: documentation
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct DescriptorBufferDesc {
    pub dynamic: Option<bool>,
    pub storage: bool,
}

/// Describes what kind of resource may later be bound to a descriptor.
///
/// This is mostly the same as a `DescriptorDescTy` but with less precise information.
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
#[repr(u32)]
pub enum DescriptorType {
    Sampler = vk::DESCRIPTOR_TYPE_SAMPLER,
    CombinedImageSampler = vk::DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER,
    SampledImage = vk::DESCRIPTOR_TYPE_SAMPLED_IMAGE,
    StorageImage = vk::DESCRIPTOR_TYPE_STORAGE_IMAGE,
    UniformTexelBuffer = vk::DESCRIPTOR_TYPE_UNIFORM_TEXEL_BUFFER,
    StorageTexelBuffer = vk::DESCRIPTOR_TYPE_STORAGE_TEXEL_BUFFER,
    UniformBuffer = vk::DESCRIPTOR_TYPE_UNIFORM_BUFFER,
    StorageBuffer = vk::DESCRIPTOR_TYPE_STORAGE_BUFFER,
    UniformBufferDynamic = vk::DESCRIPTOR_TYPE_UNIFORM_BUFFER_DYNAMIC,
    StorageBufferDynamic = vk::DESCRIPTOR_TYPE_STORAGE_BUFFER_DYNAMIC,
    InputAttachment = vk::DESCRIPTOR_TYPE_INPUT_ATTACHMENT,
}

/// Error when checking whether a descriptor is a superset of another one.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum DescriptorDescSupersetError {
    /// The number of array elements of the descriptor is smaller than expected.
    ArrayTooSmall { len: u32, required: u32 },

    /// The descriptor type doesn't match the type of the other descriptor.
    TypeMismatch,

    /// The descriptor is marked as read-only, but the other is not.
    MutabilityRequired,

    /// The shader stages are not a superset of one another.
    ShaderStagesNotSuperset,

    DimensionsMismatch {
        provided: DescriptorImageDescDimensions,
        expected: DescriptorImageDescDimensions,
    },

    FormatMismatch {
        provided: Option<Format>,
        expected: Format,
    },

    MultisampledMismatch { provided: bool, expected: bool },

    IncompatibleArrayLayers {
        provided: DescriptorImageDescArray,
        required: DescriptorImageDescArray,
    },
}

impl error::Error for DescriptorDescSupersetError {
    #[inline]
    fn description(&self) -> &str {
        match *self {
            DescriptorDescSupersetError::ArrayTooSmall { .. } => {
                "the number of array elements of the descriptor is smaller than expected"
            },
            DescriptorDescSupersetError::TypeMismatch => {
                "the descriptor type doesn't match the type of the other descriptor"
            },
            DescriptorDescSupersetError::MutabilityRequired => {
                "the descriptor is marked as read-only, but the other is not"
            },
            DescriptorDescSupersetError::ShaderStagesNotSuperset => {
                "the shader stages are not a superset of one another"
            },
            DescriptorDescSupersetError::DimensionsMismatch { .. } => {
                "mismatch between the dimensions of the two descriptors"
            },
            DescriptorDescSupersetError::FormatMismatch { .. } => {
                "mismatch between the format of the two descriptors"
            },
            DescriptorDescSupersetError::MultisampledMismatch { .. } => {
                "mismatch between whether the descriptors are multisampled"
            },
            DescriptorDescSupersetError::IncompatibleArrayLayers { .. } => {
                "the array layers of the descriptors aren't compatible"
            },
        }
    }
}

impl fmt::Display for DescriptorDescSupersetError {
    #[inline]
    fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        write!(fmt, "{}", error::Error::description(self))
    }
}

impl From<ShaderStagesSupersetError> for DescriptorDescSupersetError {
    #[inline]
    fn from(err: ShaderStagesSupersetError) -> DescriptorDescSupersetError {
        match err {
            ShaderStagesSupersetError::NotSuperset => {
                DescriptorDescSupersetError::ShaderStagesNotSuperset
            },
        }
    }
}

/// Describes which shader stages have access to a descriptor.
// TODO: add example with BitOr
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub struct ShaderStages {
    /// `True` means that the descriptor will be used by the vertex shader.
    pub vertex: bool,
    /// `True` means that the descriptor will be used by the tessellation control shader.
    pub tessellation_control: bool,
    /// `True` means that the descriptor will be used by the tessellation evaluation shader.
    pub tessellation_evaluation: bool,
    /// `True` means that the descriptor will be used by the geometry shader.
    pub geometry: bool,
    /// `True` means that the descriptor will be used by the fragment shader.
    pub fragment: bool,
    /// `True` means that the descriptor will be used by the compute shader.
    pub compute: bool,
}

impl ShaderStages {
    /// Creates a `ShaderStages` struct will all stages set to `true`.
    // TODO: add example
    #[inline]
    pub fn all() -> ShaderStages {
        ShaderStages {
            vertex: true,
            tessellation_control: true,
            tessellation_evaluation: true,
            geometry: true,
            fragment: true,
            compute: true,
        }
    }

    /// Creates a `ShaderStages` struct will all stages set to `false`.
    // TODO: add example
    #[inline]
    pub fn none() -> ShaderStages {
        ShaderStages {
            vertex: false,
            tessellation_control: false,
            tessellation_evaluation: false,
            geometry: false,
            fragment: false,
            compute: false,
        }
    }

    /// Creates a `ShaderStages` struct with all graphics stages set to `true`.
    // TODO: add example
    #[inline]
    pub fn all_graphics() -> ShaderStages {
        ShaderStages {
            vertex: true,
            tessellation_control: true,
            tessellation_evaluation: true,
            geometry: true,
            fragment: true,
            compute: false,
        }
    }

    /// Creates a `ShaderStages` struct with the compute stage set to `true`.
    // TODO: add example
    #[inline]
    pub fn compute() -> ShaderStages {
        ShaderStages {
            vertex: false,
            tessellation_control: false,
            tessellation_evaluation: false,
            geometry: false,
            fragment: false,
            compute: true,
        }
    }

    /// Checks whether we have more stages enabled than `other`.
    // TODO: add example
    #[inline]
    pub fn is_superset_of(&self, other: &ShaderStages) -> Result<(), ShaderStagesSupersetError> {
        if (self.vertex || !other.vertex) &&
            (self.tessellation_control || !other.tessellation_control) &&
            (self.tessellation_evaluation || !other.tessellation_evaluation) &&
            (self.geometry || !other.geometry) &&
            (self.fragment || !other.fragment) && (self.compute || !other.compute)
        {
            Ok(())
        } else {
            Err(ShaderStagesSupersetError::NotSuperset)
        }
    }

    /// Checks whether any of the stages in `self` are also present in `other`.
    // TODO: add example
    #[inline]
    pub fn intersects(&self, other: &ShaderStages) -> bool {
        (self.vertex && other.vertex) ||
            (self.tessellation_control && other.tessellation_control) ||
            (self.tessellation_evaluation && other.tessellation_evaluation) ||
            (self.geometry && other.geometry) || (self.fragment && other.fragment) ||
            (self.compute && other.compute)
    }

    #[inline]
    pub(crate) fn into_vulkan_bits(self) -> vk::ShaderStageFlags {
        let mut result = 0;
        if self.vertex {
            result |= vk::SHADER_STAGE_VERTEX_BIT;
        }
        if self.tessellation_control {
            result |= vk::SHADER_STAGE_TESSELLATION_CONTROL_BIT;
        }
        if self.tessellation_evaluation {
            result |= vk::SHADER_STAGE_TESSELLATION_EVALUATION_BIT;
        }
        if self.geometry {
            result |= vk::SHADER_STAGE_GEOMETRY_BIT;
        }
        if self.fragment {
            result |= vk::SHADER_STAGE_FRAGMENT_BIT;
        }
        if self.compute {
            result |= vk::SHADER_STAGE_COMPUTE_BIT;
        }
        result
    }
}

impl BitOr for ShaderStages {
    type Output = ShaderStages;

    #[inline]
    fn bitor(self, other: ShaderStages) -> ShaderStages {
        ShaderStages {
            vertex: self.vertex || other.vertex,
            tessellation_control: self.tessellation_control || other.tessellation_control,
            tessellation_evaluation: self.tessellation_evaluation || other.tessellation_evaluation,
            geometry: self.geometry || other.geometry,
            fragment: self.fragment || other.fragment,
            compute: self.compute || other.compute,
        }
    }
}

impl From<ShaderStages> for PipelineStages {
    #[inline]
    fn from(stages: ShaderStages) -> PipelineStages {
        PipelineStages {
            vertex_shader: stages.vertex,
            tessellation_control_shader: stages.tessellation_control,
            tessellation_evaluation_shader: stages.tessellation_evaluation,
            geometry_shader: stages.geometry,
            fragment_shader: stages.fragment,
            compute_shader: stages.compute,
            ..PipelineStages::none()
        }
    }
}

/// Error when checking whether some shader stages are superset of others.
#[derive(Debug, Clone)]
pub enum ShaderStagesSupersetError {
    NotSuperset,
}

impl error::Error for ShaderStagesSupersetError {
    #[inline]
    fn description(&self) -> &str {
        match *self {
            ShaderStagesSupersetError::NotSuperset => {
                "shader stages not a superset"
            },
        }
    }
}

impl fmt::Display for ShaderStagesSupersetError {
    #[inline]
    fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        write!(fmt, "{}", error::Error::description(self))
    }
}