33 lines
1.3 KiB
WebGPU Shading Language
33 lines
1.3 KiB
WebGPU Shading Language
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// RTVolume intersection shader (runs in TRACE, per AABB the ray enters).
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// Analytic ray-sphere test: the unit box [-1,1]^3 is treated as the
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// bounding volume of a sphere of radius 1 centred at the box centre. The
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// ray is in object space and is NOT normalised (it is worldToObject *
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// worldRay), so the returned t is directly comparable to the world-space
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// ray parameter the tracer commits — solve the quadratic with the general
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// a = dot(d,d) form rather than assuming |d| == 1.
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fn intersection_main(ray: RayDesc, aabbMin: vec3<f32>, aabbMax: vec3<f32>,
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primitiveId: u32) -> IntersectionResult {
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var r: IntersectionResult;
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r.hit = false;
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let center = (aabbMin + aabbMax) * 0.5;
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let radius = (aabbMax.x - aabbMin.x) * 0.5;
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let oc = ray.origin - center;
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let a = dot(ray.direction, ray.direction);
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let b = 2.0 * dot(oc, ray.direction);
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let c = dot(oc, oc) - radius * radius;
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let disc = b * b - 4.0 * a * c;
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if (disc < 0.0) { return r; }
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let sq = sqrt(disc);
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var t = (-b - sq) / (2.0 * a); // near root
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if (t < ray.tMin) { t = (-b + sq) / (2.0 * a); } // fall back to far root
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if (t < ray.tMin || t > ray.tMax) { return r; }
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r.hit = true;
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r.t = t;
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r.attribs = vec2<f32>(0.0);
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r.hitKind = 0u;
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return r;
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}
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