AccelerationStructureInstance

struct

Core/Vixen.Graphics/AccelerationStructures.cs:109

csharp

public struct AccelerationStructureInstance

One placed reference to a bottom-level structure, in the layout every API shares.

No guide page documents this yet — the page shows what the code says about itself.

Remarks

Sixty-four bytes, bit for bit VkAccelerationStructureInstanceKHR (and D3D12's D3D12_RAYTRACING_INSTANCE_DESC, which is the same layout — the vendors agreed for once): a 3×4 row-major world transform, a 24-bit custom index with an 8-bit visibility mask, a 24-bit hit-group offset with 8 flag bits, and the bottom-level structure's GPU address from GetAccelerationStructureAddress.

The transform's rows are the upper three rows of a column-vector matrix — each row is (basis.X, basis.Y, basis.Z, translation) for one world axis. Row-vector Matrix4x4 users transpose on the way in; FromRows spells the layout so the transposition happens in exactly one place.

Fields and properties (15)

public float R0X
Row zero of the transform: world X from object space, then X translation.
public float R0Y
Row zero of the transform: world X from object space, then X translation.
public float R0Z
Row zero of the transform: world X from object space, then X translation.
public float R0W
Row zero of the transform: world X from object space, then X translation.
public float R1X
Row one: world Y.
public float R1Y
Row one: world Y.
public float R1Z
Row one: world Y.
public float R1W
Row one: world Y.
public float R2X
Row two: world Z.
public float R2Y
Row two: world Z.
public float R2Z
Row two: world Z.
public float R2W
Row two: world Z.
public uint IndexAndMask
Low 24 bits: the custom index a shader reads back. High 8: the visibility mask — zero is invisible to every ray.
public uint OffsetAndFlags
Low 24 bits: the hit-group offset (zero for ray queries). High 8: instance flags — zero is the default, and the queries here disable culling per query anyway.
public ulong BottomLevel
The bottom-level structure's GPU address.

Methods (2)

public static AccelerationStructureInstance Identity(ulong bottomLevel, int index = 0)
An identity-placed, fully visible instance of one bottom-level structure.
public static AccelerationStructureInstance FromRows(ulong bottomLevel, ReadOnlySpan<float> rows, int index = 0)
The transform from three explicit rows, each (basis, translation) for one world axis.

Used by (1)

AccelerationStructureDeviceTestsVixen.Graphics.Golden.Tests