52 lines
2.7 KiB
Markdown
52 lines
2.7 KiB
Markdown
|
# Create an acceleration structure
|
||
|
|
[`IRayTracingAccelStruct`](xref:UnityEngine.Rendering.UnifiedRayTracing.IRayTracingAccelStruct) is the data structure used to represent a collection of instances and geometries that are used for GPU ray tracing.
|
||
|
|
|
||
|
|
Create an acceleration structure with the following code:
|
||
|
|
```C#
|
||
|
|
var options = new AccelerationStructureOptions();
|
||
|
|
IRayTracingAccelStruct rtAccelStruct = rtContext.CreateAccelerationStructure(options);
|
||
|
|
```
|
||
|
|
|
||
|
|
## Build options
|
||
|
|
[`AccelerationStructureOptions`](xref:UnityEngine.Rendering.UnifiedRayTracing.AccelerationStructureOptions) allows you to configure the build algorithm. The trade-off is as follows: A faster build results in worse ray tracing performance, and conversely, a slower build can improve ray tracing performance.
|
||
|
|
|
||
|
|
The following fields can be configured:
|
||
|
|
|
||
|
|
|Field|Description|
|
||
|
|
|-|-|
|
||
|
|
|`buildFlags`|Adjust the buildFlags to prioritize either faster construction of the acceleration structure or faster ray tracing.|
|
||
|
|
|`useCPUBuild` (Compute backend)|When set to true, Unity builds the acceleration structure on the CPU instead of the GPU. This option has no effect when using the `Hardware` backend. CPU-based builds use a more advanced algorithm, resulting in a higher-quality acceleration structure, which enhances overall ray tracing performance.|
|
||
|
|
|
||
|
|
The following example demonstrates how to get the best ray tracing performance. These options make the acceleration structure longer to build, however.
|
||
|
|
```HLSL
|
||
|
|
var options = new AccelerationStructureOptions() {
|
||
|
|
buildFlags = BuildFlags.PreferFastTrace,
|
||
|
|
useCPUBuild = true
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
## Populate the acceleration structure
|
||
|
|
Unlike [`RayTracingAccelerationStructure`](xref:UnityEngine.Rendering.RayTracingAccelerationStructure), there is no support for automatic synchronization between the acceleration structure's instances and the scene instances. You need to add them manually, for example:
|
||
|
|
```C#
|
||
|
|
var instanceDesc = new MeshInstanceDesc(mesh, 0 /*subMeshIndex*/);
|
||
|
|
instanceDesc.localToWorldMatrix = /* desired transform */;
|
||
|
|
rtAccelStruct.AddInstance(instanceDesc);
|
||
|
|
```
|
||
|
|
|
||
|
|
To trace rays against all the Mesh-based GameObjects in your scene, add them to the [`IRayTracingAccelStruct`](xref:UnityEngine.Rendering.UnifiedRayTracing.IRayTracingAccelStruct). For example:
|
||
|
|
```C#
|
||
|
|
var meshRenderers = UnityEngine.Object.FindObjectsByType<MeshRenderer>(FindObjectsSortMode.None);
|
||
|
|
foreach (var renderer in meshRenderers)
|
||
|
|
{
|
||
|
|
var mesh = renderer.GetComponent<MeshFilter>().sharedMesh;
|
||
|
|
int subMeshCount = mesh.subMeshCount;
|
||
|
|
|
||
|
|
for (int i = 0; i < subMeshCount; ++i)
|
||
|
|
{
|
||
|
|
var instanceDesc = new MeshInstanceDesc(mesh, i);
|
||
|
|
instanceDesc.localToWorldMatrix = renderer.transform.localToWorldMatrix;
|
||
|
|
rtAccelStruct.AddInstance(instanceDesc);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
```
|