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// Common functions for Signed Distance Field (SDF) raymarching.
// These functions require the user to define a `df(vec3<f32>) -> f32` function
// which represents the scene's distance field.
const TOLERANCE: f32 = 0.0005;
const MAX_RAY_LENGTH: f32 = 20.0;
const MAX_RAY_MARCHES: i32 = 80;
const NORM_OFF: f32 = 0.005;
// Computes the surface normal of the distance field at a point `pos`.
fn normal(pos: vec3<f32>) -> vec3<f32> {
let eps = vec2<f32>(NORM_OFF, 0.0);
var nor: vec3<f32>;
nor.x = df(pos + eps.xyy) - df(pos - eps.xyy);
nor.y = df(pos + eps.yxy) - df(pos - eps.yxy);
nor.z = df(pos + eps.yyx) - df(pos - eps.yyx);
return normalize(nor);
}
// Performs the raymarching operation.
// Returns the distance along the ray to the surface, or MAX_RAY_LENGTH if no surface is hit.
fn rayMarch(ro: vec3<f32>, rd: vec3<f32>, initt: f32) -> f32 {
var t = initt;
for (var i = 0; i < MAX_RAY_MARCHES; i++) {
if (t > MAX_RAY_LENGTH) {
t = MAX_RAY_LENGTH;
break;
}
let d = df(ro + rd * t);
if (d < TOLERANCE) {
break;
}
t += d;
}
return t;
}
// Computes a soft shadow for a given point.
fn shadow(lp: vec3<f32>, ld: vec3<f32>, mint: f32, maxt: f32) -> f32 {
let ds = 1.0 - 0.4;
var t = mint;
var nd = 1e6;
let soff = 0.05;
let smul = 1.5;
let MAX_SHD_MARCHES = 20;
for (var i = 0; i < MAX_SHD_MARCHES; i++) {
let p = lp + ld * t;
let d = df(p);
if (d < TOLERANCE || t >= maxt) {
let sd = 1.0 - exp(-smul * max(t / maxt - soff, 0.0));
return select(mix(sd, 1.0, smoothstep(0.0, 0.025, nd)), sd, t >= maxt);
}
nd = min(nd, d);
t += ds * d;
}
let sd = 1.0 - exp(-smul * max(t / maxt - soff, 0.0));
return sd;
}
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