alice-sdf 6.0.0

//! Shader-language helper strings for the NPR primitives
//!
//! Static source snippets for GLSL, WGSL, and HLSL that reproduce the
//! Rust NPR primitives on the GPU. Callers concatenate the appropriate
//! constant with their own shader source to make the helpers available.
//!
//! Two sets of helpers are provided:
//! - **Core** (`NPR_*_HELPERS`): 15 fixed-arity scalar / vector primitives
//!   (`toon_ramp`, `distance_field_outline_soft`, `fresnel_rim`,
//!   `vignette`, `sun_disc`, etc.)
//! - **Palette** (`NPR_*_PALETTE_HELPERS`): fixed-anchor palette variants
//!   that replace the Rust `&[Vec3]` slice API with explicit `N` color
//!   arguments: `sky_gradient_bands_3`, `palette_gradient_5`,
//!   `time_of_day`, `season_palette`
//!
//! Callers may `format!("{}{}", NPR_GLSL_HELPERS, NPR_GLSL_PALETTE_HELPERS)`
//! to inject the full set at once.
//!
//! Author: Moroya Sakamoto

// ============================================================================
// GLSL (OpenGL / Vulkan)
// ============================================================================

/// GLSL 330+ helpers for the NPR primitives with fixed-arity signatures
pub const NPR_GLSL_HELPERS: &str = r"
// ALICE-SDF NPR helpers (GLSL 330+)

float alice_toon_ramp(float n_dot_l, float bands) {
    float c = clamp(n_dot_l, 0.0, 1.0);
    float idx = min(floor(c * bands), bands - 1.0);
    return idx / max(bands - 1.0, 1.0);
}

float alice_soft_toon_ramp(float n_dot_l, float bands, float smoothness) {
    float c = clamp(n_dot_l, 0.0, 1.0);
    float scaled = c * bands;
    float idx = min(floor(scaled), bands - 1.0);
    float frac_ = clamp(scaled - idx, 0.0, 1.0);
    float s = clamp(smoothness, 0.001, 0.5);
    float t = smoothstep(0.5 - s, 0.5 + s, frac_);
    return clamp((idx + t) / bands, 0.0, 1.0);
}

vec3 alice_two_tone(float n_dot_l, vec3 shadow, vec3 light, float threshold) {
    return mix(shadow, light, step(threshold, clamp(n_dot_l, 0.0, 1.0)));
}

vec3 alice_posterize_color(vec3 color, float levels) {
    vec3 c = clamp(color, vec3(0.0), vec3(1.0));
    float denom = max(levels - 1.0, 1.0);
    return clamp(floor(c * levels) / denom, vec3(0.0), vec3(1.0));
}

float alice_distance_field_outline(float sdf_v, float width) {
    return step(abs(sdf_v), max(width, 0.0));
}

float alice_distance_field_outline_soft(float sdf_v, float width_inner, float width_outer) {
    float d = abs(sdf_v);
    float inner = max(width_inner, 0.0);
    float outer = max(width_outer, inner + 1e-6);
    if (d <= inner) return 1.0;
    if (d >= outer) return 0.0;
    float t = clamp((d - inner) / (outer - inner), 0.0, 1.0);
    return 1.0 - (t * t * (3.0 - 2.0 * t));
}

vec3 alice_composite_outline(vec3 base, vec3 outline_col, float alpha) {
    return mix(base, outline_col, clamp(alpha, 0.0, 1.0));
}

float alice_fresnel_rim(float n_dot_v, float power, float intensity) {
    float base = max(1.0 - clamp(n_dot_v, 0.0, 1.0), 0.0);
    return pow(base, max(power, 0.0)) * intensity;
}

vec3 alice_procedural_matcap(vec3 normal_view, vec3 bl, vec3 br, vec3 tl, vec3 tr) {
    float u = clamp(normal_view.x * 0.5 + 0.5, 0.0, 1.0);
    float v = clamp(normal_view.y * 0.5 + 0.5, 0.0, 1.0);
    vec3 bottom = mix(bl, br, u);
    vec3 top = mix(tl, tr, u);
    return mix(bottom, top, v);
}

float alice_stylized_specular(float n_dot_h, float sharpness, float soft_edge) {
    float ndh = clamp(n_dot_h, 0.0, 1.0);
    float raw = pow(ndh, max(sharpness, 1.0));
    float s = clamp(soft_edge, 0.0, 0.5);
    if (s < 1e-6) return step(0.5, raw);
    return smoothstep(0.5 - s, 0.5 + s, raw);
}

float alice_vignette(vec2 uv, float radius, float softness) {
    vec2 d = uv - vec2(0.5);
    float len = length(d);
    float inner = max(radius, 0.0);
    float outer = max(inner + max(softness, 0.0), inner + 1e-6);
    if (len <= inner) return 1.0;
    if (len >= outer) return 0.0;
    float t = clamp((len - inner) / (outer - inner), 0.0, 1.0);
    return 1.0 - (t * t * (3.0 - 2.0 * t));
}

vec3 alice_bloom_toon(vec3 color, float threshold, float intensity) {
    float m = max(max(color.r, color.g), color.b);
    return (m > threshold) ? color * intensity : vec3(0.0);
}

float alice_puffy_cloud_layer(float noise_sample, float coverage, float softness) {
    float n = clamp(noise_sample, 0.0, 1.0);
    float c = clamp(coverage, 0.0, 1.0);
    float s = max(softness, 1e-4);
    return clamp((n - (1.0 - c)) / s, 0.0, 1.0);
}

float alice_light_shaft_beam(vec3 view_dir, vec3 to_sun, float density) {
    vec3 v = normalize(view_dir + vec3(1e-8));
    vec3 s = normalize(to_sun + vec3(1e-8));
    float cos_theta = max(dot(v, s), 0.0);
    return pow(cos_theta, max(density, 1.0));
}

float alice_impact_flash(float t, float decay, float intensity) {
    if (t < 0.0) return 0.0;
    return intensity * exp(-t / max(decay, 1e-4));
}

float alice_sun_disc(vec3 view, vec3 to_sun, float radius, float softness) {
    vec3 v = normalize(view + vec3(1e-8));
    vec3 s = normalize(to_sun + vec3(1e-8));
    float cos_theta = dot(v, s);
    float r = max(radius, 0.0);
    float soft = max(softness, 0.0);
    float cos_inner = cos(r);
    float cos_outer = cos(r + soft);
    if (cos_theta >= cos_inner) return 1.0;
    if (cos_theta <= cos_outer) return 0.0;
    float denom = max(cos_inner - cos_outer, 1e-6);
    return clamp((cos_theta - cos_outer) / denom, 0.0, 1.0);
}

vec3 alice_saturate(vec3 color, float factor) {
    float lum = dot(color, vec3(0.2126, 0.7152, 0.0722));
    vec3 grey = vec3(lum);
    return mix(grey, color, factor);
}

float alice_hatch_lines(vec2 uv, float angle_rad, float density, float thickness) {
    float s = sin(angle_rad);
    float c = cos(angle_rad);
    float projected = uv.x * (-s) + uv.y * c;
    float d = max(density, 1e-6);
    float raw = projected * d;
    float phase = raw - floor(raw);
    float dist = abs(phase - 0.5);
    float t = clamp(thickness, 0.0, 0.5);
    return (dist > 0.5 - t) ? 1.0 : 0.0;
}

vec3 alice_tonemap_reinhard(vec3 color, float exposure) {
    vec3 c = color * max(exposure, 0.0);
    return c / (vec3(1.0) + c);
}

float alice_speed_line(vec2 uv, vec2 focus, float count, float thickness) {
    vec2 d = uv - focus;
    if (abs(d.x) < 1e-6 && abs(d.y) < 1e-6) return 0.0;
    if (count <= 0.0) return 0.0;
    float angle = atan(d.y, d.x);
    float TAU = 6.28318530718;
    float phase_raw = (angle + 3.14159265359) * count / TAU;
    float phase = phase_raw - floor(phase_raw);
    float dist = abs(phase - 0.5);
    float t = clamp(thickness, 0.0, 0.5);
    return (dist > 0.5 - t) ? 1.0 : 0.0;
}
";

// ============================================================================
// WGSL (WebGPU)
// ============================================================================

/// WGSL helpers matching the GLSL set above
pub const NPR_WGSL_HELPERS: &str = r"
// ALICE-SDF NPR helpers (WGSL)

fn alice_toon_ramp(n_dot_l: f32, bands: f32) -> f32 {
    let c = clamp(n_dot_l, 0.0, 1.0);
    let idx = min(floor(c * bands), bands - 1.0);
    return idx / max(bands - 1.0, 1.0);
}

fn alice_soft_toon_ramp(n_dot_l: f32, bands: f32, smoothness: f32) -> f32 {
    let c = clamp(n_dot_l, 0.0, 1.0);
    let scaled = c * bands;
    let idx = min(floor(scaled), bands - 1.0);
    let frac_val = clamp(scaled - idx, 0.0, 1.0);
    let s = clamp(smoothness, 0.001, 0.5);
    let t = smoothstep(0.5 - s, 0.5 + s, frac_val);
    return clamp((idx + t) / bands, 0.0, 1.0);
}

fn alice_two_tone(n_dot_l: f32, shadow: vec3<f32>, light: vec3<f32>, threshold: f32) -> vec3<f32> {
    return mix(shadow, light, vec3<f32>(step(threshold, clamp(n_dot_l, 0.0, 1.0))));
}

fn alice_posterize_color(color: vec3<f32>, levels: f32) -> vec3<f32> {
    let c = clamp(color, vec3<f32>(0.0), vec3<f32>(1.0));
    let denom = max(levels - 1.0, 1.0);
    return clamp(floor(c * levels) / denom, vec3<f32>(0.0), vec3<f32>(1.0));
}

fn alice_distance_field_outline(sdf_v: f32, width: f32) -> f32 {
    return step(abs(sdf_v), max(width, 0.0));
}

fn alice_distance_field_outline_soft(sdf_v: f32, width_inner: f32, width_outer: f32) -> f32 {
    let d = abs(sdf_v);
    let inner = max(width_inner, 0.0);
    let outer = max(width_outer, inner + 1e-6);
    if (d <= inner) { return 1.0; }
    if (d >= outer) { return 0.0; }
    let t = clamp((d - inner) / (outer - inner), 0.0, 1.0);
    return 1.0 - (t * t * (3.0 - 2.0 * t));
}

fn alice_composite_outline(base: vec3<f32>, outline_col: vec3<f32>, alpha: f32) -> vec3<f32> {
    return mix(base, outline_col, vec3<f32>(clamp(alpha, 0.0, 1.0)));
}

fn alice_fresnel_rim(n_dot_v: f32, power: f32, intensity: f32) -> f32 {
    let base = max(1.0 - clamp(n_dot_v, 0.0, 1.0), 0.0);
    return pow(base, max(power, 0.0)) * intensity;
}

fn alice_procedural_matcap(
    normal_view: vec3<f32>,
    bl: vec3<f32>, br: vec3<f32>,
    tl: vec3<f32>, tr: vec3<f32>,
) -> vec3<f32> {
    let u = clamp(normal_view.x * 0.5 + 0.5, 0.0, 1.0);
    let v = clamp(normal_view.y * 0.5 + 0.5, 0.0, 1.0);
    let bottom = mix(bl, br, vec3<f32>(u));
    let top = mix(tl, tr, vec3<f32>(u));
    return mix(bottom, top, vec3<f32>(v));
}

fn alice_stylized_specular(n_dot_h: f32, sharpness: f32, soft_edge: f32) -> f32 {
    let ndh = clamp(n_dot_h, 0.0, 1.0);
    let raw = pow(ndh, max(sharpness, 1.0));
    let s = clamp(soft_edge, 0.0, 0.5);
    if (s < 1e-6) { return step(0.5, raw); }
    return smoothstep(0.5 - s, 0.5 + s, raw);
}

fn alice_vignette(uv: vec2<f32>, radius: f32, softness: f32) -> f32 {
    let d = uv - vec2<f32>(0.5, 0.5);
    let len = length(d);
    let inner = max(radius, 0.0);
    let outer = max(inner + max(softness, 0.0), inner + 1e-6);
    if (len <= inner) { return 1.0; }
    if (len >= outer) { return 0.0; }
    let t = clamp((len - inner) / (outer - inner), 0.0, 1.0);
    return 1.0 - (t * t * (3.0 - 2.0 * t));
}

fn alice_bloom_toon(color: vec3<f32>, threshold: f32, intensity: f32) -> vec3<f32> {
    let m = max(max(color.r, color.g), color.b);
    if (m > threshold) { return color * intensity; }
    return vec3<f32>(0.0, 0.0, 0.0);
}

fn alice_puffy_cloud_layer(noise_sample: f32, coverage: f32, softness: f32) -> f32 {
    let n = clamp(noise_sample, 0.0, 1.0);
    let c = clamp(coverage, 0.0, 1.0);
    let s = max(softness, 1e-4);
    return clamp((n - (1.0 - c)) / s, 0.0, 1.0);
}

fn alice_light_shaft_beam(view_dir: vec3<f32>, to_sun: vec3<f32>, density: f32) -> f32 {
    let v = normalize(view_dir + vec3<f32>(1e-8));
    let s = normalize(to_sun + vec3<f32>(1e-8));
    let cos_theta = max(dot(v, s), 0.0);
    return pow(cos_theta, max(density, 1.0));
}

fn alice_impact_flash(t: f32, decay: f32, intensity: f32) -> f32 {
    if (t < 0.0) { return 0.0; }
    return intensity * exp(-t / max(decay, 1e-4));
}

fn alice_sun_disc(view: vec3<f32>, to_sun: vec3<f32>, radius: f32, softness: f32) -> f32 {
    let v = normalize(view + vec3<f32>(1e-8));
    let s = normalize(to_sun + vec3<f32>(1e-8));
    let cos_theta = dot(v, s);
    let r = max(radius, 0.0);
    let soft = max(softness, 0.0);
    let cos_inner = cos(r);
    let cos_outer = cos(r + soft);
    if (cos_theta >= cos_inner) { return 1.0; }
    if (cos_theta <= cos_outer) { return 0.0; }
    let denom = max(cos_inner - cos_outer, 1e-6);
    return clamp((cos_theta - cos_outer) / denom, 0.0, 1.0);
}

fn alice_saturate(color: vec3<f32>, factor: f32) -> vec3<f32> {
    let lum = dot(color, vec3<f32>(0.2126, 0.7152, 0.0722));
    let grey = vec3<f32>(lum, lum, lum);
    return mix(grey, color, vec3<f32>(factor));
}

fn alice_hatch_lines(uv: vec2<f32>, angle_rad: f32, density: f32, thickness: f32) -> f32 {
    let s = sin(angle_rad);
    let c = cos(angle_rad);
    let projected = uv.x * (-s) + uv.y * c;
    let d = max(density, 1e-6);
    let raw = projected * d;
    let phase = raw - floor(raw);
    let dist = abs(phase - 0.5);
    let t = clamp(thickness, 0.0, 0.5);
    if (dist > 0.5 - t) { return 1.0; }
    return 0.0;
}

fn alice_tonemap_reinhard(color: vec3<f32>, exposure: f32) -> vec3<f32> {
    let c = color * max(exposure, 0.0);
    return c / (vec3<f32>(1.0, 1.0, 1.0) + c);
}

fn alice_speed_line(uv: vec2<f32>, focus: vec2<f32>, count: f32, thickness: f32) -> f32 {
    let d = uv - focus;
    if (abs(d.x) < 1e-6 && abs(d.y) < 1e-6) { return 0.0; }
    if (count <= 0.0) { return 0.0; }
    let angle = atan2(d.y, d.x);
    let TAU = 6.28318530718;
    let phase_raw = (angle + 3.14159265359) * count / TAU;
    let phase = phase_raw - floor(phase_raw);
    let dist = abs(phase - 0.5);
    let t = clamp(thickness, 0.0, 0.5);
    if (dist > 0.5 - t) { return 1.0; }
    return 0.0;
}
";

// ============================================================================
// HLSL (Direct3D)
// ============================================================================

/// HLSL Shader Model 5.0+ helpers matching the GLSL set
pub const NPR_HLSL_HELPERS: &str = r"
// ALICE-SDF NPR helpers (HLSL SM 5.0+)

float alice_toon_ramp(float n_dot_l, float bands) {
    float c = saturate(n_dot_l);
    float idx = min(floor(c * bands), bands - 1.0);
    return idx / max(bands - 1.0, 1.0);
}

float alice_soft_toon_ramp(float n_dot_l, float bands, float smoothness) {
    float c = saturate(n_dot_l);
    float scaled = c * bands;
    float idx = min(floor(scaled), bands - 1.0);
    float frac_val = saturate(scaled - idx);
    float s = clamp(smoothness, 0.001, 0.5);
    float t = smoothstep(0.5 - s, 0.5 + s, frac_val);
    return saturate((idx + t) / bands);
}

float3 alice_two_tone(float n_dot_l, float3 shadow, float3 light, float threshold) {
    return lerp(shadow, light, step(threshold, saturate(n_dot_l)));
}

float3 alice_posterize_color(float3 color, float levels) {
    float3 c = saturate(color);
    float denom = max(levels - 1.0, 1.0);
    return saturate(floor(c * levels) / denom);
}

float alice_distance_field_outline(float sdf_v, float width) {
    return step(abs(sdf_v), max(width, 0.0));
}

float alice_distance_field_outline_soft(float sdf_v, float width_inner, float width_outer) {
    float d = abs(sdf_v);
    float inner = max(width_inner, 0.0);
    float outer = max(width_outer, inner + 1e-6);
    if (d <= inner) return 1.0;
    if (d >= outer) return 0.0;
    float t = saturate((d - inner) / (outer - inner));
    return 1.0 - (t * t * (3.0 - 2.0 * t));
}

float3 alice_composite_outline(float3 base, float3 outline_col, float alpha) {
    return lerp(base, outline_col, saturate(alpha));
}

float alice_fresnel_rim(float n_dot_v, float power, float intensity) {
    float base = max(1.0 - saturate(n_dot_v), 0.0);
    return pow(base, max(power, 0.0)) * intensity;
}

float3 alice_procedural_matcap(float3 normal_view, float3 bl, float3 br, float3 tl, float3 tr) {
    float u = saturate(normal_view.x * 0.5 + 0.5);
    float v = saturate(normal_view.y * 0.5 + 0.5);
    float3 bottom = lerp(bl, br, u);
    float3 top = lerp(tl, tr, u);
    return lerp(bottom, top, v);
}

float alice_stylized_specular(float n_dot_h, float sharpness, float soft_edge) {
    float ndh = saturate(n_dot_h);
    float raw = pow(ndh, max(sharpness, 1.0));
    float s = clamp(soft_edge, 0.0, 0.5);
    if (s < 1e-6) return step(0.5, raw);
    return smoothstep(0.5 - s, 0.5 + s, raw);
}

float alice_vignette(float2 uv, float radius, float softness) {
    float2 d = uv - float2(0.5, 0.5);
    float len = length(d);
    float inner = max(radius, 0.0);
    float outer = max(inner + max(softness, 0.0), inner + 1e-6);
    if (len <= inner) return 1.0;
    if (len >= outer) return 0.0;
    float t = saturate((len - inner) / (outer - inner));
    return 1.0 - (t * t * (3.0 - 2.0 * t));
}

float3 alice_bloom_toon(float3 color, float threshold, float intensity) {
    float m = max(max(color.r, color.g), color.b);
    return (m > threshold) ? color * intensity : float3(0.0, 0.0, 0.0);
}

float alice_puffy_cloud_layer(float noise_sample, float coverage, float softness) {
    float n = saturate(noise_sample);
    float c = saturate(coverage);
    float s = max(softness, 1e-4);
    return saturate((n - (1.0 - c)) / s);
}

float alice_light_shaft_beam(float3 view_dir, float3 to_sun, float density) {
    float3 v = normalize(view_dir + float3(1e-8, 1e-8, 1e-8));
    float3 s = normalize(to_sun + float3(1e-8, 1e-8, 1e-8));
    float cos_theta = max(dot(v, s), 0.0);
    return pow(cos_theta, max(density, 1.0));
}

float alice_impact_flash(float t, float decay, float intensity) {
    if (t < 0.0) return 0.0;
    return intensity * exp(-t / max(decay, 1e-4));
}

float alice_sun_disc(float3 view, float3 to_sun, float radius, float softness) {
    float3 v = normalize(view + float3(1e-8, 1e-8, 1e-8));
    float3 s = normalize(to_sun + float3(1e-8, 1e-8, 1e-8));
    float cos_theta = dot(v, s);
    float r = max(radius, 0.0);
    float soft = max(softness, 0.0);
    float cos_inner = cos(r);
    float cos_outer = cos(r + soft);
    if (cos_theta >= cos_inner) return 1.0;
    if (cos_theta <= cos_outer) return 0.0;
    float denom = max(cos_inner - cos_outer, 1e-6);
    return clamp((cos_theta - cos_outer) / denom, 0.0, 1.0);
}

float3 alice_saturate(float3 color, float factor) {
    float lum = dot(color, float3(0.2126, 0.7152, 0.0722));
    float3 grey = float3(lum, lum, lum);
    return lerp(grey, color, factor);
}

float alice_hatch_lines(float2 uv, float angle_rad, float density, float thickness) {
    float s = sin(angle_rad);
    float c = cos(angle_rad);
    float projected = uv.x * (-s) + uv.y * c;
    float d = max(density, 1e-6);
    float raw = projected * d;
    float phase = raw - floor(raw);
    float dist = abs(phase - 0.5);
    float t = clamp(thickness, 0.0, 0.5);
    return (dist > 0.5 - t) ? 1.0 : 0.0;
}

float3 alice_tonemap_reinhard(float3 color, float exposure) {
    float3 c = color * max(exposure, 0.0);
    return c / (float3(1.0, 1.0, 1.0) + c);
}

float alice_speed_line(float2 uv, float2 focus, float count, float thickness) {
    float2 d = uv - focus;
    if (abs(d.x) < 1e-6 && abs(d.y) < 1e-6) return 0.0;
    if (count <= 0.0) return 0.0;
    float angle = atan2(d.y, d.x);
    float TAU = 6.28318530718;
    float phase_raw = (angle + 3.14159265359) * count / TAU;
    float phase = phase_raw - floor(phase_raw);
    float dist = abs(phase - 0.5);
    float t = clamp(thickness, 0.0, 0.5);
    return (dist > 0.5 - t) ? 1.0 : 0.0;
}
";

// ============================================================================
// Fixed-anchor palette variants (GLSL)
// ============================================================================

/// GLSL palette variants matching `sky_gradient_bands` (3 anchors),
/// `palette_gradient_5`, `time_of_day`, and `season_palette`
pub const NPR_GLSL_PALETTE_HELPERS: &str = r"
// ALICE-SDF NPR palette helpers (GLSL 330+)

vec3 alice_sky_gradient_bands_3(vec3 dir, vec3 c0, vec3 c1, vec3 c2) {
    float t = clamp((dir.y + 1.0) * 0.5, 0.0, 1.0) * 2.0;
    float idx_f = floor(t);
    float frac_ = clamp(t - idx_f, 0.0, 1.0);
    if (idx_f < 0.5) return mix(c0, c1, frac_);
    return mix(c1, c2, frac_);
}

vec3 alice_palette_gradient_5(float t, vec3 c0, vec3 c1, vec3 c2, vec3 c3, vec3 c4) {
    float scaled = clamp(t, 0.0, 1.0) * 4.0;
    float idx_f = floor(scaled);
    float frac_ = clamp(scaled - idx_f, 0.0, 1.0);
    if (idx_f < 0.5) return mix(c0, c1, frac_);
    if (idx_f < 1.5) return mix(c1, c2, frac_);
    if (idx_f < 2.5) return mix(c2, c3, frac_);
    return mix(c3, c4, frac_);
}

vec3 alice_time_of_day(float sun_altitude, vec3 night, vec3 dawn_dusk, vec3 noon) {
    float alt = clamp(sun_altitude, -1.0, 1.0);
    if (alt <= 0.0) return mix(night, dawn_dusk, clamp(alt + 1.0, 0.0, 1.0));
    return mix(dawn_dusk, noon, clamp(alt, 0.0, 1.0));
}

vec3 alice_season_palette(float t, vec3 spring, vec3 summer, vec3 autumn, vec3 winter) {
    float scaled = clamp(t, 0.0, 1.0) * 4.0;
    float idx_f = floor(scaled);
    float frac_ = clamp(scaled - idx_f, 0.0, 1.0);
    if (idx_f < 0.5) return mix(spring, summer, frac_);
    if (idx_f < 1.5) return mix(summer, autumn, frac_);
    if (idx_f < 2.5) return mix(autumn, winter, frac_);
    return mix(winter, spring, frac_);
}

vec3 alice_palette_gradient_3(float t, vec3 c0, vec3 c1, vec3 c2) {
    float scaled = clamp(t, 0.0, 1.0) * 2.0;
    float idx_f = floor(scaled);
    float frac_ = clamp(scaled - idx_f, 0.0, 1.0);
    if (idx_f < 0.5) return mix(c0, c1, frac_);
    return mix(c1, c2, frac_);
}
";

// ============================================================================
// Fixed-anchor palette variants (WGSL)
// ============================================================================

/// WGSL palette variants matching the GLSL set
pub const NPR_WGSL_PALETTE_HELPERS: &str = r"
// ALICE-SDF NPR palette helpers (WGSL)

fn alice_sky_gradient_bands_3(dir: vec3<f32>, c0: vec3<f32>, c1: vec3<f32>, c2: vec3<f32>) -> vec3<f32> {
    let t = clamp((dir.y + 1.0) * 0.5, 0.0, 1.0) * 2.0;
    let idx_f = floor(t);
    let frac_val = clamp(t - idx_f, 0.0, 1.0);
    if (idx_f < 0.5) { return mix(c0, c1, vec3<f32>(frac_val)); }
    return mix(c1, c2, vec3<f32>(frac_val));
}

fn alice_palette_gradient_5(
    t: f32,
    c0: vec3<f32>, c1: vec3<f32>, c2: vec3<f32>, c3: vec3<f32>, c4: vec3<f32>,
) -> vec3<f32> {
    let scaled = clamp(t, 0.0, 1.0) * 4.0;
    let idx_f = floor(scaled);
    let frac_val = clamp(scaled - idx_f, 0.0, 1.0);
    if (idx_f < 0.5) { return mix(c0, c1, vec3<f32>(frac_val)); }
    if (idx_f < 1.5) { return mix(c1, c2, vec3<f32>(frac_val)); }
    if (idx_f < 2.5) { return mix(c2, c3, vec3<f32>(frac_val)); }
    return mix(c3, c4, vec3<f32>(frac_val));
}

fn alice_time_of_day(sun_altitude: f32, night: vec3<f32>, dawn_dusk: vec3<f32>, noon: vec3<f32>) -> vec3<f32> {
    let alt = clamp(sun_altitude, -1.0, 1.0);
    if (alt <= 0.0) { return mix(night, dawn_dusk, vec3<f32>(clamp(alt + 1.0, 0.0, 1.0))); }
    return mix(dawn_dusk, noon, vec3<f32>(clamp(alt, 0.0, 1.0)));
}

fn alice_season_palette(
    t: f32,
    spring: vec3<f32>, summer: vec3<f32>, autumn: vec3<f32>, winter: vec3<f32>,
) -> vec3<f32> {
    let scaled = clamp(t, 0.0, 1.0) * 4.0;
    let idx_f = floor(scaled);
    let frac_val = clamp(scaled - idx_f, 0.0, 1.0);
    if (idx_f < 0.5) { return mix(spring, summer, vec3<f32>(frac_val)); }
    if (idx_f < 1.5) { return mix(summer, autumn, vec3<f32>(frac_val)); }
    if (idx_f < 2.5) { return mix(autumn, winter, vec3<f32>(frac_val)); }
    return mix(winter, spring, vec3<f32>(frac_val));
}

fn alice_palette_gradient_3(t: f32, c0: vec3<f32>, c1: vec3<f32>, c2: vec3<f32>) -> vec3<f32> {
    let scaled = clamp(t, 0.0, 1.0) * 2.0;
    let idx_f = floor(scaled);
    let frac_val = clamp(scaled - idx_f, 0.0, 1.0);
    if (idx_f < 0.5) { return mix(c0, c1, vec3<f32>(frac_val)); }
    return mix(c1, c2, vec3<f32>(frac_val));
}
";

// ============================================================================
// Fixed-anchor palette variants (HLSL)
// ============================================================================

/// HLSL palette variants matching the GLSL set
pub const NPR_HLSL_PALETTE_HELPERS: &str = r"
// ALICE-SDF NPR palette helpers (HLSL SM 5.0+)

float3 alice_sky_gradient_bands_3(float3 dir, float3 c0, float3 c1, float3 c2) {
    float t = saturate((dir.y + 1.0) * 0.5) * 2.0;
    float idx_f = floor(t);
    float frac_val = saturate(t - idx_f);
    if (idx_f < 0.5) return lerp(c0, c1, frac_val);
    return lerp(c1, c2, frac_val);
}

float3 alice_palette_gradient_5(float t, float3 c0, float3 c1, float3 c2, float3 c3, float3 c4) {
    float scaled = saturate(t) * 4.0;
    float idx_f = floor(scaled);
    float frac_val = saturate(scaled - idx_f);
    if (idx_f < 0.5) return lerp(c0, c1, frac_val);
    if (idx_f < 1.5) return lerp(c1, c2, frac_val);
    if (idx_f < 2.5) return lerp(c2, c3, frac_val);
    return lerp(c3, c4, frac_val);
}

float3 alice_time_of_day(float sun_altitude, float3 night, float3 dawn_dusk, float3 noon) {
    float alt = clamp(sun_altitude, -1.0, 1.0);
    if (alt <= 0.0) return lerp(night, dawn_dusk, saturate(alt + 1.0));
    return lerp(dawn_dusk, noon, saturate(alt));
}

float3 alice_season_palette(float t, float3 spring, float3 summer, float3 autumn, float3 winter) {
    float scaled = saturate(t) * 4.0;
    float idx_f = floor(scaled);
    float frac_val = saturate(scaled - idx_f);
    if (idx_f < 0.5) return lerp(spring, summer, frac_val);
    if (idx_f < 1.5) return lerp(summer, autumn, frac_val);
    if (idx_f < 2.5) return lerp(autumn, winter, frac_val);
    return lerp(winter, spring, frac_val);
}

float3 alice_palette_gradient_3(float t, float3 c0, float3 c1, float3 c2) {
    float scaled = saturate(t) * 2.0;
    float idx_f = floor(scaled);
    float frac_val = saturate(scaled - idx_f);
    if (idx_f < 0.5) return lerp(c0, c1, frac_val);
    return lerp(c1, c2, frac_val);
}
";

/// Return the helper snippet for the requested shader language
#[must_use]
pub const fn helpers_for(language: ShaderLanguage) -> &'static str {
    match language {
        ShaderLanguage::Glsl => NPR_GLSL_HELPERS,
        ShaderLanguage::Wgsl => NPR_WGSL_HELPERS,
        ShaderLanguage::Hlsl => NPR_HLSL_HELPERS,
    }
}

/// Return the palette helper snippet for the requested shader language
#[must_use]
pub const fn palette_helpers_for(language: ShaderLanguage) -> &'static str {
    match language {
        ShaderLanguage::Glsl => NPR_GLSL_PALETTE_HELPERS,
        ShaderLanguage::Wgsl => NPR_WGSL_PALETTE_HELPERS,
        ShaderLanguage::Hlsl => NPR_HLSL_PALETTE_HELPERS,
    }
}

/// Concatenate core + palette helpers for a language into an owned String
#[must_use]
pub fn full_helpers_for(language: ShaderLanguage) -> String {
    format!("{}{}", helpers_for(language), palette_helpers_for(language))
}

/// Selector for the shader language dispatched by [`helpers_for`]
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ShaderLanguage {
    /// OpenGL / Vulkan Shading Language 330+
    Glsl,
    /// WebGPU Shading Language
    Wgsl,
    /// Direct3D High-Level Shading Language 5.0+
    Hlsl,
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn glsl_helpers_have_expected_functions() {
        for name in [
            "alice_toon_ramp",
            "alice_soft_toon_ramp",
            "alice_two_tone",
            "alice_posterize_color",
            "alice_distance_field_outline",
            "alice_distance_field_outline_soft",
            "alice_fresnel_rim",
            "alice_procedural_matcap",
            "alice_stylized_specular",
            "alice_vignette",
            "alice_bloom_toon",
            "alice_puffy_cloud_layer",
            "alice_light_shaft_beam",
            "alice_impact_flash",
            "alice_sun_disc",
            "alice_saturate",
            "alice_hatch_lines",
            "alice_tonemap_reinhard",
            "alice_speed_line",
        ] {
            assert!(
                NPR_GLSL_HELPERS.contains(name),
                "missing GLSL helper: {name}"
            );
            assert!(
                NPR_WGSL_HELPERS.contains(name),
                "missing WGSL helper: {name}"
            );
            assert!(
                NPR_HLSL_HELPERS.contains(name),
                "missing HLSL helper: {name}"
            );
        }
    }

    #[test]
    fn helpers_for_dispatch_returns_expected_source() {
        assert_eq!(helpers_for(ShaderLanguage::Glsl), NPR_GLSL_HELPERS);
        assert_eq!(helpers_for(ShaderLanguage::Wgsl), NPR_WGSL_HELPERS);
        assert_eq!(helpers_for(ShaderLanguage::Hlsl), NPR_HLSL_HELPERS);
    }

    #[test]
    fn snippets_are_nontrivial() {
        assert!(NPR_GLSL_HELPERS.len() > 200);
        assert!(NPR_WGSL_HELPERS.len() > 200);
        assert!(NPR_HLSL_HELPERS.len() > 200);
    }

    #[test]
    fn palette_helpers_have_expected_functions() {
        for name in [
            "alice_sky_gradient_bands_3",
            "alice_palette_gradient_5",
            "alice_time_of_day",
            "alice_season_palette",
            "alice_palette_gradient_3",
        ] {
            assert!(
                NPR_GLSL_PALETTE_HELPERS.contains(name),
                "missing GLSL palette: {name}"
            );
            assert!(
                NPR_WGSL_PALETTE_HELPERS.contains(name),
                "missing WGSL palette: {name}"
            );
            assert!(
                NPR_HLSL_PALETTE_HELPERS.contains(name),
                "missing HLSL palette: {name}"
            );
        }
    }

    #[test]
    fn palette_helpers_for_dispatch_returns_expected_source() {
        assert_eq!(
            palette_helpers_for(ShaderLanguage::Glsl),
            NPR_GLSL_PALETTE_HELPERS
        );
        assert_eq!(
            palette_helpers_for(ShaderLanguage::Wgsl),
            NPR_WGSL_PALETTE_HELPERS
        );
        assert_eq!(
            palette_helpers_for(ShaderLanguage::Hlsl),
            NPR_HLSL_PALETTE_HELPERS
        );
    }

    #[test]
    fn full_helpers_concatenates_core_and_palette() {
        let full = full_helpers_for(ShaderLanguage::Glsl);
        assert!(full.contains("alice_toon_ramp"));
        assert!(full.contains("alice_sky_gradient_bands_3"));
        assert!(full.contains("alice_season_palette"));
    }
}