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docs(webgpu-rt): add RTVolume example (procedural spheres + any-hit cut-out)

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A 3x3x3 grid of AABB-geometry spheres rendered through an analytic
ray-sphere intersection shader, with an any-hit spherical-checkerboard
cut-out so the background shows through. Exercises both features end to
end on the WebGPU wavefront tracer.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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catbot 2026-06-02 22:09:30 +00:00
commit 5dd1086f08
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// RTVolume — procedural (AABB) ray tracing on the WebGPU wavefront tracer.
// Demonstrates the two features this example was written to exercise:
//
// * VK_GEOMETRY_TYPE_AABBS_KHR equivalent — a BLAS built from AABBs
// (Mesh::BuildProcedural) whose surface is supplied by an intersection
// shader (here an analytic ray–sphere test). The boxes are unit cubes
// [-1,1]^3; the intersection shader turns each into a sphere.
//
// * any-hit — the spheres are registered non-opaque, and an any-hit
// shader punches a spherical checkerboard of holes by returning
// RT_ANYHIT_IGNORE for half the cells. Without any-hit the spheres are
// solid; with it you can see the background (and other spheres)
// through the cut-out cells.
//
// A 3×3×3 grid of these procedural spheres is shaded by surface normal +
// a fixed sun. WebGPU/DOM only — this is the software RT path.
#ifndef CRAFTER_GRAPHICS_WINDOW_DOM
int main() { return 0; } // native path is hardware RT; out of scope here
#else
import Crafter.Graphics;
import Crafter.Math;
import Crafter.Event;
import std;
using namespace Crafter;
namespace fs = std::filesystem;
namespace {
constexpr int kGrid = 3;
constexpr float kSpacing = 3.0f;
struct CameraGPU {
float origin[3]; float pad0;
float right[3]; float tanHalf;
float up[3]; float aspect;
float forward[3]; float pad1;
};
static_assert(sizeof(CameraGPU) == 64);
}
int main() {
const int instanceCount = kGrid * kGrid * kGrid;
std::println("[RTVolume] grid {}^3 = {} procedural spheres", kGrid, instanceCount);
Device::Initialize();
static Window window(1280, 720, "RTVolume");
auto cmd = window.StartInit();
DescriptorHeapWebGPU heap;
heap.Initialize(/*images*/ 1, /*buffers*/ 2, /*samplers*/ 1);
// SBT order fixes the shader indices used by the groups below.
std::array<WebGPUShader, 6> shaders {{
WebGPUShader(fs::path("raygen.wgsl"), "raygen_main", WebGPURTStage::Raygen),
WebGPUShader(fs::path("miss.wgsl"), "miss_main", WebGPURTStage::Miss),
WebGPUShader(fs::path("closesthit.wgsl"), "closesthit_main", WebGPURTStage::ClosestHit),
WebGPUShader(fs::path("anyhit.wgsl"), "anyhit_main", WebGPURTStage::AnyHit),
WebGPUShader(fs::path("intersection.wgsl"), "intersection_main", WebGPURTStage::Intersection),
WebGPUShader(fs::path("resolve.wgsl"), "resolve_main", WebGPURTStage::Resolve),
}};
ShaderBindingTableWebGPU sbt;
sbt.Init(shaders);
std::array<RTShaderGroup, 1> raygenGroups {{ { .type = RTShaderGroupType::General, .generalShader = 0 } }};
std::array<RTShaderGroup, 1> missGroups {{ { .type = RTShaderGroupType::General, .generalShader = 1 } }};
// One procedural hit group: closest-hit + any-hit + intersection.
std::array<RTShaderGroup, 1> hitGroups {{ {
.type = RTShaderGroupType::ProceduralHitGroup,
.closestHitShader = 2,
.anyHitShader = 3,
.intersectionShader = 4,
} }};
std::array<UICustomBinding, 1> bindings {{
{ .group = 3, .binding = 0, .kind = UICustomBindingKind::Buffer, ._pad = 0, .pushOffset = 0 },
}};
PipelineRTWebGPU pipeline;
pipeline.Init(cmd, raygenGroups, missGroups, hitGroups, sbt, bindings);
// ── One procedural unit-box BLAS. The intersection shader treats the
// box as the bounding volume of a radius-1 sphere centred at the
// object origin. opaque=false so the any-hit cut-out runs. ─────────
static std::array<RTAabb, 1> boxes {{
{ .min = {-1.0f, -1.0f, -1.0f}, .max = {1.0f, 1.0f, 1.0f} },
}};
static Mesh sphere;
sphere.BuildProcedural(boxes, /*opaque*/ false, cmd);
// ── Camera buffer + handle array. ─────────────────────────────────
WebGPUBuffer<CameraGPU, true> cameraBuf;
cameraBuf.Create(1);
static std::array<std::uint32_t, 1> userHandles { cameraBuf.handle };
// ── Instance grid. ────────────────────────────────────────────────
static std::vector<RenderingElement3D> renderers;
renderers.reserve(static_cast<std::size_t>(instanceCount));
const float origin0 = -0.5f * static_cast<float>(kGrid - 1) * kSpacing;
for (int x = 0; x < kGrid; ++x)
for (int y = 0; y < kGrid; ++y)
for (int z = 0; z < kGrid; ++z) {
renderers.emplace_back();
RenderingElement3D& r = renderers.back();
auto& tx = r.instance.transform.matrix;
tx[0][0] = 1; tx[0][1] = 0; tx[0][2] = 0; tx[0][3] = origin0 + float(x) * kSpacing;
tx[1][0] = 0; tx[1][1] = 1; tx[1][2] = 0; tx[1][3] = origin0 + float(y) * kSpacing;
tx[2][0] = 0; tx[2][1] = 0; tx[2][2] = 1; tx[2][3] = origin0 + float(z) * kSpacing;
r.instance.instanceCustomIndex = static_cast<std::uint32_t>(renderers.size() - 1);
r.instance.mask = 0xFF;
r.instance.instanceShaderBindingTableRecordOffset = 0;
// flags = 0: do NOT force opaque, so the any-hit shader runs.
r.instance.flags = 0;
r.instance.accelerationStructureReference = sphere.blasAddr;
RenderingElement3D::Add(&r);
}
RenderingElement3D::BuildTLAS(cmd, 0);
window.descriptorHeap = &heap;
window.FinishInit();
RTPass rtPass(&pipeline);
rtPass.handlesPtr = userHandles.data();
rtPass.handlesCount = static_cast<std::uint32_t>(userHandles.size());
rtPass.maxDepth = 1; // primary only
window.passes.push_back(&rtPass);
// ── Free camera framing the grid. ─────────────────────────────────
const float ext = float(kGrid - 1) * kSpacing;
struct CamState {
Vector<float, 3, 4> position;
float yaw;
float pitch;
} cam {
Vector<float, 3, 4>{ ext * 1.1f, ext * 0.8f, ext * 1.6f },
0.0f, 0.0f,
};
{
Vector<float, 3, 4> d { -cam.position.x, -cam.position.y, -cam.position.z };
const float len = std::sqrt(d.x*d.x + d.y*d.y + d.z*d.z);
cam.yaw = std::atan2(d.z, d.x);
cam.pitch = std::asin(d.y / len);
}
Input::Map inputMap;
Input::Action& moveAct = inputMap.AddAction("Move", Input::ActionType::Vector2);
Input::Action& lookAct = inputMap.AddAction("Look", Input::ActionType::Vector2);
moveAct.bindings = { Input::WASDBind{
Key(CrafterKeys::W), Key(CrafterKeys::S), Key(CrafterKeys::A), Key(CrafterKeys::D) } };
lookAct.bindings = { Input::MouseDeltaBind{ 1.0f } };
inputMap.Attach(window);
const float kMoveSpeed = ext * 0.8f + 1.0f;
const float kLookSens = 0.05f;
const float kDt = 1.0f / 60.0f;
EventListener<void> camTick(&window.onBeforeUpdate, [&]() {
inputMap.Tick();
cam.yaw += lookAct.vector2.x * kLookSens;
cam.pitch -= lookAct.vector2.y * kLookSens;
cam.pitch = std::clamp(cam.pitch, -1.55f, 1.55f);
const float cp = std::cos(cam.pitch), sp = std::sin(cam.pitch);
const float cy = std::cos(cam.yaw), sy = std::sin(cam.yaw);
Vector<float, 3, 4> forward { cp * cy, sp, cp * sy };
Vector<float, 3, 4> worldUp { 0.0f, 1.0f, 0.0f };
Vector<float, 3, 4> right { forward.y*worldUp.z - forward.z*worldUp.y,
forward.z*worldUp.x - forward.x*worldUp.z,
forward.x*worldUp.y - forward.y*worldUp.x };
const float rLen = std::sqrt(right.x*right.x + right.y*right.y + right.z*right.z);
right.x /= rLen; right.y /= rLen; right.z /= rLen;
Vector<float, 3, 4> up { right.y*forward.z - right.z*forward.y,
right.z*forward.x - right.x*forward.z,
right.x*forward.y - right.y*forward.x };
const float dx = moveAct.vector2.x * kMoveSpeed * kDt;
const float dy = moveAct.vector2.y * kMoveSpeed * kDt;
cam.position.x += right.x*dx + forward.x*dy;
cam.position.y += right.y*dx + forward.y*dy;
cam.position.z += right.z*dx + forward.z*dy;
CameraGPU& g = cameraBuf.value[0];
g.origin[0]=cam.position.x; g.origin[1]=cam.position.y; g.origin[2]=cam.position.z; g.pad0=0;
g.right[0]=right.x; g.right[1]=right.y; g.right[2]=right.z;
g.up[0]=up.x; g.up[1]=up.y; g.up[2]=up.z;
g.forward[0]=forward.x; g.forward[1]=forward.y; g.forward[2]=forward.z;
g.aspect = float(window.width) / float(window.height);
g.tanHalf = std::tan(70.0f * 3.14159265f / 360.0f);
g.pad1 = 0;
cameraBuf.FlushDevice();
});
window.Render();
window.StartUpdate();
window.StartSync();
return 0;
}
#endif