I’ve been experimenting with Bindless rendering using DirectX12 & Vulkan APIs recently.

Here is the layout I currently use for bindless table :

Table Layout

Type	Range	Space	Binding
Texture1D (float4)	[0 ..16383]	10	0
Texture2D (float4)	[0 ..16383]	20	0
Texture2D (uint)	[0 ..16383]	21	0
Texture3D (float4)	[0 ..16383]	30	0
ByteAddressBuffer	[16384..32767]	-	1
RWTexture1D	[32768..40959]	210	2
RWTexture2D	[32768..40959]	220	2
RWTexture3D	[32768..40959]	230	2
RWByteAddressBuffer	[40960..49151]	200	3
RaytracingAccelerationStructure	[49152..49167]	-	4

Notes:

• The DirectX12 version uses the Space value to alias the different types of resource view formats
• The Vulkan version uses the Binding value to differenciate between the different types of resource views
• Several TLAS can be used if multiple views are used. The current value implies a maximum of 16 views using RayTracing.

In case you want more details, check the file table.hlsi in the repo.

Reserved Slots

By default, a new resource requiring a view will be created allocating a new bindless handle in these ranges, but it’s convenient to have some hard-coded slots :

• To avoid an extra indirection (e.g. passing buffer handle as root constant) :

PS_Output PS_Forward(VS_Output _input)
{
    PS_Output output = (PS_Output)0;
    
    ViewConstants viewConstants;
    viewConstants.Load(getBuffer(RESERVEDSLOT_BUFSRV_VIEWCONSTANTS));

    [...]

• To fallback to missing texture :

m_defaultTexture = device->createTexture(texDesc, "DefaultTex2D", initData, ReservedSlot(BINDLESS_TEXTURE_INVALID));
VG_ASSERT(m_defaultTexture->getTextureHandle() == BINDLESS_TEXTURE_INVALID);
        
// copy descriptor to all 'texture' slots
for (uint i = BINDLESS_TEXTURE_START; i < BINDLESS_TEXTURE_COUNT; ++i)
    if (BINDLESS_TEXTURE_INVALID != i)
        copyTextureHandle(i, m_defaultTexture);

• To initialize shader structs with proper default values (e.g. default albedo, default normal map etc…) :

struct GPUMaterialData
{
    #ifdef __cplusplus
    GPUMaterialData()
    {
        setAlbedoTextureHandle(RESERVEDSLOT_TEXSRV_DEFAULT_ALBEDO);
        setNormalTextureHandle(RESERVEDSLOT_TEXSRV_DEFAULT_NORMAL);
        setPBRTextureHandle(RESERVEDSLOT_TEXSRV_DEFAULT_PBR);
    }   
    #endif 

    // .x = albedo | normal 
    // .y = pbr | unused 
    uint4 textures; 

    [...]
};

These custom hardcoded slots are defined compile-time and “allocated” bottom-up before the last value of the range used as invalid value.

Type	Name	Value
Texture	PBR	16379
Texture	Normal	16380
Texture	Albedo	16381
Texture	ImGui	16382
Texture	Default	16383
Buffer	InstanceData	32763
Buffer	SkinningMatrices	32764
Buffer	LightsConstants	32765
Buffer	ViewConstants	32766
Buffer	Default	32767

Debugging

Using GPU debug tools like Renderdoc or PIX, it is possible to view the descriptor used and the resource contents.