bevy_pbr/fog.rs
1use bevy_camera::Camera;
2use bevy_color::{Color, ColorToComponents, LinearRgba};
3use bevy_ecs::prelude::*;
4use bevy_math::{ops, Vec3};
5use bevy_reflect::{std_traits::ReflectDefault, Reflect};
6use bevy_render::extract_component::ExtractComponent;
7
8/// Configures the “classic” computer graphics [distance fog](https://en.wikipedia.org/wiki/Distance_fog) effect,
9/// in which objects appear progressively more covered in atmospheric haze the further away they are from the camera.
10/// Affects meshes rendered via the PBR [`StandardMaterial`](crate::StandardMaterial).
11///
12/// ## Falloff
13///
14/// The rate at which fog intensity increases with distance is controlled by the falloff mode.
15/// Currently, the following fog falloff modes are supported:
16///
17/// - [`FogFalloff::Linear`]
18/// - [`FogFalloff::Exponential`]
19/// - [`FogFalloff::ExponentialSquared`]
20/// - [`FogFalloff::Atmospheric`]
21///
22/// ## Example
23///
24/// ```
25/// # use bevy_ecs::prelude::*;
26/// # use bevy_render::prelude::*;
27/// # use bevy_camera::prelude::*;
28/// # use bevy_pbr::prelude::*;
29/// # use bevy_color::Color;
30/// # fn system(mut commands: Commands) {
31/// commands.spawn((
32/// // Setup your camera as usual
33/// Camera3d::default(),
34/// // Add fog to the same entity
35/// DistanceFog {
36/// color: Color::WHITE,
37/// falloff: FogFalloff::Exponential { density: 1e-3 },
38/// ..Default::default()
39/// },
40/// ));
41/// # }
42/// # bevy_ecs::system::assert_is_system(system);
43/// ```
44///
45/// ## Material Override
46///
47/// Once enabled for a specific camera, the fog effect can also be disabled for individual
48/// [`StandardMaterial`](crate::StandardMaterial) instances via the `fog_enabled` flag.
49#[derive(Debug, Clone, Component, Reflect, ExtractComponent)]
50#[extract_component_filter(With<Camera>)]
51#[reflect(Component, Default, Debug, Clone)]
52pub struct DistanceFog {
53 /// The color of the fog effect.
54 ///
55 /// **Tip:** The alpha channel of the color can be used to “modulate” the fog effect without
56 /// changing the fog falloff mode or parameters.
57 pub color: Color,
58
59 /// Color used to modulate the influence of directional light colors on the
60 /// fog, where the view direction aligns with each directional light direction,
61 /// producing a “glow” or light dispersion effect. (e.g. around the sun)
62 ///
63 /// Use [`Color::NONE`] to disable the effect.
64 pub directional_light_color: Color,
65
66 /// The exponent applied to the directional light alignment calculation.
67 /// A higher value means a more concentrated “glow”.
68 pub directional_light_exponent: f32,
69
70 /// Determines which falloff mode to use, and its parameters.
71 pub falloff: FogFalloff,
72}
73
74/// Allows switching between different fog falloff modes, and configuring their parameters.
75///
76/// ## Convenience Methods
77///
78/// When using non-linear fog modes it can be hard to determine the right parameter values
79/// for a given scene.
80///
81/// For easier artistic control, instead of creating the enum variants directly, you can use the
82/// visibility-based convenience methods:
83///
84/// - For `FogFalloff::Exponential`:
85/// - [`FogFalloff::from_visibility()`]
86/// - [`FogFalloff::from_visibility_contrast()`]
87///
88/// - For `FogFalloff::ExponentialSquared`:
89/// - [`FogFalloff::from_visibility_squared()`]
90/// - [`FogFalloff::from_visibility_contrast_squared()`]
91///
92/// - For `FogFalloff::Atmospheric`:
93/// - [`FogFalloff::from_visibility_color()`]
94/// - [`FogFalloff::from_visibility_colors()`]
95/// - [`FogFalloff::from_visibility_contrast_color()`]
96/// - [`FogFalloff::from_visibility_contrast_colors()`]
97#[derive(Debug, Clone, Reflect)]
98#[reflect(Clone)]
99pub enum FogFalloff {
100 /// A linear fog falloff that grows in intensity between `start` and `end` distances.
101 ///
102 /// This falloff mode is simpler to control than other modes, however it can produce results that look “artificial”, depending on the scene.
103 ///
104 /// ## Formula
105 ///
106 /// The fog intensity for a given point in the scene is determined by the following formula:
107 ///
108 /// ```text
109 /// let fog_intensity = 1.0 - ((end - distance) / (end - start)).clamp(0.0, 1.0);
110 /// ```
111 ///
112 /// <svg width="370" height="212" viewBox="0 0 370 212" fill="none">
113 /// <title>Plot showing how linear fog falloff behaves for start and end values of 0.8 and 2.2, respectively.</title>
114 /// <path d="M331 151H42V49" stroke="currentColor" stroke-width="2"/>
115 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-family="Inter" font-size="12" letter-spacing="0em"><tspan x="136" y="173.864">1</tspan></text>
116 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-family="Inter" font-size="12" letter-spacing="0em"><tspan x="30" y="53.8636">1</tspan></text>
117 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-family="Inter" font-size="12" letter-spacing="0em"><tspan x="42" y="173.864">0</tspan></text>
118 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-family="Inter" font-size="12" letter-spacing="0em"><tspan x="232" y="173.864">2</tspan></text>
119 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-family="Inter" font-size="12" letter-spacing="0em"><tspan x="332" y="173.864">3</tspan></text>
120 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-family="Inter" font-size="12" letter-spacing="0em"><tspan x="161" y="190.864">distance</tspan></text>
121 /// <text font-family="sans-serif" transform="translate(10 132) rotate(-90)" fill="currentColor" style="white-space: pre" font-family="Inter" font-size="12" letter-spacing="0em"><tspan x="0" y="11.8636">fog intensity</tspan></text>
122 /// <path d="M43 150H117.227L263 48H331" stroke="#FF00E5"/>
123 /// <path d="M118 151V49" stroke="#FF00E5" stroke-dasharray="1 4"/>
124 /// <path d="M263 151V49" stroke="#FF00E5" stroke-dasharray="1 4"/>
125 /// <text font-family="sans-serif" fill="#FF00E5" style="white-space: pre" font-family="Inter" font-size="10" letter-spacing="0em"><tspan x="121" y="58.6364">start</tspan></text>
126 /// <text font-family="sans-serif" fill="#FF00E5" style="white-space: pre" font-family="Inter" font-size="10" letter-spacing="0em"><tspan x="267" y="58.6364">end</tspan></text>
127 /// </svg>
128 Linear {
129 /// Distance from the camera where fog is completely transparent, in world units.
130 start: f32,
131
132 /// Distance from the camera where fog is completely opaque, in world units.
133 end: f32,
134 },
135
136 /// An exponential fog falloff with a given `density`.
137 ///
138 /// Initially gains intensity quickly with distance, then more slowly. Typically produces more natural results than [`FogFalloff::Linear`],
139 /// but is a bit harder to control.
140 ///
141 /// To move the fog “further away”, use lower density values. To move it “closer” use higher density values.
142 ///
143 /// ## Tips
144 ///
145 /// - Use the [`FogFalloff::from_visibility()`] convenience method to create an exponential falloff with the proper
146 /// density for a desired visibility distance in world units;
147 /// - It's not _unusual_ to have very large or very small values for the density, depending on the scene
148 /// scale. Typically, for scenes with objects in the scale of thousands of units, you might want density values
149 /// in the ballpark of `0.001`. Conversely, for really small scale scenes you might want really high values of
150 /// density;
151 /// - Combine the `density` parameter with the [`DistanceFog`] `color`'s alpha channel for easier artistic control.
152 ///
153 /// ## Formula
154 ///
155 /// The fog intensity for a given point in the scene is determined by the following formula:
156 ///
157 /// ```text
158 /// let fog_intensity = 1.0 - 1.0 / (distance * density).exp();
159 /// ```
160 ///
161 /// <svg width="370" height="212" viewBox="0 0 370 212" fill="none">
162 /// <title>Plot showing how exponential fog falloff behaves for different density values</title>
163 /// <mask id="mask0_3_31" style="mask-type:alpha" maskUnits="userSpaceOnUse" x="42" y="42" width="286" height="108">
164 /// <rect x="42" y="42" width="286" height="108" fill="#D9D9D9"/>
165 /// </mask>
166 /// <g mask="url(#mask0_3_31)">
167 /// <path d="M42 150C42 150 98.3894 53 254.825 53L662 53" stroke="#FF003D" stroke-width="1"/>
168 /// <path d="M42 150C42 150 139.499 53 409.981 53L1114 53" stroke="#001AFF" stroke-width="1"/>
169 /// <path d="M42 150C42 150 206.348 53 662.281 53L1849 53" stroke="#14FF00" stroke-width="1"/>
170 /// </g>
171 /// <path d="M331 151H42V49" stroke="currentColor" stroke-width="2"/>
172 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-size="12" letter-spacing="0em"><tspan x="136" y="173.864">1</tspan></text>
173 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-size="12" letter-spacing="0em"><tspan x="30" y="53.8636">1</tspan></text>
174 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-size="12" letter-spacing="0em"><tspan x="42" y="173.864">0</tspan></text>
175 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-size="12" letter-spacing="0em"><tspan x="232" y="173.864">2</tspan></text>
176 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-size="12" letter-spacing="0em"><tspan x="332" y="173.864">3</tspan></text>
177 /// <text font-family="sans-serif" fill="#FF003D" style="white-space: pre" font-size="10" letter-spacing="0em"><tspan x="77" y="64.6364">density = 2</tspan></text>
178 /// <text font-family="sans-serif" fill="#001AFF" style="white-space: pre" font-size="10" letter-spacing="0em"><tspan x="236" y="76.6364">density = 1</tspan></text>
179 /// <text font-family="sans-serif" fill="#14FF00" style="white-space: pre" font-size="10" letter-spacing="0em"><tspan x="205" y="115.636">density = 0.5</tspan></text>
180 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-size="12" letter-spacing="0em"><tspan x="161" y="190.864">distance</tspan></text>
181 /// <text font-family="sans-serif" transform="translate(10 132) rotate(-90)" fill="currentColor" style="white-space: pre" font-size="12" letter-spacing="0em"><tspan x="0" y="11.8636">fog intensity</tspan></text>
182 /// </svg>
183 Exponential {
184 /// Multiplier applied to the world distance (within the exponential fog falloff calculation).
185 density: f32,
186 },
187
188 /// A squared exponential fog falloff with a given `density`.
189 ///
190 /// Similar to [`FogFalloff::Exponential`], but grows more slowly in intensity for closer distances
191 /// before “catching up”.
192 ///
193 /// To move the fog “further away”, use lower density values. To move it “closer” use higher density values.
194 ///
195 /// ## Tips
196 ///
197 /// - Use the [`FogFalloff::from_visibility_squared()`] convenience method to create an exponential squared falloff
198 /// with the proper density for a desired visibility distance in world units;
199 /// - Combine the `density` parameter with the [`DistanceFog`] `color`'s alpha channel for easier artistic control.
200 ///
201 /// ## Formula
202 ///
203 /// The fog intensity for a given point in the scene is determined by the following formula:
204 ///
205 /// ```text
206 /// let fog_intensity = 1.0 - 1.0 / (distance * density).squared().exp();
207 /// ```
208 ///
209 /// <svg width="370" height="212" viewBox="0 0 370 212" fill="none">
210 /// <title>Plot showing how exponential squared fog falloff behaves for different density values</title>
211 /// <mask id="mask0_1_3" style="mask-type:alpha" maskUnits="userSpaceOnUse" x="42" y="42" width="286" height="108">
212 /// <rect x="42" y="42" width="286" height="108" fill="#D9D9D9"/>
213 /// </mask>
214 /// <g mask="url(#mask0_1_3)">
215 /// <path d="M42 150C75.4552 150 74.9241 53.1724 166.262 53.1724L404 53.1724" stroke="#FF003D" stroke-width="1"/>
216 /// <path d="M42 150C107.986 150 106.939 53.1724 287.091 53.1724L756 53.1724" stroke="#001AFF" stroke-width="1"/>
217 /// <path d="M42 150C166.394 150 164.42 53.1724 504.035 53.1724L1388 53.1724" stroke="#14FF00" stroke-width="1"/>
218 /// </g>
219 /// <path d="M331 151H42V49" stroke="currentColor" stroke-width="2"/>
220 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-size="12" letter-spacing="0em"><tspan x="136" y="173.864">1</tspan></text>
221 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-size="12" letter-spacing="0em"><tspan x="30" y="53.8636">1</tspan></text>
222 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-size="12" letter-spacing="0em"><tspan x="42" y="173.864">0</tspan></text>
223 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-size="12" letter-spacing="0em"><tspan x="232" y="173.864">2</tspan></text>
224 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-size="12" letter-spacing="0em"><tspan x="332" y="173.864">3</tspan></text>
225 /// <text font-family="sans-serif" fill="#FF003D" style="white-space: pre" font-size="10" letter-spacing="0em"><tspan x="61" y="54.6364">density = 2</tspan></text>
226 /// <text font-family="sans-serif" fill="#001AFF" style="white-space: pre" font-size="10" letter-spacing="0em"><tspan x="168" y="84.6364">density = 1</tspan></text>
227 /// <text font-family="sans-serif" fill="#14FF00" style="white-space: pre" font-size="10" letter-spacing="0em"><tspan x="174" y="121.636">density = 0.5</tspan></text>
228 /// <text font-family="sans-serif" fill="currentColor" style="white-space: pre" font-size="12" letter-spacing="0em"><tspan x="161" y="190.864">distance</tspan></text>
229 /// <text font-family="sans-serif" transform="translate(10 132) rotate(-90)" fill="currentColor" style="white-space: pre" font-size="12" letter-spacing="0em"><tspan x="0" y="11.8636">fog intensity</tspan></text>
230 /// </svg>
231 ExponentialSquared {
232 /// Multiplier applied to the world distance (within the exponential squared fog falloff calculation).
233 density: f32,
234 },
235
236 /// A more general form of the [`FogFalloff::Exponential`] mode. The falloff formula is separated into
237 /// two terms, `extinction` and `inscattering`, for a somewhat simplified atmospheric scattering model.
238 /// Additionally, individual color channels can have their own density values, resulting in a total of
239 /// six different configuration parameters.
240 ///
241 /// ## Tips
242 ///
243 /// - Use the [`FogFalloff::from_visibility_colors()`] or [`FogFalloff::from_visibility_color()`] convenience methods
244 /// to create an atmospheric falloff with the proper densities for a desired visibility distance in world units and
245 /// extinction and inscattering colors;
246 /// - Combine the atmospheric fog parameters with the [`DistanceFog`] `color`'s alpha channel for easier artistic control.
247 ///
248 /// ## Formula
249 ///
250 /// Unlike other modes, atmospheric falloff doesn't use a simple intensity-based blend of fog color with
251 /// object color. Instead, it calculates per-channel extinction and inscattering factors, which are
252 /// then used to calculate the final color.
253 ///
254 /// ```text
255 /// let extinction_factor = 1.0 - 1.0 / (distance * extinction).exp();
256 /// let inscattering_factor = 1.0 - 1.0 / (distance * inscattering).exp();
257 /// let result = input_color * (1.0 - extinction_factor) + fog_color * inscattering_factor;
258 /// ```
259 ///
260 /// ## Equivalence to [`FogFalloff::Exponential`]
261 ///
262 /// For a density value of `D`, the following two falloff modes will produce identical visual results:
263 ///
264 /// ```
265 /// # use bevy_pbr::prelude::*;
266 /// # use bevy_math::prelude::*;
267 /// # const D: f32 = 0.5;
268 /// #
269 /// let exponential = FogFalloff::Exponential {
270 /// density: D,
271 /// };
272 ///
273 /// let atmospheric = FogFalloff::Atmospheric {
274 /// extinction: Vec3::new(D, D, D),
275 /// inscattering: Vec3::new(D, D, D),
276 /// };
277 /// ```
278 ///
279 /// **Note:** While the results are identical, [`FogFalloff::Atmospheric`] is computationally more expensive.
280 Atmospheric {
281 /// Controls how much light is removed due to atmospheric “extinction”, i.e. loss of light due to
282 /// photons being absorbed by atmospheric particles.
283 ///
284 /// Each component can be thought of as an independent per `R`/`G`/`B` channel `density` factor from
285 /// [`FogFalloff::Exponential`]: Multiplier applied to the world distance (within the fog
286 /// falloff calculation) for that specific channel.
287 ///
288 /// **Note:**
289 /// This value is not a `Color`, since it affects the channels exponentially in a non-intuitive way.
290 /// For artistic control, use the [`FogFalloff::from_visibility_colors()`] convenience method.
291 extinction: Vec3,
292
293 /// Controls how much light is added due to light scattering from the sun through the atmosphere.
294 ///
295 /// Each component can be thought of as an independent per `R`/`G`/`B` channel `density` factor from
296 /// [`FogFalloff::Exponential`]: A multiplier applied to the world distance (within the fog
297 /// falloff calculation) for that specific channel.
298 ///
299 /// **Note:**
300 /// This value is not a `Color`, since it affects the channels exponentially in a non-intuitive way.
301 /// For artistic control, use the [`FogFalloff::from_visibility_colors()`] convenience method.
302 inscattering: Vec3,
303 },
304}
305
306impl FogFalloff {
307 /// Creates a [`FogFalloff::Exponential`] value from the given visibility distance in world units,
308 /// using the revised Koschmieder contrast threshold, [`FogFalloff::REVISED_KOSCHMIEDER_CONTRAST_THRESHOLD`].
309 pub fn from_visibility(visibility: f32) -> FogFalloff {
310 FogFalloff::from_visibility_contrast(
311 visibility,
312 FogFalloff::REVISED_KOSCHMIEDER_CONTRAST_THRESHOLD,
313 )
314 }
315
316 /// Creates a [`FogFalloff::Exponential`] value from the given visibility distance in world units,
317 /// and a given contrast threshold in the range of `0.0` to `1.0`.
318 pub fn from_visibility_contrast(visibility: f32, contrast_threshold: f32) -> FogFalloff {
319 FogFalloff::Exponential {
320 density: FogFalloff::koschmieder(visibility, contrast_threshold),
321 }
322 }
323
324 /// Creates a [`FogFalloff::ExponentialSquared`] value from the given visibility distance in world units,
325 /// using the revised Koschmieder contrast threshold, [`FogFalloff::REVISED_KOSCHMIEDER_CONTRAST_THRESHOLD`].
326 pub fn from_visibility_squared(visibility: f32) -> FogFalloff {
327 FogFalloff::from_visibility_contrast_squared(
328 visibility,
329 FogFalloff::REVISED_KOSCHMIEDER_CONTRAST_THRESHOLD,
330 )
331 }
332
333 /// Creates a [`FogFalloff::ExponentialSquared`] value from the given visibility distance in world units,
334 /// and a given contrast threshold in the range of `0.0` to `1.0`.
335 pub fn from_visibility_contrast_squared(
336 visibility: f32,
337 contrast_threshold: f32,
338 ) -> FogFalloff {
339 FogFalloff::ExponentialSquared {
340 density: (FogFalloff::koschmieder(visibility, contrast_threshold) / visibility).sqrt(),
341 }
342 }
343
344 /// Creates a [`FogFalloff::Atmospheric`] value from the given visibility distance in world units,
345 /// and a shared color for both extinction and inscattering, using the revised Koschmieder contrast threshold,
346 /// [`FogFalloff::REVISED_KOSCHMIEDER_CONTRAST_THRESHOLD`].
347 pub fn from_visibility_color(
348 visibility: f32,
349 extinction_inscattering_color: Color,
350 ) -> FogFalloff {
351 FogFalloff::from_visibility_contrast_colors(
352 visibility,
353 FogFalloff::REVISED_KOSCHMIEDER_CONTRAST_THRESHOLD,
354 extinction_inscattering_color,
355 extinction_inscattering_color,
356 )
357 }
358
359 /// Creates a [`FogFalloff::Atmospheric`] value from the given visibility distance in world units,
360 /// extinction and inscattering colors, using the revised Koschmieder contrast threshold,
361 /// [`FogFalloff::REVISED_KOSCHMIEDER_CONTRAST_THRESHOLD`].
362 ///
363 /// ## Tips
364 /// - Alpha values of the provided colors can modulate the `extinction` and `inscattering` effects;
365 /// - Using an `extinction_color` of [`Color::WHITE`] or [`Color::NONE`] disables the extinction effect;
366 /// - Using an `inscattering_color` of [`Color::BLACK`] or [`Color::NONE`] disables the inscattering effect.
367 pub fn from_visibility_colors(
368 visibility: f32,
369 extinction_color: Color,
370 inscattering_color: Color,
371 ) -> FogFalloff {
372 FogFalloff::from_visibility_contrast_colors(
373 visibility,
374 FogFalloff::REVISED_KOSCHMIEDER_CONTRAST_THRESHOLD,
375 extinction_color,
376 inscattering_color,
377 )
378 }
379
380 /// Creates a [`FogFalloff::Atmospheric`] value from the given visibility distance in world units,
381 /// a contrast threshold in the range of `0.0` to `1.0`, and a shared color for both extinction and inscattering.
382 pub fn from_visibility_contrast_color(
383 visibility: f32,
384 contrast_threshold: f32,
385 extinction_inscattering_color: Color,
386 ) -> FogFalloff {
387 FogFalloff::from_visibility_contrast_colors(
388 visibility,
389 contrast_threshold,
390 extinction_inscattering_color,
391 extinction_inscattering_color,
392 )
393 }
394
395 /// Creates a [`FogFalloff::Atmospheric`] value from the given visibility distance in world units,
396 /// a contrast threshold in the range of `0.0` to `1.0`, extinction and inscattering colors.
397 ///
398 /// ## Tips
399 /// - Alpha values of the provided colors can modulate the `extinction` and `inscattering` effects;
400 /// - Using an `extinction_color` of [`Color::WHITE`] or [`Color::NONE`] disables the extinction effect;
401 /// - Using an `inscattering_color` of [`Color::BLACK`] or [`Color::NONE`] disables the inscattering effect.
402 pub fn from_visibility_contrast_colors(
403 visibility: f32,
404 contrast_threshold: f32,
405 extinction_color: Color,
406 inscattering_color: Color,
407 ) -> FogFalloff {
408 use core::f32::consts::E;
409
410 let [r_e, g_e, b_e, a_e] = LinearRgba::from(extinction_color).to_f32_array();
411 let [r_i, g_i, b_i, a_i] = LinearRgba::from(inscattering_color).to_f32_array();
412
413 FogFalloff::Atmospheric {
414 extinction: Vec3::new(
415 // Values are subtracted from 1.0 here to preserve the intuitive/artistic meaning of
416 // colors, since they're later subtracted. (e.g. by giving a blue extinction color, you
417 // get blue and _not_ yellow results)
418 ops::powf(1.0 - r_e, E),
419 ops::powf(1.0 - g_e, E),
420 ops::powf(1.0 - b_e, E),
421 ) * FogFalloff::koschmieder(visibility, contrast_threshold)
422 * ops::powf(a_e, E),
423
424 inscattering: Vec3::new(ops::powf(r_i, E), ops::powf(g_i, E), ops::powf(b_i, E))
425 * FogFalloff::koschmieder(visibility, contrast_threshold)
426 * ops::powf(a_i, E),
427 }
428 }
429
430 /// A 2% contrast threshold was originally proposed by Koschmieder, being the
431 /// minimum visual contrast at which a human observer could detect an object.
432 /// We use a revised 5% contrast threshold, deemed more realistic for typical human observers.
433 pub const REVISED_KOSCHMIEDER_CONTRAST_THRESHOLD: f32 = 0.05;
434
435 /// Calculates the extinction coefficient β, from V and Cₜ, where:
436 ///
437 /// - Cₜ is the contrast threshold, in the range of `0.0` to `1.0`
438 /// - V is the visibility distance in which a perfectly black object is still identifiable
439 /// against the horizon sky within the contrast threshold
440 ///
441 /// We start with Koschmieder's equation:
442 ///
443 /// ```text
444 /// -ln(Cₜ)
445 /// V = ─────────
446 /// β
447 /// ```
448 ///
449 /// Multiplying both sides by β/V, that gives us:
450 ///
451 /// ```text
452 /// -ln(Cₜ)
453 /// β = ─────────
454 /// V
455 /// ```
456 ///
457 /// See:
458 /// - <https://en.wikipedia.org/wiki/Visibility>
459 /// - <https://www.biral.com/wp-content/uploads/2015/02/Introduction_to_visibility-v2-2.pdf>
460 pub fn koschmieder(v: f32, c_t: f32) -> f32 {
461 -ops::ln(c_t) / v
462 }
463}
464
465impl Default for DistanceFog {
466 fn default() -> Self {
467 DistanceFog {
468 color: Color::WHITE,
469 falloff: FogFalloff::Linear {
470 start: 0.0,
471 end: 100.0,
472 },
473 directional_light_color: Color::NONE,
474 directional_light_exponent: 8.0,
475 }
476 }
477}