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
//! Metal texture generator — brushed finish or standing-seam roof panels,
//! with optional rust weathering.
//!
//! The algorithm:
//! 1. **Brushed**: anisotropic FBM — high frequency in U (many scratches),
//! very low frequency in V (scratches run nearly horizontally).
//! 2. **StandingSeam**: sinusoidal ridge profile across V, with micro-detail
//! FBM overlay.
//! 3. A separate low-frequency FBM drives rust-patch blending: rust areas
//! receive a warm colour, raised roughness, and reduced metallic value.
use std::f64::consts::TAU;
use noise::{Fbm, MultiFractal, NoiseFn, Perlin};
use crate::{
generator::{TextureError, TextureGenerator, TextureMap, linear_to_srgb, validate_dimensions},
noise::{ToroidalNoise, normalize, sample_grid},
normal::{BoundaryMode, height_to_normal},
};
/// Visual style of the metal surface.
#[derive(Clone, Debug, PartialEq, serde::Serialize, serde::Deserialize)]
pub enum MetalStyle {
/// Fine horizontal scratches (brushed / satin finish).
Brushed,
/// Parallel raised ridges running across the tile (standing-seam roof).
StandingSeam,
}
/// Configures the appearance of a [`MetalGenerator`].
#[derive(Clone, Debug, serde::Serialize, serde::Deserialize)]
pub struct MetalConfig {
/// PRNG seed for the deterministic noise pattern; different seeds give
/// statistically-different textures from otherwise-identical configs.
pub seed: u32,
/// Surface finish style.
pub style: MetalStyle,
/// Base noise scale.
pub scale: f64,
/// For `StandingSeam`: number of ridges across the tile.
pub seam_count: f64,
/// Ridge sharpness for `StandingSeam` \[0.5 = sinusoidal, 4.0 = sharp\].
pub seam_sharpness: f64,
/// Anisotropy factor for `Brushed` — higher = longer horizontal scratches.
pub brush_stretch: f64,
/// Micro-roughness amplitude \[0, 1\].
pub roughness: f64,
/// Metallic value for clean (rust-free) areas \[0, 1\].
pub metallic: f32,
/// Rust-patch coverage \[0 = none, 1 = heavy\].
pub rust_level: f64,
/// Base metal colour in linear RGB \[0, 1\].
pub color_metal: [f32; 3],
/// Rust colour in linear RGB \[0, 1\].
pub color_rust: [f32; 3],
/// Normal-map strength.
pub normal_strength: f32,
}
impl Default for MetalConfig {
fn default() -> Self {
Self {
seed: 31,
style: MetalStyle::Brushed,
scale: 6.0,
seam_count: 6.0,
seam_sharpness: 2.5,
brush_stretch: 8.0,
roughness: 0.25,
metallic: 0.85,
rust_level: 0.15,
color_metal: [0.42, 0.44, 0.47],
color_rust: [0.42, 0.24, 0.12],
normal_strength: 3.0,
}
}
}
/// Procedural metal texture generator.
///
/// Drives [`TextureGenerator::generate`] using a [`MetalConfig`]. Construct
/// via [`MetalGenerator::new`] and call `generate` directly, or spawn a
/// [`crate::async_gen::PendingTexture::metal`] task for non-blocking generation.
///
/// Noise objects are built in the constructor so that calling `generate`
/// multiple times (e.g. producing size variants of the same material)
/// does not repeat the initialisation cost.
pub struct MetalGenerator {
config: MetalConfig,
fbm_scratch: Fbm<Perlin>,
rust_noise: ToroidalNoise<Fbm<Perlin>>,
}
impl MetalGenerator {
/// Create a new generator with the given configuration.
///
/// Builds the noise objects up front so that repeated
/// calls to [`generate`](TextureGenerator::generate) skip initialisation.
pub fn new(config: MetalConfig) -> Self {
let fbm_scratch: Fbm<Perlin> = Fbm::new(config.seed).set_octaves(5);
let fbm_rust: Fbm<Perlin> = Fbm::new(config.seed.wrapping_add(41)).set_octaves(4);
let rust_noise = ToroidalNoise::new(fbm_rust, config.scale * 0.4);
Self {
config,
fbm_scratch,
rust_noise,
}
}
}
impl TextureGenerator for MetalGenerator {
fn generate(&self, width: u32, height: u32) -> Result<TextureMap, TextureError> {
validate_dimensions(width, height)?;
let c = &self.config;
// Rust patches — separate seed, low frequency for large blotches.
let rust_grid = sample_grid(&self.rust_noise, width, height);
let w = width as usize;
let h = height as usize;
let n = w * h;
let mut heights = vec![0.0f64; n];
let mut albedo = vec![0u8; n * 4];
let mut roughness_buf = vec![0u8; n * 4];
for y in 0..h {
let v = y as f64 / h as f64;
// Standing-seam ridge profile (sinusoidal bumps in V).
// seam_count must be an integer for the pattern to tile; round to nearest.
let seam_count = c.seam_count.round();
let seam_h = if c.style == MetalStyle::StandingSeam {
let phase = (v * seam_count * TAU).sin();
// Raise to power to sharpen; clamp to [0,1].
phase.abs().powf(c.seam_sharpness.max(0.1)) * phase.signum() * 0.5 + 0.5
} else {
0.0
};
for x in 0..w {
let u = x as f64 / w as f64;
// Sample scratch noise.
// Brushed: large radius in U (fast oscillations → many horizontal
// scratches), small radius in V (slow → scratches run lengthwise).
// StandingSeam: uniform toroidal sampling for micro-detail.
let scratch = match c.style {
MetalStyle::Brushed => {
let nx = (TAU * u).cos() * c.scale * c.brush_stretch;
let ny = (TAU * u).sin() * c.scale * c.brush_stretch;
let nz = (TAU * v).cos() * c.scale * 0.12;
let nw = (TAU * v).sin() * c.scale * 0.12;
self.fbm_scratch.get([nx, ny, nz, nw]) * 0.5 + 0.5
}
MetalStyle::StandingSeam => {
let nx = (TAU * u).cos() * c.scale;
let ny = (TAU * u).sin() * c.scale;
let nz = (TAU * v).cos() * c.scale;
let nw = (TAU * v).sin() * c.scale;
self.fbm_scratch.get([nx, ny, nz, nw]) * 0.5 + 0.5
}
};
let idx = y * w + x;
let rust_t = normalize(rust_grid[idx]);
// Soft threshold → rust coverage.
let rust_blend = ((rust_t - (1.0 - c.rust_level)).clamp(0.0, c.rust_level)
/ c.rust_level.max(1e-9))
.clamp(0.0, 1.0);
let h_scratch = scratch * c.roughness * 0.3;
let h_val = match c.style {
MetalStyle::Brushed => h_scratch,
MetalStyle::StandingSeam => seam_h * 0.7 + h_scratch * 0.3,
};
heights[idx] = h_val;
// Colour: lerp metal → rust.
let r = lerp(c.color_metal[0], c.color_rust[0], rust_blend as f32);
let g = lerp(c.color_metal[1], c.color_rust[1], rust_blend as f32);
let b = lerp(c.color_metal[2], c.color_rust[2], rust_blend as f32);
let ai = idx * 4;
albedo[ai] = linear_to_srgb(r);
albedo[ai + 1] = linear_to_srgb(g);
albedo[ai + 2] = linear_to_srgb(b);
albedo[ai + 3] = 255;
// ORM: rust raises roughness and kills metallic.
let rough = (c.roughness as f32 + rust_blend as f32 * 0.65).clamp(0.0, 1.0);
let met = (c.metallic - rust_blend as f32 * 0.80).clamp(0.0, 1.0);
roughness_buf[ai] = 255;
roughness_buf[ai + 1] = (rough * 255.0).round() as u8;
roughness_buf[ai + 2] = (met * 255.0).round() as u8;
roughness_buf[ai + 3] = 255;
}
}
let normal = height_to_normal(
&heights,
width,
height,
c.normal_strength,
BoundaryMode::Wrap,
);
Ok(TextureMap {
albedo,
normal,
roughness: roughness_buf,
width,
height,
})
}
}
#[inline]
fn lerp(a: f32, b: f32, t: f32) -> f32 {
a + (b - a) * t.clamp(0.0, 1.0)
}