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Graphics: (d3d12 pt II) SRV descriptor slot allocator #213

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Graphics: (d3d12 pt II) SRV descriptor slot allocator #213

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68 changes: 67 additions & 1 deletion code/framework/src/graphics/backend/d3d12.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -41,12 +41,22 @@ namespace Framework::Graphics {
{
D3D12_DESCRIPTOR_HEAP_DESC desc {};
desc.Type = D3D12_DESCRIPTOR_HEAP_TYPE_CBV_SRV_UAV;
desc.NumDescriptors = _frameBufferCount;
desc.NumDescriptors = _frameBufferCount + kExtraSrvSlots;
desc.Flags = D3D12_DESCRIPTOR_HEAP_FLAG_SHADER_VISIBLE;

if (pD3DDevice->CreateDescriptorHeap(&desc, IID_PPV_ARGS(&_srvHeap)) != S_OK) {
return false;
}

// Manage slots that are not reserved for ImGui and headroom
_srvDescriptorSize = pD3DDevice->GetDescriptorHandleIncrementSize(D3D12_DESCRIPTOR_HEAP_TYPE_CBV_SRV_UAV);
_srvHeapSize = desc.NumDescriptors;
_srvSlotInUse.assign(_srvHeapSize, false);
_freeSrvSlots.clear();
const auto extraSrvStart = _frameBufferCount - 1;
for (UINT i = kExtraSrvSlots; i > 0; i--) {
_freeSrvSlots.push_back(extraSrvStart + i);
}
}

// #3 create rtv heap
Expand Down Expand Up @@ -99,6 +109,7 @@ namespace Framework::Graphics {
// release objects
_rtvHeap->Release();
_srvHeap->Release();
_srvHeap = nullptr;
_commandList->Release();
for (const auto &frameContext : _frameContext) {
frameContext._commandAllocator->Release();
Expand Down Expand Up @@ -140,4 +151,59 @@ namespace Framework::Graphics {
int D3D12Backend::NumFramesInFlight() const {
return _frameBufferCount;
}

int D3D12Backend::AllocateSRVSlot() {
std::lock_guard<std::mutex> lock(_srvMutex);
if (!_srvHeap) {
Framework::Logging::GetLogger(FRAMEWORK_INNER_GRAPHICS)->error("D3D12Backend::AllocateSRVSlot, no descriptor heap");
return -1;
}
if (_freeSrvSlots.empty()) {
Framework::Logging::GetLogger(FRAMEWORK_INNER_GRAPHICS)->error("D3D12Backend::AllocateSRVSlot, heap exhausted");
return -1;
}
const auto slot = _freeSrvSlots.back();
_freeSrvSlots.pop_back();
_srvSlotInUse[slot] = true;
return static_cast<int>(slot);
}

void D3D12Backend::FreeSRVSlot(int slot) {
std::lock_guard<std::mutex> lock(_srvMutex);
// reject out-of-pool indices and double-frees so a bad id can never
// re-enter the free list and alias a live slot
if (slot < static_cast<int>(_frameBufferCount) || slot >= static_cast<int>(_srvHeapSize)) {
Framework::Logging::GetLogger(FRAMEWORK_INNER_GRAPHICS)->error("D3D12Backend::FreeSRVSlot, slot {} out of pool range", slot);
return;
}
if (!_srvSlotInUse[slot]) {
Framework::Logging::GetLogger(FRAMEWORK_INNER_GRAPHICS)->error("D3D12Backend::FreeSRVSlot, slot {} not allocated", slot);
return;
}
_srvSlotInUse[slot] = false;
_freeSrvSlots.push_back(static_cast<UINT>(slot));
}

D3D12_CPU_DESCRIPTOR_HANDLE D3D12Backend::GetSRVSlotCPUHandle(int slot) const {
if (!_srvHeap || slot < 0 || slot >= static_cast<int>(_srvHeapSize)) {
return {};
}
auto handle = _srvHeap->GetCPUDescriptorHandleForHeapStart();
handle.ptr += static_cast<SIZE_T>(slot) * _srvDescriptorSize;
return handle;
}

D3D12_GPU_DESCRIPTOR_HANDLE D3D12Backend::GetSRVSlotGPUHandle(int slot) const {
if (!_srvHeap || slot < 0 || slot >= static_cast<int>(_srvHeapSize)) {
return {};
}
auto handle = _srvHeap->GetGPUDescriptorHandleForHeapStart();
handle.ptr += static_cast<UINT64>(slot) * _srvDescriptorSize;
return handle;
}

size_t D3D12Backend::GetFreeSRVSlotCount() const {
std::lock_guard<std::mutex> lock(_srvMutex);
return _freeSrvSlots.size();
}
} // namespace Framework::Graphics
29 changes: 29 additions & 0 deletions code/framework/src/graphics/backend/d3d12.h
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Original file line number Diff line number Diff line change
Expand Up @@ -11,10 +11,16 @@
#include "backend.h"

#include <memory>
#include <mutex>
#include <vector>

namespace Framework::Graphics {
class D3D12Backend: public Backend<ID3D12Device *, ID3D12DeviceContext *, IDXGISwapChain3 *, ID3D12CommandQueue *> {
public:
// Shader-visible SRV slots reserved past the ImGui font descriptors,
// handed to web views via AllocateSRVSlot.
static constexpr UINT kExtraSrvSlots = 64;

private:
IDXGISwapChain3 *_swapChain = nullptr;
UINT _frameBufferCount = 0;
Expand All @@ -23,6 +29,12 @@ namespace Framework::Graphics {
ID3D12GraphicsCommandList *_commandList = nullptr;
ID3D12CommandQueue *_commandQueue = nullptr;

UINT _srvDescriptorSize = 0;
UINT _srvHeapSize = 0;
std::vector<UINT> _freeSrvSlots;
std::vector<bool> _srvSlotInUse;
mutable std::mutex _srvMutex;

struct FrameContext {
ID3D12CommandAllocator *_commandAllocator = nullptr;
ID3D12Resource *_mainRenderTargetResource = nullptr;
Expand All @@ -40,6 +52,23 @@ namespace Framework::Graphics {
void End();
int NumFramesInFlight() const;

// Bounded, shader-visible SRV slot pool shared with ImGui's heap (so handles
// double as ImTextureID). AllocateSRVSlot returns -1 when exhausted; the
// getters return a null handle for any out-of-range slot.
int AllocateSRVSlot();

// Frees an SRV slot from a given slot handle
void FreeSRVSlot(int slot);

// Retrieves a CPU Descriptor handle from a given @p slot handle
D3D12_CPU_DESCRIPTOR_HANDLE GetSRVSlotCPUHandle(int slot) const;

// Retrieves a GPU Descriptor handle from a given @p slot handle
D3D12_GPU_DESCRIPTOR_HANDLE GetSRVSlotGPUHandle(int slot) const;

// Returns number of free SRV slots
size_t GetFreeSRVSlotCount() const;

// TODO: Backend not implemented yet
void BeginDrawing() {}
void EndDrawing() {}
Expand Down