RenderTargetArrayIndex in D3D12_VIEW_INSTANCE_LOCATION mismatched with effective SV_RenderTargetArrayIndex

Gaming and Visualization Technologies APIs DirectX, DXR, DirectCompute
1

Hello, I met some trouble while working with view instancing in d3d12.

Create PSO with D3D12_VIEW_INSTANCING_DESC, such as below

ViewInstanceCount = 4,
pViewInstanceLocations = {
    {ViewportArrayIndex=0, RenderTargetArrayIndex=0},
    {0, 1},
    {0, 2},
    {0, 3},
}

and set render target array that has 4 slices.

Each slice has rendered, but the order is not correct.

I’ve checked if a variable of SV_ViewID is equal to another variable of SV_RenderTargetArrayIndex, and those are not equal some cases.

  • 0 (ViewID), 0 (RenderTargetArrayIndex )
  • 1, 3 → Different
  • 2, 2
  • 3, 1 → Different

If ViewInstanceCount is 3 and Locations are {0, 0}, {0, 1}, and {0, 2}, then SV_RenderTargetArrayIndex is each given as 0, 2, 1.

Also I tried with both SV_ViewportArrayIndex and SV_RenderTargetArrayIndex,

ViewInstanceCount = 4,
pViewInstanceLocations = {
    {ViewportArrayIndex=0, RenderTargetArrayIndex=0},
    {1, 1},
    {2, 2},
    {3, 3},
}

The result of SV_RenderTargetArrayIndex is still wiered, but the SV_ViewportArrayIndex is equal with SV_ViewID as I set.

  • 0 (ViewID), 0 (ViewportArrayIndex), 0 (RenderTargetArrayIndex)
  • 1, 1, 3 → Different
  • 2, 2, 2
  • 3, 3, 1 → Different

So I set the RenderTargetArrayIndex such as below, and finally get an increasing order of RenderTargetArrayIndex.

ViewInstanceCount = 4,
pViewInstanceLocations = {
    {ViewportArrayIndex=0, RenderTargetArrayIndex=0},
    {0, 3},
    {0, 2},
    {0, 1},
}

However, can’t find proper description why I should code such that.

2

Note that.
When I create PSO with fixed RenderTargetArrayIndex=0 for each pViewInstanceLocations[0~3] to set SV_RenderTargetArrayIndex dynamically in pre-rasterizer shaders, it works well as I want.