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
use crate::{texture, Document};

pub use json::material::AlphaMode;
#[cfg(feature = "extensions")]
use serde_json::{Map, Value};

lazy_static! {
    static ref DEFAULT_MATERIAL: json::material::Material = Default::default();
}

/// The material appearance of a primitive.
#[derive(Clone, Debug)]
pub struct Material<'a> {
    /// The parent `Document` struct.
    document: &'a Document,

    /// The corresponding JSON index - `None` when the default material.
    index: Option<usize>,

    /// The corresponding JSON struct.
    json: &'a json::material::Material,
}

impl<'a> Material<'a> {
    /// Constructs a `Material`.
    pub(crate) fn new(
        document: &'a Document,
        index: usize,
        json: &'a json::material::Material,
    ) -> Self {
        Self {
            document,
            index: Some(index),
            json,
        }
    }

    /// Constructs the default `Material`.
    pub(crate) fn default(document: &'a Document) -> Self {
        Self {
            document,
            index: None,
            json: &DEFAULT_MATERIAL,
        }
    }

    /// Returns the internal JSON index if this `Material` was explicity defined.
    ///
    /// This function returns `None` if the `Material` is the default material.
    pub fn index(&self) -> Option<usize> {
        self.index
    }

    ///  The optional alpha cutoff value of the material.
    pub fn alpha_cutoff(&self) -> Option<f32> {
        self.json.alpha_cutoff.map(|value| value.0)
    }

    /// The alpha rendering mode of the material.  The material's alpha rendering
    /// mode enumeration specifying the interpretation of the alpha value of the main
    /// factor and texture.
    ///
    /// * In `Opaque` mode (default) the alpha value is ignored
    ///   and the rendered output is fully opaque.
    /// * In `Mask` mode, the rendered
    ///   output is either fully opaque or fully transparent depending on the alpha
    ///   value and the specified alpha cutoff value.
    /// * In `Blend` mode, the alpha value is used to composite the source and
    ///   destination areas and the rendered output is combined with the background
    ///   using the normal painting operation (i.e. the Porter and Duff over
    ///   operator).
    pub fn alpha_mode(&self) -> AlphaMode {
        self.json.alpha_mode.unwrap()
    }

    /// Specifies whether the material is double-sided.
    ///
    /// * When this value is false, back-face culling is enabled.
    /// * When this value is true, back-face culling is disabled and double sided
    ///   lighting is enabled.  The back-face must have its normals reversed before
    ///   the lighting equation is evaluated.
    pub fn double_sided(&self) -> bool {
        self.json.double_sided
    }

    /// Optional user-defined name for this object.
    #[cfg(feature = "names")]
    #[cfg_attr(docsrs, doc(cfg(feature = "names")))]
    pub fn name(&self) -> Option<&'a str> {
        self.json.name.as_deref()
    }

    /// Parameter values that define the metallic-roughness material model from
    /// Physically-Based Rendering (PBR) methodology.
    pub fn pbr_metallic_roughness(&self) -> PbrMetallicRoughness<'a> {
        PbrMetallicRoughness::new(self.document, &self.json.pbr_metallic_roughness)
    }

    /// Returns extension data unknown to this crate version.
    #[cfg(feature = "extensions")]
    #[cfg_attr(docsrs, doc(cfg(feature = "extensions")))]
    pub fn extensions(&self) -> Option<&Map<String, Value>> {
        let ext = self.json.extensions.as_ref()?;
        Some(&ext.others)
    }

    /// Get the value of an extension based on the name of the extension
    #[cfg(feature = "extensions")]
    #[cfg_attr(docsrs, doc(cfg(feature = "extensions")))]
    pub fn extension_value(&self, key: &str) -> Option<&Value> {
        let ext = self.json.extensions.as_ref()?;
        ext.others.get(key)
    }

    /// Parameter values that define the specular-glossiness material model from
    /// Physically-Based Rendering (PBR) methodology.
    #[cfg(feature = "KHR_materials_pbrSpecularGlossiness")]
    #[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_pbrSpecularGlossiness")))]
    pub fn pbr_specular_glossiness(&self) -> Option<PbrSpecularGlossiness<'a>> {
        self.json
            .extensions
            .as_ref()?
            .pbr_specular_glossiness
            .as_ref()
            .map(|x| PbrSpecularGlossiness::new(self.document, x))
    }

    /// Parameter values that define the transmission of light through the material
    #[cfg(feature = "KHR_materials_transmission")]
    #[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_transmission")))]
    pub fn transmission(&self) -> Option<Transmission<'a>> {
        self.json
            .extensions
            .as_ref()?
            .transmission
            .as_ref()
            .map(|x| Transmission::new(self.document, x))
    }

    /// Parameter values that define the index of refraction of the material
    #[cfg(feature = "KHR_materials_ior")]
    #[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_ior")))]
    pub fn ior(&self) -> Option<f32> {
        self.json.extensions.as_ref()?.ior.as_ref().map(|x| x.ior.0)
    }

    /// Parameter value that adjusts the strength of emissive material properties
    #[cfg(feature = "KHR_materials_emissive_strength")]
    #[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_emissive_strength")))]
    pub fn emissive_strength(&self) -> Option<f32> {
        self.json
            .extensions
            .as_ref()?
            .emissive_strength
            .as_ref()
            .map(|x| x.emissive_strength.0)
    }

    /// Parameter values that define a volume for the transmission of light through the material
    #[cfg(feature = "KHR_materials_volume")]
    #[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_volume")))]
    pub fn volume(&self) -> Option<Volume<'a>> {
        self.json
            .extensions
            .as_ref()?
            .volume
            .as_ref()
            .map(|x| Volume::new(self.document, x))
    }

    /// Parameter values that define the strength and colour of the specular reflection of the material
    #[cfg(feature = "KHR_materials_specular")]
    #[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_specular")))]
    pub fn specular(&self) -> Option<Specular<'a>> {
        self.json
            .extensions
            .as_ref()?
            .specular
            .as_ref()
            .map(|x| Specular::new(self.document, x))
    }

    /// A tangent space normal map.
    ///
    /// The texture contains RGB components in linear space. Each texel represents
    /// the XYZ components of a normal vector in tangent space.
    ///
    /// * Red [0 to 255] maps to X [-1 to 1].
    /// * Green [0 to 255] maps to Y [-1 to 1].
    /// * Blue [128 to 255] maps to Z [1/255 to 1].
    ///
    /// The normal vectors use OpenGL conventions where +X is right, +Y is up, and
    /// +Z points toward the viewer.
    pub fn normal_texture(&self) -> Option<NormalTexture<'a>> {
        self.json.normal_texture.as_ref().map(|json| {
            let texture = self.document.textures().nth(json.index.value()).unwrap();
            NormalTexture::new(texture, json)
        })
    }

    /// The occlusion map texture.
    ///
    /// The occlusion values are sampled from the R channel. Higher values indicate
    /// areas that should receive full indirect lighting and lower values indicate
    /// no indirect lighting. These values are linear.
    ///
    /// If other channels are present (GBA), they are ignored for occlusion
    /// calculations.
    pub fn occlusion_texture(&self) -> Option<OcclusionTexture<'a>> {
        self.json.occlusion_texture.as_ref().map(|json| {
            let texture = self.document.textures().nth(json.index.value()).unwrap();
            OcclusionTexture::new(texture, json)
        })
    }

    /// The emissive map texture.
    ///
    /// The emissive map controls the color and intensity of the light being
    /// emitted by the material.
    ///
    /// This texture contains RGB components in sRGB color space. If a fourth
    /// component (A) is present, it is ignored.
    pub fn emissive_texture(&self) -> Option<texture::Info<'a>> {
        self.json.emissive_texture.as_ref().map(|json| {
            let texture = self.document.textures().nth(json.index.value()).unwrap();
            texture::Info::new(texture, json)
        })
    }

    /// The emissive color of the material.
    ///
    /// The default value is `[0.0, 0.0, 0.0]`.
    pub fn emissive_factor(&self) -> [f32; 3] {
        self.json.emissive_factor.0
    }

    /// Specifies whether the material is unlit.
    ///
    /// Returns `true` if the [`KHR_materials_unlit`] property was specified, in which
    /// case the renderer should prefer to ignore all PBR values except `baseColor`.
    ///
    /// [`KHR_materials_unlit`]: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_unlit#overview
    #[cfg(feature = "KHR_materials_unlit")]
    #[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_unlit")))]
    pub fn unlit(&self) -> bool {
        self.json
            .extensions
            .as_ref()
            .map_or(false, |extensions| extensions.unlit.is_some())
    }

    /// Optional application specific data.
    pub fn extras(&self) -> &'a json::Extras {
        &self.json.extras
    }
}

/// A set of parameter values that are used to define the metallic-roughness
/// material model from Physically-Based Rendering (PBR) methodology.
pub struct PbrMetallicRoughness<'a> {
    /// The parent `Document` struct.
    document: &'a Document,

    /// The corresponding JSON struct.
    json: &'a json::material::PbrMetallicRoughness,
}

impl<'a> PbrMetallicRoughness<'a> {
    /// Constructs `PbrMetallicRoughness`.
    pub(crate) fn new(
        document: &'a Document,
        json: &'a json::material::PbrMetallicRoughness,
    ) -> Self {
        Self { document, json }
    }

    /// Returns the material's base color factor.
    ///
    /// The default value is `[1.0, 1.0, 1.0, 1.0]`.
    pub fn base_color_factor(&self) -> [f32; 4] {
        self.json.base_color_factor.0
    }

    /// Returns the base color texture. The texture contains RGB(A) components
    /// in sRGB color space.
    pub fn base_color_texture(&self) -> Option<texture::Info<'a>> {
        self.json.base_color_texture.as_ref().map(|json| {
            let texture = self.document.textures().nth(json.index.value()).unwrap();
            texture::Info::new(texture, json)
        })
    }

    /// Returns the metalness factor of the material.
    ///
    /// The default value is `1.0`.
    pub fn metallic_factor(&self) -> f32 {
        self.json.metallic_factor.0
    }

    /// Returns the roughness factor of the material.
    ///
    /// * A value of 1.0 means the material is completely rough.
    /// * A value of 0.0 means the material is completely smooth.
    ///
    /// The default value is `1.0`.
    pub fn roughness_factor(&self) -> f32 {
        self.json.roughness_factor.0
    }

    /// The metallic-roughness texture.
    ///
    /// The metalness values are sampled from the B channel.
    /// The roughness values are sampled from the G channel.
    /// These values are linear. If other channels are present (R or A),
    /// they are ignored for metallic-roughness calculations.
    pub fn metallic_roughness_texture(&self) -> Option<texture::Info<'a>> {
        self.json.metallic_roughness_texture.as_ref().map(|json| {
            let texture = self.document.textures().nth(json.index.value()).unwrap();
            texture::Info::new(texture, json)
        })
    }

    /// Returns extension data unknown to this crate version.
    #[cfg(feature = "extensions")]
    #[cfg_attr(docsrs, doc(cfg(feature = "extensions")))]
    pub fn extensions(&self) -> Option<&Map<String, Value>> {
        let ext = self.json.extensions.as_ref()?;
        Some(&ext.others)
    }

    /// Get the value of an extension based on the name of the extension
    #[cfg(feature = "extensions")]
    #[cfg_attr(docsrs, doc(cfg(feature = "extensions")))]
    pub fn extension_value(&self, key: &str) -> Option<&Value> {
        let ext = self.json.extensions.as_ref()?;
        ext.others.get(key)
    }

    /// Optional application specific data.
    pub fn extras(&self) -> &'a json::Extras {
        &self.json.extras
    }
}

/// A set of parameter values that are used to define the transmissions
/// factor of the material
#[cfg(feature = "KHR_materials_transmission")]
#[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_transmission")))]
pub struct Transmission<'a> {
    /// The parent `Document` struct.
    document: &'a Document,

    /// The corresponding JSON struct.
    json: &'a json::extensions::material::Transmission,
}

#[cfg(feature = "KHR_materials_transmission")]
#[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_transmission")))]
impl<'a> Transmission<'a> {
    /// Constructs `Ior`.
    pub(crate) fn new(
        document: &'a Document,
        json: &'a json::extensions::material::Transmission,
    ) -> Self {
        Self { document, json }
    }

    /// Returns the material's transmission factor.
    ///
    /// The default value is `0.0`.
    pub fn transmission_factor(&self) -> f32 {
        self.json.transmission_factor.0
    }

    /// Returns the transmission texture.
    pub fn transmission_texture(&self) -> Option<texture::Info<'a>> {
        self.json.transmission_texture.as_ref().map(|json| {
            let texture = self.document.textures().nth(json.index.value()).unwrap();
            texture::Info::new(texture, json)
        })
    }

    /// Optional application specific data.
    pub fn extras(&self) -> &'a json::Extras {
        &self.json.extras
    }
}

/// Parameter values that define a volume for the transmission of light through the material
#[cfg(feature = "KHR_materials_volume")]
#[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_volume")))]
pub struct Volume<'a> {
    /// The parent `Document` struct.
    document: &'a Document,

    /// The corresponding JSON struct.
    json: &'a json::extensions::material::Volume,
}

#[cfg(feature = "KHR_materials_volume")]
#[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_volume")))]
impl<'a> Volume<'a> {
    /// Constructs `Volume`.
    pub(crate) fn new(
        document: &'a Document,
        json: &'a json::extensions::material::Volume,
    ) -> Self {
        Self { document, json }
    }

    /// The thickness of the volume beneath the surface. The value is
    /// given in the coordinate space of the mesh. If the value is 0
    /// the material is thin-walled. Otherwise the material is a
    /// volume boundary. The `doubleSided` property has no effect on
    /// volume boundaries. Range is [0, +inf).
    pub fn thickness_factor(&self) -> f32 {
        self.json.thickness_factor.0
    }

    /// A texture that defines the thickness, stored in the G channel.
    /// This will be multiplied by `thickness_factor`. Range is [0, 1].
    pub fn thickness_texture(&self) -> Option<texture::Info<'a>> {
        self.json.thickness_texture.as_ref().map(|json| {
            let texture = self.document.textures().nth(json.index.value()).unwrap();
            texture::Info::new(texture, json)
        })
    }

    /// Density of the medium given as the average distance that light
    /// travels in the medium before interacting with a particle. The
    /// value is given in world space. Range is (0, +inf).
    pub fn attenuation_distance(&self) -> f32 {
        self.json.attenuation_distance.0
    }

    /// The color that white light turns into due to absorption when
    /// reaching the attenuation distance.
    pub fn attenuation_color(&self) -> [f32; 3] {
        self.json.attenuation_color.0
    }

    /// Optional application specific data.
    pub fn extras(&self) -> &'a json::Extras {
        &self.json.extras
    }
}

/// Parameter values that define the strength and colour of the specular reflection of the material
#[cfg(feature = "KHR_materials_specular")]
#[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_specular")))]
pub struct Specular<'a> {
    /// The parent `Document` struct.
    document: &'a Document,

    /// The corresponding JSON struct.
    json: &'a json::extensions::material::Specular,
}

#[cfg(feature = "KHR_materials_specular")]
#[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_specular")))]
impl<'a> Specular<'a> {
    /// Constructs `Volume`.
    pub(crate) fn new(
        document: &'a Document,
        json: &'a json::extensions::material::Specular,
    ) -> Self {
        Self { document, json }
    }

    /// The strength of the specular reflection.
    pub fn specular_factor(&self) -> f32 {
        self.json.specular_factor.0
    }

    /// A texture that defines the strength of the specular reflection,
    /// stored in the alpha (`A`) channel. This will be multiplied by
    /// `specular_factor`.
    pub fn specular_texture(&self) -> Option<texture::Info<'a>> {
        self.json.specular_texture.as_ref().map(|json| {
            let texture = self.document.textures().nth(json.index.value()).unwrap();
            texture::Info::new(texture, json)
        })
    }

    /// The F0 color of the specular reflection (linear RGB).
    pub fn specular_color_factor(&self) -> [f32; 3] {
        self.json.specular_color_factor.0
    }

    /// A texture that defines the F0 color of the specular reflection,
    /// stored in the `RGB` channels and encoded in sRGB. This texture
    /// will be multiplied by `specular_color_factor`.
    pub fn specular_color_texture(&self) -> Option<texture::Info<'a>> {
        self.json.specular_color_texture.as_ref().map(|json| {
            let texture = self.document.textures().nth(json.index.value()).unwrap();
            texture::Info::new(texture, json)
        })
    }

    /// Optional application specific data.
    pub fn extras(&self) -> &'a json::Extras {
        &self.json.extras
    }
}

/// A set of parameter values that are used to define the specular-glossiness
/// material model from Physically-Based Rendering (PBR) methodology.
#[cfg(feature = "KHR_materials_pbrSpecularGlossiness")]
#[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_pbrSpecularGlossiness")))]
pub struct PbrSpecularGlossiness<'a> {
    /// The parent `Document` struct.
    document: &'a Document,

    /// The corresponding JSON struct.
    json: &'a json::extensions::material::PbrSpecularGlossiness,
}

#[cfg(feature = "KHR_materials_pbrSpecularGlossiness")]
#[cfg_attr(docsrs, doc(cfg(feature = "KHR_materials_pbrSpecularGlossiness")))]
impl<'a> PbrSpecularGlossiness<'a> {
    /// Constructs `PbrSpecularGlossiness`.
    pub(crate) fn new(
        document: &'a Document,
        json: &'a json::extensions::material::PbrSpecularGlossiness,
    ) -> Self {
        Self { document, json }
    }

    /// Returns the material's base color factor.
    ///
    /// The default value is `[1.0, 1.0, 1.0, 1.0]`.
    pub fn diffuse_factor(&self) -> [f32; 4] {
        self.json.diffuse_factor.0
    }

    /// Returns the base color texture.
    pub fn diffuse_texture(&self) -> Option<texture::Info<'a>> {
        self.json.diffuse_texture.as_ref().map(|json| {
            let texture = self.document.textures().nth(json.index.value()).unwrap();
            texture::Info::new(texture, json)
        })
    }

    /// Returns the specular factor of the material.
    ///
    /// The default value is `[1.0, 1.0, 1.0]`.
    pub fn specular_factor(&self) -> [f32; 3] {
        self.json.specular_factor.0
    }

    /// Returns the glossiness factor of the material.
    ///
    /// A value of 1.0 means the material has full glossiness or is perfectly
    /// smooth. A value of 0.0 means the material has no glossiness or is
    /// completely rough. This value is linear.
    ///
    /// The default value is `1.0`.
    pub fn glossiness_factor(&self) -> f32 {
        self.json.glossiness_factor.0
    }

    /// The specular-glossiness texture.
    ///
    /// A RGBA texture, containing the specular color of the material (RGB
    /// components) and its glossiness (A component). The color values are in
    /// sRGB space.
    pub fn specular_glossiness_texture(&self) -> Option<texture::Info<'a>> {
        self.json.specular_glossiness_texture.as_ref().map(|json| {
            let texture = self.document.textures().nth(json.index.value()).unwrap();
            texture::Info::new(texture, json)
        })
    }

    /// Optional application specific data.
    pub fn extras(&self) -> &'a json::Extras {
        &self.json.extras
    }
}

/// Defines the normal texture of a material.
pub struct NormalTexture<'a> {
    /// The parent `Texture` struct.
    texture: texture::Texture<'a>,

    /// The corresponding JSON struct.
    json: &'a json::material::NormalTexture,
}

impl<'a> NormalTexture<'a> {
    /// Constructs a `NormalTexture`.
    pub(crate) fn new(
        texture: texture::Texture<'a>,
        json: &'a json::material::NormalTexture,
    ) -> Self {
        Self { texture, json }
    }

    /// Returns the scalar multiplier applied to each normal vector of the texture.
    pub fn scale(&self) -> f32 {
        self.json.scale
    }

    /// The set index of the texture's `TEXCOORD` attribute.
    pub fn tex_coord(&self) -> u32 {
        self.json.tex_coord
    }

    /// Returns the referenced texture.
    pub fn texture(&self) -> texture::Texture<'a> {
        self.texture.clone()
    }

    /// Returns extension data unknown to this crate version.
    #[cfg(feature = "extensions")]
    #[cfg_attr(docsrs, doc(cfg(feature = "extensions")))]
    pub fn extensions(&self) -> Option<&Map<String, Value>> {
        let ext = self.json.extensions.as_ref()?;
        Some(&ext.others)
    }

    /// Get the value of an extension based on the name of the extension
    #[cfg(feature = "extensions")]
    #[cfg_attr(docsrs, doc(cfg(feature = "extensions")))]
    pub fn extension_value(&self, key: &str) -> Option<&Value> {
        let ext = self.json.extensions.as_ref()?;
        ext.others.get(key)
    }

    /// Optional application specific data.
    pub fn extras(&self) -> &'a json::Extras {
        &self.json.extras
    }
}

/// Defines the occlusion texture of a material.
pub struct OcclusionTexture<'a> {
    /// The parent `Texture` struct.
    texture: texture::Texture<'a>,

    /// The corresponding JSON struct.
    json: &'a json::material::OcclusionTexture,
}

impl<'a> OcclusionTexture<'a> {
    /// Constructs a `OcclusionTexture`.
    pub(crate) fn new(
        texture: texture::Texture<'a>,
        json: &'a json::material::OcclusionTexture,
    ) -> Self {
        Self { texture, json }
    }

    /// Returns the scalar multiplier controlling the amount of occlusion applied.
    pub fn strength(&self) -> f32 {
        self.json.strength.0
    }

    /// Returns the set index of the texture's `TEXCOORD` attribute.
    pub fn tex_coord(&self) -> u32 {
        self.json.tex_coord
    }

    /// Returns the referenced texture.
    pub fn texture(&self) -> texture::Texture<'a> {
        self.texture.clone()
    }

    /// Returns extension data unknown to this crate version.
    #[cfg(feature = "extensions")]
    #[cfg_attr(docsrs, doc(cfg(feature = "extensions")))]
    pub fn extensions(&self) -> Option<&Map<String, Value>> {
        let ext = self.json.extensions.as_ref()?;
        Some(&ext.others)
    }

    /// Get the value of an extension based on the name of the extension
    #[cfg(feature = "extensions")]
    #[cfg_attr(docsrs, doc(cfg(feature = "extensions")))]
    pub fn extension_value(&self, key: &str) -> Option<&Value> {
        let ext = self.json.extensions.as_ref()?;
        ext.others.get(key)
    }

    /// Optional application specific data.
    pub fn extras(&self) -> &'a json::Extras {
        &self.json.extras
    }
}

impl<'a> AsRef<texture::Texture<'a>> for NormalTexture<'a> {
    fn as_ref(&self) -> &texture::Texture<'a> {
        &self.texture
    }
}

impl<'a> AsRef<texture::Texture<'a>> for OcclusionTexture<'a> {
    fn as_ref(&self) -> &texture::Texture<'a> {
        &self.texture
    }
}