dx9和dx11映射的差异

Question

我试图以同样的方式为DX9和DX11生成mipmap，我需要它们从像素着色器中采样特定的级别。在那之后，我注意到在不同的DX版本上，抽样是不同的，而且在DX11中更糟，对DX9更好。

接下来，我尝试通过使用ImGui呈现一个备份副本图像并缩小4倍的大小来可视化它，结果如下：

带有mipmap生成的DX9：dx9 w mips

没有mipmap生成的DX9：dx9

带有mipmap生成的DX11：dx11 w mips

没有mipmap生成的DX11：dx11

纹理的创建是完全相同的：

DX9

static IDirect3DTexture9* pBackBufferResource = nullptr;

IDirect3DSurface9* pBackBuffer = nullptr;
g_pd3dDevice->GetBackBuffer(0U, 0U, D3DBACKBUFFER_TYPE_MONO, &pBackBuffer);

D3DSURFACE_DESC descBack = { };
pBackBuffer->GetDesc(&descBack);

if (pBackBufferResource == nullptr)
{
    g_pd3dDevice->CreateTexture(descBack.Width, descBack.Height, 1U, D3DUSAGE_RENDERTARGET | D3DUSAGE_AUTOGENMIPMAP, descBack.Format, D3DPOOL_DEFAULT, &pBackBufferResource, nullptr);

    /*
     * explicitly set linear filter for mipmap generation
     * for some reason 'D3DSAMP_MIPFILTER' sampler state doesn't actually change this
     */
    pBackBufferResource->SetAutoGenFilterType(D3DTEXF_LINEAR);
}

// get the most detailed mip-level surface
IDirect3DSurface9* pResourceTopSurface = nullptr;
pBackBufferResource->GetSurfaceLevel(0U, &pResourceTopSurface);

// because backbuffer haven't mipmap, we couldn't just copy its texture, we're update only most detailed mip-level
g_pd3dDevice->StretchRect(pBackBuffer, nullptr, pResourceTopSurface, nullptr, D3DTEXF_LINEAR);

// the 'D3DUSAGE_AUTOGENMIPMAP' flag of texture creation will regenerate mipmap automatically, but here do it manually just for sure
pBackBufferResource->GenerateMipSubLevels();

ImVec2 vecMin = { 10.f, 10.f };
ImVec2 vecMax = { vecMin.x + floorf((float)descBack.Width / 4.0f), vecMin.y + floorf((float)descBack.Height / 4.0f) };
ImGui::GetForegroundDrawList()->AddImage(pBackBufferResource, vecMin, vecMax);
ImGui::GetForegroundDrawList()->AddRect(vecMin, vecMax, IM_COL32(0, 0, 0, 255));

DX11

static ID3D11Texture2D* pBackBufferCopy = nullptr;
static ID3D11ShaderResourceView* pBackBufferResource = nullptr;

ID3D11Texture2D* pBackBuffer = nullptr;
g_mainRenderTargetView->GetResource(reinterpret_cast<ID3D11Resource**>(&pBackBuffer));

D3D11_TEXTURE2D_DESC descBack = { };
pBackBuffer->GetDesc(&descBack);

if (pBackBufferCopy == nullptr)
{
    D3D11_TEXTURE2D_DESC descBackCopy = descBack;
    descBackCopy.BindFlags = D3D11_BIND_SHADER_RESOURCE | D3D11_BIND_RENDER_TARGET;
    descBackCopy.MipLevels = 0U;
    descBackCopy.MiscFlags = D3D11_RESOURCE_MISC_GENERATE_MIPS;
    g_pd3dDevice->CreateTexture2D(&descBackCopy, nullptr, &pBackBufferCopy);
}

// because backbuffer haven't mipmap, we couldn't copy its texture just with 'CopyResource()', so we're update only most detailed mip-level
g_pd3dDeviceContext->CopySubresourceRegion(pBackBufferCopy, 0U, 0U, 0U, 0U, pBackBuffer, 0U, nullptr);

pBackBuffer->Release();

if (pBackBufferResource == nullptr)
{
    D3D11_SHADER_RESOURCE_VIEW_DESC resourceViewDescBuffer = { };
    resourceViewDescBuffer.Format = descBack.Format;
    resourceViewDescBuffer.ViewDimension = D3D11_SRV_DIMENSION_TEXTURE2D;
    resourceViewDescBuffer.Texture2D.MostDetailedMip = 0U;
    resourceViewDescBuffer.Texture2D.MipLevels = ~0U;
    g_pd3dDevice->CreateShaderResourceView(pBackBufferCopy, &resourceViewDescBuffer, &pBackBufferResource);
}

// regenerate mipmap based on updated most detailed mip-level
g_pd3dDeviceContext->GenerateMips(pBackBufferResource);

ImVec2 vecMin = { 10.f, 10.f };
ImVec2 vecMax = { vecMin.x + floorf((float)descBack.Width / 4.0f), vecMin.y + floorf((float)descBack.Height / 4.0f) };
ImGui::GetForegroundDrawList()->AddImage(pBackBufferResource, vecMin, vecMax);
ImGui::GetForegroundDrawList()->AddRect(vecMin, vecMax, IM_COL32(0, 0, 0, 255));

MIN/MAG/MIP滤波器的采样状态为线性，MaxLOD为D3D11_FLOAT32_MAX。很明显，DX11图像过于锐利，看上去与w/o映射相同。所以我的问题是为什么它发生在DX11，而不是发生在DX9，当我确信它确实正确地生成mipmap，并且我可以从它们在着色器内采样(着色取样也看起来更清晰)？

Answer 1

一般的答案是自动生成的mipmips完全由驱动程序决定。因此，自动生成的mips的质量因驱动程序的不同而有很大差异，在某些情况下，对于某些格式，它可以像点采样一样低质量。

这实际上是DirectX 12没有“自动生成的mips”功能的原因之一。相反，如果您需要此功能，建议使用计算机着色器。有关示例，请参见用于DirectX的DX12工具包。

尽管如此，您需要验证所有返回HRESULT值的函数，因为您可能会在忽略的某个地方得到一个错误代码。例如，我怀疑在交换链缓冲区上调用SetAutoGenFilterType是否真的像您认为的那样。即使您只是将它们视为快速失败，也不要忽略HRESULT返回。

对于DirectX 11，应该启用调试设备并查找输出。由于DirectX 9是遗留的，因此自Windows7以来就不支持用于它的“调试设备”。