feat: 实现 D3D12DescriptorHeap 描述符堆类

- 添加 D3D12DescriptorHeap.h 头文件
- 实现 ID3D12DescriptorHeap 封装
- 支持 RTV、DSV、CBV_SRV_UAV、Sampler 堆类型
- 支持 GPU 可见描述符堆
- 添加 GetCPUDescriptorHandle、GetGPUDescriptorHandle 等方法
- 测试通过

engine/src/RHI/D3D12DescriptorHeap.cpp

@@ -0,0 +1,62 @@
+#include "XCEngine/RHI/D3D12/D3D12DescriptorHeap.h"
+
+namespace XCEngine {
+namespace RHI {
+
+D3D12DescriptorHeap::D3D12DescriptorHeap()
+    : m_type(DescriptorHeapType::CBV_SRV_UAV)
+    , m_numDescriptors(0)
+    , m_descriptorSize(0)
+    , m_shaderVisible(false) {
+}
+
+D3D12DescriptorHeap::~D3D12DescriptorHeap() {
+    Shutdown();
+}
+
+bool D3D12DescriptorHeap::Initialize(ID3D12Device* device, DescriptorHeapType type, uint32_t numDescriptors, bool shaderVisible) {
+    D3D12_DESCRIPTOR_HEAP_DESC desc = {};
+    desc.Type = ToD3D12(type);
+    desc.NumDescriptors = numDescriptors;
+    desc.Flags = shaderVisible ? D3D12_DESCRIPTOR_HEAP_FLAG_SHADER_VISIBLE : D3D12_DESCRIPTOR_HEAP_FLAG_NONE;
+    desc.NodeMask = 0;
+
+    HRESULT hResult = device->CreateDescriptorHeap(&desc, IID_PPV_ARGS(&m_descriptorHeap));
+    if (FAILED(hResult)) {
+        return false;
+    }
+
+    m_type = type;
+    m_numDescriptors = numDescriptors;
+    m_shaderVisible = shaderVisible;
+    m_descriptorSize = device->GetDescriptorHandleIncrementSize(ToD3D12(type));
+
+    return true;
+}
+
+void D3D12DescriptorHeap::Shutdown() {
+    m_descriptorHeap.Reset();
+}
+
+D3D12_CPU_DESCRIPTOR_HANDLE D3D12DescriptorHeap::GetCPUDescriptorHandle(uint32_t index) const {
+    D3D12_CPU_DESCRIPTOR_HANDLE handle = m_descriptorHeap->GetCPUDescriptorHandleForHeapStart();
+    handle.ptr += index * m_descriptorSize;
+    return handle;
+}
+
+D3D12_GPU_DESCRIPTOR_HANDLE D3D12DescriptorHeap::GetGPUDescriptorHandle(uint32_t index) const {
+    D3D12_GPU_DESCRIPTOR_HANDLE handle = m_descriptorHeap->GetGPUDescriptorHandleForHeapStart();
+    handle.ptr += index * m_descriptorSize;
+    return handle;
+}
+
+D3D12_CPU_DESCRIPTOR_HANDLE D3D12DescriptorHeap::GetCPUDescriptorHandleForHeapStart() const {
+    return m_descriptorHeap->GetCPUDescriptorHandleForHeapStart();
+}
+
+D3D12_GPU_DESCRIPTOR_HANDLE D3D12DescriptorHeap::GetGPUDescriptorHandleForHeapStart() const {
+    return m_descriptorHeap->GetGPUDescriptorHandleForHeapStart();
+}
+
+} // namespace RHI
+} // namespace XCEngine