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
//! The type of film or sensor in a camera has a dramatic effect on
//! the way that incident light is transformed into colors in an
//! image. In **pbrt**, the **Film** class models the sensing device
//! in the simulated camera. After the radiance is found for each
//! camera ray, the **Film** implementation determines the sample's
//! contribution to the pixel around the point on the film plane where
//! the camera ray began and updates its representation of the
//! image. When the main rendering loop exits, the **Film** writes the
//! final image to file.
//!

// std
use std::ops::{DerefMut, Index};
use std::path::Path;
use std::sync::{Arc, RwLock, RwLockWriteGuard};

// others
#[cfg(feature = "openexr")]
use openexr::{FrameBuffer, Header, PixelType, ScanlineOutputFile};
use smallvec::SmallVec;
// pbrt
use crate::core::filter::Filter;
use crate::core::geometry::{
    bnd2_intersect_bnd2i, pnt2_ceil, pnt2_floor, pnt2_inside_exclusivei, pnt2_max_pnt2i,
    pnt2_min_pnt2i,
};
use crate::core::geometry::{Bounds2f, Bounds2i, Point2f, Point2i, Vector2f};
use crate::core::paramset::ParamSet;
use crate::core::pbrt::{clamp_t, gamma_correct};
use crate::core::pbrt::{Float, Spectrum};
use crate::core::spectrum::xyz_to_rgb;

// see film.h

const FILTER_TABLE_WIDTH: usize = 16;

#[derive(Debug, Clone)]
pub struct Pixel {
    pub(crate) xyz: [Float; 3],
    pub(crate) filter_weight_sum: Float,
    splat_xyz: [Float; 3],
    // pad: Float,
}

impl Default for Pixel {
    fn default() -> Self {
        Pixel {
            xyz: [0.0 as Float; 3],
            filter_weight_sum: 0.0 as Float,
            splat_xyz: [Float::default(), Float::default(), Float::default()],
            // pad: 0.0 as Float,
        }
    }
}

#[derive(Debug, Default, Copy, Clone)]
pub struct FilmTilePixel {
    contrib_sum: Spectrum,
    filter_weight_sum: Float,
}

pub struct FilmTile<'a> {
    pub pixel_bounds: Bounds2i,
    filter_radius: Vector2f,
    inv_filter_radius: Vector2f,
    filter_table: &'a [Float; FILTER_TABLE_WIDTH * FILTER_TABLE_WIDTH],
    filter_table_size: usize,
    pixels: Vec<FilmTilePixel>,
    max_sample_luminance: Float,
}

impl<'a> FilmTile<'a> {
    pub fn new(
        pixel_bounds: Bounds2i,
        filter_radius: Vector2f,
        filter_table: &'a [Float; FILTER_TABLE_WIDTH * FILTER_TABLE_WIDTH],
        filter_table_size: usize,
        max_sample_luminance: Float,
    ) -> Self {
        FilmTile {
            pixel_bounds,
            filter_radius,
            inv_filter_radius: Vector2f {
                x: 1.0 / filter_radius.x,
                y: 1.0 / filter_radius.y,
            },
            filter_table,
            filter_table_size,
            // TODO: pixels = std::vector<FilmTilePixel>(std::max(0, pixelBounds.Area()));
            pixels: vec![FilmTilePixel::default(); pixel_bounds.area() as usize],
            max_sample_luminance,
        }
    }
    pub fn add_sample(&mut self, p_film: Point2f, l: &mut Spectrum, sample_weight: Float) {
        // TODO: ProfilePhase _(Prof::AddFilmSample);
        if l.y() > self.max_sample_luminance {
            *l *= Spectrum::new(self.max_sample_luminance / l.y());
        }
        // compute sample's raster bounds
        let p_film_discrete: Point2f = p_film - Vector2f { x: 0.5, y: 0.5 };
        let p0f: Point2f = pnt2_ceil(p_film_discrete - self.filter_radius);
        let mut p0: Point2i = Point2i {
            x: p0f.x as i32,
            y: p0f.y as i32,
        };
        let p1f: Point2f = pnt2_floor(p_film_discrete + self.filter_radius);
        let mut p1: Point2i = Point2i {
            x: p1f.x as i32 + 1,
            y: p1f.y as i32 + 1,
        };
        p0 = pnt2_max_pnt2i(p0, self.pixel_bounds.p_min);
        p1 = pnt2_min_pnt2i(p1, self.pixel_bounds.p_max);

        // loop over filter support and add sample to pixel arrays

        // precompute $x$ and $y$ filter table offsets
        let mut ifx: SmallVec<[usize; 16]> = SmallVec::with_capacity(p1.x as usize - p0.x as usize);
        for x in p0.x..p1.x {
            let fx: Float = ((x as Float - p_film_discrete.x)
                * self.inv_filter_radius.x
                * self.filter_table_size as Float)
                .abs();
            ifx.push(fx.floor().min(self.filter_table_size as Float - 1.0) as usize);
        }
        let mut ify: SmallVec<[usize; 16]> = SmallVec::with_capacity(p1.y as usize - p0.y as usize);
        for y in p0.y..p1.y {
            let fy: Float = ((y as Float - p_film_discrete.y)
                * self.inv_filter_radius.y
                * self.filter_table_size as Float)
                .abs();
            ify.push(fy.floor().min(self.filter_table_size as Float - 1.0) as usize);
        }
        for y in p0.y..p1.y {
            for x in p0.x..p1.x {
                // evaluate filter value at $(x,y)$ pixel
                let offset: usize =
                    ify[(y - p0.y) as usize] * self.filter_table_size + ifx[(x - p0.x) as usize];
                let filter_weight: Float = self.filter_table[offset];
                // update pixel values with filtered sample contribution
                let idx = self.get_pixel_index(x, y);
                let pixel = &mut self.pixels[idx];
                pixel.contrib_sum +=
                    *l * Spectrum::new(sample_weight) * Spectrum::new(filter_weight);
                pixel.filter_weight_sum += filter_weight;
            }
        }
    }
    fn get_pixel_index(&self, x: i32, y: i32) -> usize {
        let width: i32 = self.pixel_bounds.p_max.x - self.pixel_bounds.p_min.x;
        let pidx = (y - self.pixel_bounds.p_min.y) * width + (x - self.pixel_bounds.p_min.x);
        pidx as usize
    }
}

pub struct Film {
    // Film Public Data
    /// The overall resolution of the image in pixels
    pub full_resolution: Point2i,
    /// The length of the diagonal of the film's physical area (specified in mm, stored in meters)
    pub diagonal: Float,
    /// A filter function
    pub filter: Box<Filter>,
    /// The filename of the output image
    pub filename: String,
    /// A crop window that may specify a subset of the image to render
    pub cropped_pixel_bounds: Bounds2i,

    // Film Private Data
    pub pixels: RwLock<Vec<Pixel>>,
    filter_table: [Float; FILTER_TABLE_WIDTH * FILTER_TABLE_WIDTH],
    scale: Float,
    max_sample_luminance: Float,
}

impl Film {
    pub fn new(
        resolution: Point2i,
        crop_window: Bounds2f,
        filter: Box<Filter>,
        diagonal: Float,
        filename: String,
        scale: Float,
        max_sample_luminance: Float,
    ) -> Self {
        let cropped_pixel_bounds: Bounds2i = Bounds2i {
            p_min: Point2i {
                x: (resolution.x as Float * crop_window.p_min.x).ceil() as i32,
                y: (resolution.y as Float * crop_window.p_min.y).ceil() as i32,
            },
            p_max: Point2i {
                x: (resolution.x as Float * crop_window.p_max.x).ceil() as i32,
                y: (resolution.y as Float * crop_window.p_max.y).ceil() as i32,
            },
        };
        // allocate film image storage
        // let pixels: Vec<Pixel> = vec![Pixel::default(); cropped_pixel_bounds.area() as usize];
        // precompute filter weight table
        let mut filter_table: [Float; FILTER_TABLE_WIDTH * FILTER_TABLE_WIDTH] =
            [0.0; FILTER_TABLE_WIDTH * FILTER_TABLE_WIDTH];
        let mut offset: usize = 0;
        let filter_radius: Vector2f = filter.get_radius();
        for y in 0..FILTER_TABLE_WIDTH {
            for x in 0..FILTER_TABLE_WIDTH {
                let p: Point2f = Point2f {
                    x: (x as Float + 0.5) * filter_radius.x / FILTER_TABLE_WIDTH as Float,
                    y: (y as Float + 0.5) * filter_radius.y / FILTER_TABLE_WIDTH as Float,
                };
                filter_table[offset] = filter.evaluate(p);
                offset += 1;
            }
        }
        Film {
            full_resolution: resolution,
            diagonal: diagonal * 0.001,
            filter,
            filename,
            cropped_pixel_bounds,
            pixels: RwLock::new(vec![Pixel::default(); cropped_pixel_bounds.area() as usize]),
            filter_table,
            scale,
            max_sample_luminance,
        }
    }
    pub fn create(params: &ParamSet, filter: Box<Filter>, crop_window: &Bounds2f) -> Arc<Film> {
        let filename: String = params.find_one_string("filename", String::new());
        let xres: i32 = params.find_one_int("xresolution", 1280);
        let yres: i32 = params.find_one_int("yresolution", 720);
        let resolution: Point2i = Point2i { x: xres, y: yres };
        // TODO: if (PbrtOptions.quickRender) xres = std::max(1, xres / 4);
        // TODO: if (PbrtOptions.quickRender) yres = std::max(1, yres / 4);
        let mut crop: Bounds2f = Bounds2f {
            p_min: Point2f { x: 0.0, y: 0.0 },
            p_max: Point2f { x: 1.0, y: 1.0 },
        };
        let cr: Vec<Float> = params.find_float("cropwindow");
        if cr.len() == 4 {
            crop.p_min.x = clamp_t(cr[0].min(cr[1]), 0.0, 1.0);
            crop.p_max.x = clamp_t(cr[0].max(cr[1]), 0.0, 1.0);
            crop.p_min.y = clamp_t(cr[2].min(cr[3]), 0.0, 1.0);
            crop.p_max.y = clamp_t(cr[2].max(cr[3]), 0.0, 1.0);
        } else if !cr.is_empty() {
            panic!(
                "{:?} values supplied for \"cropwindow\". Expected 4.",
                cr.len()
            );
        } else {
            crop = *crop_window;
        }
        let scale: Float = params.find_one_float("scale", 1.0);
        let diagonal: Float = params.find_one_float("diagonal", 35.0);
        let max_sample_luminance: Float =
            params.find_one_float("maxsampleluminance", std::f32::INFINITY);
        Arc::new(Film::new(
            resolution,
            crop,
            filter,
            diagonal,
            filename,
            scale,
            max_sample_luminance,
        ))
    }
    pub fn get_cropped_pixel_bounds(&self) -> Bounds2i {
        self.cropped_pixel_bounds
    }
    pub fn get_sample_bounds(&self) -> Bounds2i {
        let f: Point2f = pnt2_floor(
            Point2f {
                x: self.cropped_pixel_bounds.p_min.x as Float,
                y: self.cropped_pixel_bounds.p_min.y as Float,
            } + Vector2f { x: 0.5, y: 0.5 }
                - self.filter.get_radius(),
        );
        let c: Point2f = pnt2_ceil(
            Point2f {
                x: self.cropped_pixel_bounds.p_max.x as Float,
                y: self.cropped_pixel_bounds.p_max.y as Float,
            } - Vector2f { x: 0.5, y: 0.5 }
                + self.filter.get_radius(),
        );
        let float_bounds: Bounds2f = Bounds2f { p_min: f, p_max: c };
        Bounds2i {
            p_min: Point2i {
                x: float_bounds.p_min.x as i32,
                y: float_bounds.p_min.y as i32,
            },
            p_max: Point2i {
                x: float_bounds.p_max.x as i32,
                y: float_bounds.p_max.y as i32,
            },
        }
    }
    pub fn get_physical_extent(&self) -> Bounds2f {
        let aspect: Float = self.full_resolution.y as Float / self.full_resolution.x as Float;
        let x: Float = (self.diagonal * self.diagonal / (1.0 as Float + aspect * aspect)).sqrt();
        let y: Float = aspect * x;
        Bounds2f {
            p_min: Point2f {
                x: -x / 2.0 as Float,
                y: -y / 2.0 as Float,
            },
            p_max: Point2f {
                x: x / 2.0 as Float,
                y: y / 2.0 as Float,
            },
        }
    }
    pub fn get_film_tile(&self, sample_bounds: &Bounds2i) -> FilmTile {
        // bound image pixels that samples in _sample_bounds_ contribute to
        let half_pixel: Vector2f = Vector2f { x: 0.5, y: 0.5 };
        let float_bounds: Bounds2f = Bounds2f {
            p_min: Point2f {
                x: sample_bounds.p_min.x as Float,
                y: sample_bounds.p_min.y as Float,
            },
            p_max: Point2f {
                x: sample_bounds.p_max.x as Float,
                y: sample_bounds.p_max.y as Float,
            },
        };
        let p_min: Point2f = float_bounds.p_min - half_pixel - self.filter.get_radius();
        let p0: Point2i = Point2i {
            x: p_min.x.ceil() as i32,
            y: p_min.y.ceil() as i32,
        };
        let p_max: Point2f = float_bounds.p_max - half_pixel + self.filter.get_radius();
        let p1: Point2i = Point2i {
            x: p_max.x.floor() as i32,
            y: p_max.y.floor() as i32,
        } + Point2i { x: 1, y: 1 };
        let tile_pixel_bounds: Bounds2i = bnd2_intersect_bnd2i(
            &Bounds2i {
                p_min: p0,
                p_max: p1,
            },
            &self.cropped_pixel_bounds,
        );
        FilmTile::new(
            tile_pixel_bounds,
            self.filter.get_radius(),
            &self.filter_table,
            FILTER_TABLE_WIDTH,
            self.max_sample_luminance,
        )
    }
    pub fn merge_film_tile(&self, tile: &FilmTile) {
        // TODO: ProfilePhase p(Prof::MergeFilmTile);
        // println!("Merging film tile {:?}", tile.pixel_bounds);
        // TODO: std::lock_guard<std::mutex> lock(mutex);
        for pixel in &tile.pixel_bounds {
            // merge _pixel_ into _Film::pixels_
            let idx = tile.get_pixel_index(pixel.x, pixel.y);
            let tile_pixel = &tile.pixels[idx];
            // START let mut merge_pixel: &mut Pixel = self.get_pixel_mut(pixel);
            assert!(pnt2_inside_exclusivei(pixel, &self.cropped_pixel_bounds));
            let width: i32 = self.cropped_pixel_bounds.p_max.x - self.cropped_pixel_bounds.p_min.x;
            let offset: i32 = (pixel.x - self.cropped_pixel_bounds.p_min.x)
                + (pixel.y - self.cropped_pixel_bounds.p_min.y) * width;
            let mut pixels_write = self.pixels.write().unwrap();
            let merge_pixel = &mut pixels_write[offset as usize];
            // END let mut merge_pixel: &mut Pixel = self.get_pixel_mut(pixel);
            let mut xyz: [Float; 3] = [0.0; 3];
            tile_pixel.contrib_sum.to_xyz(&mut xyz);
            for (i, item) in xyz.iter().enumerate() {
                merge_pixel.xyz[i] += item;
            }
            merge_pixel.filter_weight_sum += tile_pixel.filter_weight_sum;
            // write pixel back
            // pixels_write[offset as usize] = *merge_pixel;
        }
    }
    pub fn set_image(&self, img: &[Spectrum]) {
        let n_pixels: i32 = self.cropped_pixel_bounds.area();
        let mut pixels_write = self.pixels.write().unwrap();
        for i in 0..n_pixels as usize {
            let merge_pixel = &mut pixels_write[i];
            let mut xyz: [Float; 3] = [0.0; 3];
            img[i].to_xyz(&mut xyz);
            for (i, item) in xyz.iter().enumerate() {
                merge_pixel.xyz[i] = *item;
            }
            merge_pixel.filter_weight_sum = 1.0 as Float;
            merge_pixel.splat_xyz[0] = 0.0;
            merge_pixel.splat_xyz[1] = 0.0;
            merge_pixel.splat_xyz[2] = 0.0;
        }
    }
    pub fn add_splat(&self, p: Point2f, v: &Spectrum) {
        let mut v: Spectrum = *v;
        // TODO: ProfilePhase pp(Prof::SplatFilm);
        if v.has_nans() {
            println!(
                "ERROR: Ignoring splatted spectrum with NaN values at ({:?}, {:?})",
                p.x, p.y
            );
            return;
        } else if v.y() < 0.0 as Float {
            println!(
                "ERROR: Ignoring splatted spectrum with negative luminance {:?} at ({:?}, {:?})",
                v.y(),
                p.x,
                p.y
            );
            return;
        } else if v.y().is_infinite() {
            println!(
                "ERROR: Ignoring splatted spectrum with infinite luminance at ({:?}, {:?})",
                p.x, p.y
            );
            return;
        }

        let pi: Point2i = Point2i {
            x: p.x as i32,
            y: p.y as i32,
        };
        if !pnt2_inside_exclusivei(pi, &self.cropped_pixel_bounds) {
            return;
        }
        if v.y() > self.max_sample_luminance {
            v = v * self.max_sample_luminance / v.y();
        }
        let mut xyz: [Float; 3] = [Float::default(); 3];
        v.to_xyz(&mut xyz);
        let width: i32 = self.cropped_pixel_bounds.p_max.x - self.cropped_pixel_bounds.p_min.x;
        let offset: i32 = (pi.x - self.cropped_pixel_bounds.p_min.x)
            + (pi.y - self.cropped_pixel_bounds.p_min.y) * width;
        let mut pixels_write: RwLockWriteGuard<Vec<Pixel>> = self.pixels.write().unwrap();
        let pixel_vec: &mut Vec<Pixel> = pixels_write.deref_mut();
        let pixel: &mut Pixel = &mut pixel_vec[offset as usize];

        let splat_xyz: &mut [Float; 3] = &mut pixel.splat_xyz;
        splat_xyz[0] += xyz[0];
        splat_xyz[1] += xyz[1];
        splat_xyz[2] += xyz[2];
    }
    #[cfg(not(feature = "openexr"))]
    pub fn write_image(&self, splat_scale: Float) {
        let mut rgb: Vec<Float> =
            vec![0.0 as Float; (3 * self.cropped_pixel_bounds.area()) as usize];
        let mut offset;
        for p in &self.cropped_pixel_bounds {
            // convert pixel XYZ color to RGB
            assert!(pnt2_inside_exclusivei(p, &self.cropped_pixel_bounds));
            let width: i32 = self.cropped_pixel_bounds.p_max.x - self.cropped_pixel_bounds.p_min.x;
            offset = ((p.x - self.cropped_pixel_bounds.p_min.x)
                + (p.y - self.cropped_pixel_bounds.p_min.y) * width) as usize;
            let pixel: &Pixel = &self.pixels.read().unwrap()[offset];

            let start: usize = 3 * offset;
            let mut rgb_array: [Float; 3] = [0.0 as Float; 3];
            xyz_to_rgb(&pixel.xyz, &mut rgb_array); // TODO: Use 'rgb' directly.
            rgb[start] = rgb_array[0];
            rgb[start + 1] = rgb_array[1];
            rgb[start + 2] = rgb_array[2];
            // normalize pixel with weight sum
            let filter_weight_sum: Float = pixel.filter_weight_sum;
            if filter_weight_sum != 0.0 as Float {
                let inv_wt: Float = 1.0 as Float / filter_weight_sum;
                rgb[start] = (rgb[start] * inv_wt).max(0.0 as Float);
                rgb[start + 1] = (rgb[start + 1] * inv_wt).max(0.0 as Float);
                rgb[start + 2] = (rgb[start + 2] * inv_wt).max(0.0 as Float);
            }
            // add splat value at pixel
            let mut splat_rgb: [Float; 3] = [0.0 as Float; 3];
            let pixel_splat_xyz: &[Float; 3] = &pixel.splat_xyz;
            let splat_xyz: [Float; 3] = [
                *pixel_splat_xyz.index(0),
                *pixel_splat_xyz.index(1),
                *pixel_splat_xyz.index(2),
            ];
            xyz_to_rgb(&splat_xyz, &mut splat_rgb);
            rgb[start] += splat_scale * splat_rgb[0];
            rgb[start + 1] += splat_scale * splat_rgb[1];
            rgb[start + 2] += splat_scale * splat_rgb[2];
            // scale pixel value by _scale_
            rgb[start] *= self.scale;
            rgb[start + 1] *= self.scale;
            rgb[start + 2] *= self.scale;
        }
        let filename = "pbrt.png";
        println!(
            "Writing image {:?} with bounds {:?}",
            filename, // TODO: self.filename,
            self.cropped_pixel_bounds
        );
        // TODO: pbrt::WriteImage(filename, &rgb[0], croppedPixelBounds, fullResolution);
        let mut buffer: Vec<u8> = vec![0.0 as u8; (3 * self.cropped_pixel_bounds.area()) as usize];
        // 8-bit format; apply gamma (see WriteImage(...) in imageio.cpp)
        let width: u32 =
            (self.cropped_pixel_bounds.p_max.x - self.cropped_pixel_bounds.p_min.x) as u32;
        let height: u32 =
            (self.cropped_pixel_bounds.p_max.y - self.cropped_pixel_bounds.p_min.y) as u32;
        for y in 0..height {
            for x in 0..width {
                // red
                let index: usize = (3 * (y * width + x)) as usize;
                buffer[index] = clamp_t(
                    255.0 as Float * gamma_correct(rgb[index]) + 0.5,
                    0.0 as Float,
                    255.0 as Float,
                ) as u8;
                // green
                let index: usize = (3 * (y * width + x) + 1) as usize;
                buffer[index] = clamp_t(
                    255.0 as Float * gamma_correct(rgb[index]) + 0.5,
                    0.0 as Float,
                    255.0 as Float,
                ) as u8;
                // blue
                let index: usize = (3 * (y * width + x) + 2) as usize;
                buffer[index] = clamp_t(
                    255.0 as Float * gamma_correct(rgb[index]) + 0.5,
                    0.0 as Float,
                    255.0 as Float,
                ) as u8;
            }
        }
        // write "pbrt.png" to disk
        image::save_buffer(
            Path::new("pbrt.png"),
            &buffer,
            width,
            height,
            image::ColorType::Rgb8,
        )
        .unwrap();
    }
    #[cfg(feature = "openexr")]
    pub fn write_image(&self, splat_scale: Float) {
        let mut rgb: Vec<Float> =
            vec![0.0 as Float; (3 * self.cropped_pixel_bounds.area()) as usize];
        let mut exr: Vec<(Float, Float, Float)> = // copy data for OpenEXR image
            vec![(0.0_f32, 0.0_f32, 0.0_f32); self.cropped_pixel_bounds.area() as usize];
        let mut offset;
        for p in &self.cropped_pixel_bounds {
            // convert pixel XYZ color to RGB
            assert!(pnt2_inside_exclusivei(p, &self.cropped_pixel_bounds));
            let width: i32 = self.cropped_pixel_bounds.p_max.x - self.cropped_pixel_bounds.p_min.x;
            offset = ((p.x - self.cropped_pixel_bounds.p_min.x)
                + (p.y - self.cropped_pixel_bounds.p_min.y) * width) as usize;
            let pixel: &Pixel = &self.pixels.read().unwrap()[offset];
            let start = 3 * offset;
            let mut rgb_array: [Float; 3] = [0.0 as Float; 3];
            xyz_to_rgb(&pixel.xyz, &mut rgb_array); // TODO: Use 'rgb' directly.
            rgb[start] = rgb_array[0];
            rgb[start + 1] = rgb_array[1];
            rgb[start + 2] = rgb_array[2];
            // normalize pixel with weight sum
            let filter_weight_sum: Float = pixel.filter_weight_sum;
            if filter_weight_sum != 0.0 as Float {
                let inv_wt: Float = 1.0 as Float / filter_weight_sum;
                rgb[start] = (rgb[start] * inv_wt).max(0.0 as Float);
                rgb[start + 1] = (rgb[start + 1] * inv_wt).max(0.0 as Float);
                rgb[start + 2] = (rgb[start + 2] * inv_wt).max(0.0 as Float);
            }
            // add splat value at pixel
            let mut splat_rgb: [Float; 3] = [0.0 as Float; 3];
            let pixel_splat_xyz: &[Float; 3] = &pixel.splat_xyz;
            let splat_xyz: [Float; 3] = [
                *pixel_splat_xyz.index(0),
                *pixel_splat_xyz.index(1),
                *pixel_splat_xyz.index(2),
            ];
            xyz_to_rgb(&splat_xyz, &mut splat_rgb);
            rgb[start] += splat_scale * splat_rgb[0];
            rgb[start + 1] += splat_scale * splat_rgb[1];
            rgb[start + 2] += splat_scale * splat_rgb[2];
            // scale pixel value by _scale_
            rgb[start] *= self.scale;
            rgb[start + 1] *= self.scale;
            rgb[start + 2] *= self.scale;
            // copy data for OpenEXR image
            exr[offset].0 = rgb[start];
            exr[offset].1 = rgb[start + 1];
            exr[offset].2 = rgb[start + 2];
        }
        let filename = "pbrt.png";
        println!(
            "Writing image {:?} with bounds {:?}",
            filename, // TODO: self.filename,
            self.cropped_pixel_bounds
        );
        // TODO: pbrt::WriteImage(filename, &rgb[0], croppedPixelBounds, fullResolution);
        let mut buffer: Vec<u8> = vec![0.0 as u8; (3 * self.cropped_pixel_bounds.area()) as usize];
        // 8-bit format; apply gamma (see WriteImage(...) in imageio.cpp)
        let width: u32 =
            (self.cropped_pixel_bounds.p_max.x - self.cropped_pixel_bounds.p_min.x) as u32;
        let height: u32 =
            (self.cropped_pixel_bounds.p_max.y - self.cropped_pixel_bounds.p_min.y) as u32;
        // OpenEXR
        let filename = "pbrt_rust.exr";
        println!(
            "Writing image {:?} with bounds {:?}",
            filename, // TODO: self.filename,
            self.cropped_pixel_bounds
        );
        let mut file = std::fs::File::create("pbrt_rust.exr").unwrap();
        let mut output_file = ScanlineOutputFile::new(
            &mut file,
            Header::new()
                .set_resolution(width, height)
                .add_channel("R", PixelType::FLOAT)
                .add_channel("G", PixelType::FLOAT)
                .add_channel("B", PixelType::FLOAT),
        )
        .unwrap();
        let mut fb = FrameBuffer::new(width as u32, height as u32);
        fb.insert_channels(&["R", "G", "B"], &exr);
        output_file.write_pixels(&fb).unwrap();

        // OpenEXR
        for y in 0..height {
            for x in 0..width {
                // red
                let index: usize = (3 * (y * width + x)) as usize;
                buffer[index] = clamp_t(
                    255.0 as Float * gamma_correct(rgb[index]) + 0.5,
                    0.0 as Float,
                    255.0 as Float,
                ) as u8;
                // green
                let index: usize = (3 * (y * width + x) + 1) as usize;
                buffer[index] = clamp_t(
                    255.0 as Float * gamma_correct(rgb[index]) + 0.5,
                    0.0 as Float,
                    255.0 as Float,
                ) as u8;
                // blue
                let index: usize = (3 * (y * width + x) + 2) as usize;
                buffer[index] = clamp_t(
                    255.0 as Float * gamma_correct(rgb[index]) + 0.5,
                    0.0 as Float,
                    255.0 as Float,
                ) as u8;
            }
        }
        // write "pbrt.png" to disk
        image::save_buffer(
            &Path::new("pbrt.png"),
            &buffer,
            width,
            height,
            image::ColorType::Rgb8,
        )
        .unwrap();
    }
    // pub fn get_pixel<'a>(&self, p: &Point2i) -> &'a Pixel {
    //     assert!(pnt2_inside_exclusivei(p, &self.cropped_pixel_bounds));
    //     let width: i32 = self.cropped_pixel_bounds.p_max.x - self.cropped_pixel_bounds.p_min.x;
    //     let offset: i32 = (p.x - self.cropped_pixel_bounds.p_min.x)
    //         + (p.y - self.cropped_pixel_bounds.p_min.y) * width;
    //     &self.pixels.read().unwrap()[offset as usize]
    // }
}