d3d12 渲染超大图片代码

在 D3D12 中，渲染超大图片可以使用纹理切割技术，将大型纹理分成多个小型纹理，并将它们分别加载到显存中。然后，在渲染时，可以使用纹理数组来绘制超过功能级别最大纹理大小的图片。

下面是使用纹理切割渲染超大图片的代码示例：

// 定义纹理大小
const UINT textureWidth = 4096;
const UINT textureHeight = 4096;

// 加载大型纹理
ComPtr<ID3D12Resource> textureResource;
ThrowIfFailed(CreateTextureFromFile(device, commandList, L"large_texture.png", textureResource.GetAddressOf()));

// 创建小型纹理
const UINT subTextureWidth = 512;
const UINT subTextureHeight = 512;

for (UINT y = 0; y < textureHeight; y += subTextureHeight)
{
    for (UINT x = 0; x < textureWidth; x += subTextureWidth)
    {
        // 计算子纹理的大小和位置
        const UINT subTextureX = x;
        const UINT subTextureY = y;
        const UINT subTextureW = min(subTextureWidth, textureWidth - x);
        const UINT subTextureH = min(subTextureHeight, textureHeight - y);

        // 创建子纹理资源
        ComPtr<ID3D12Resource> subTextureResource;
        ThrowIfFailed(device->CreateCommittedResource(..., D3D12_RESOURCE_STATE_COPY_DEST, ...));

        // 将大型纹理的子区域复制到小型纹理中
        D3D12_TEXTURE_COPY_LOCATION srcLocation = CD3DX12_TEXTURE_COPY_LOCATION(textureResource.Get(), subTextureX, subTextureY, 0);
        D3D12_TEXTURE_COPY_LOCATION dstLocation = CD3DX12_TEXTURE_COPY_LOCATION(subTextureResource.Get(), 0, 0, 0);
        commandList->CopyTextureRegion(&dstLocation, 0, 0, 0, &srcLocation, nullptr);

        // 添加小型纹理到纹理数组中
        m_textureArray.push_back(subTextureResource);
    }
}

// 绑定纹理数组到着色器资源视图
CD3DX12_CPU_DESCRIPTOR_HANDLE srvHandle(m_srvDescriptorHeap->GetCPUDescriptorHandleForHeapStart());
for (UINT i = 0; i < m_textureArray.size(); i++)
{
    device->CreateShaderResourceView(m_textureArray[i].Get(), nullptr, srvHandle);
    srvHandle.Offset(m_srvDescriptorSize);
}

// 绘制超大图片
const UINT numVertices = 4;
const UINT vertexBufferSize = sizeof(Vertex) * numVertices;

Vertex quadVertices[] =
{
    { { -1.0f,  1.0f, 0.0f }, { 0.0f, 0.0f } },
    { {  1.0f,  1.0f, 0.0f }, { 1.0f, 0.0f } },
    { { -1.0f, -1.0f, 0.0f }, { 0.0f, 1.0f } },
    { {  1.0f, -1.0f, 0.0f }, { 1.0f, 1.0f } }
};

ComPtr<ID3D12Resource> vertexBuffer;
ThrowIfFailed(device->CreateCommittedResource(..., D3D12_RESOURCE_STATE_COPY_DEST, ...));

ComPtr<ID3D12Resource> vertexUploadBuffer;
ThrowIfFailed(device->CreateCommittedResource(..., D3D12_RESOURCE_STATE_GENERIC_READ, ...));

D3D12_SUBRESOURCE_DATA vertexData = {};
vertexData.pData = reinterpret_cast<BYTE*>(quadVertices);
vertexData.RowPitch = vertexBufferSize;
vertexData.SlicePitch = vertexBufferSize;

UpdateSubresources(commandList, vertexBuffer.Get(), vertexUploadBuffer.Get(), 0, 0, 1, &vertexData);
commandList->ResourceBarrier(..., D3D12_RESOURCE_STATE_VERTEX_AND_CONSTANT_BUFFER, ...);

commandList->IASetVertexBuffers(...);

commandList->IASetPrimitiveTopology(D3D_PRIMITIVE_TOPOLOGY_TRIANGLESTRIP);

CD3DX12_GPU_DESCRIPTOR_HANDLE srvGpuHandle(m_srvDescriptorHeap->GetGPUDescriptorHandleForHeapStart());
commandList->SetGraphicsRootDescriptorTable(0, srvGpuHandle);

commandList->DrawInstanced(numVertices, 1, 0, 0);

// 清理资源
m_textureArray.clear();

在这个示例中，我们首先加载大型纹理，然后将其分成多个小型纹理。然后，我们将每个小型纹理复制到单独的资源中，并将它们添加到纹理数组中。最终，我们绑定纹理数组到着色器资源视图中，并使用它来绘制超过功能级别最大纹理大小的图片。

需要注意的是，纹理切割技术会增加额外的资源开销和绘制开销，因此应该尽可能地避免使用超过功能级别最大纹理大小的图片。