D3D11如何将纹理中alpha值为0的像素渲染为透明？

问题描述

• 我使用了DrawIconEx（GDI / D3D11互操作性和CopyResource）来生成ID3D11Texture2D，该像素具有许多alpha通道值为0的像素。D3D11_USAGE_STAGING/ Map已验证了此纹理，可以查看像素值和{ 3}}保存png（需要修改相关代码：DXGI_FORMAT_B8G8R8A8_UNORM->使用GUID_WICPixelFormat32bppBGRA而不是GUID_WICPixelFormat24bppBGR）。

• 当我使用ScreenGrab的渲染纹理方法时，0像素的alpha值将被渲染为黑色，这不是我想要的，我希望这些像素能够透明。将如何实现目标？这是我的相关代码：

   HRESULT CGraphRender::Init()
   {
       ...
  
       // Create an alpha enabled blend state description.
       _blend_state = nullptr;
  
       D3D11_BLEND_DESC blendDesc;
       ZeroMemory(&blendDesc,sizeof(D3D11_BLEND_DESC));
  
       blendDesc.RenderTarget[0].BlendEnable = TRUE;   
       blendDesc.RenderTarget[0].SrcBlend = D3D11_BLEND_SRC_ALPHA;
       blendDesc.RenderTarget[0].DestBlend = D3D11_BLEND_INV_SRC_ALPHA;
       blendDesc.RenderTarget[0].BlendOp = D3D11_BLEND_OP_ADD;
       blendDesc.RenderTarget[0].SrcBlendAlpha = D3D11_BLEND_ONE;
       blendDesc.RenderTarget[0].DestBlendAlpha = D3D11_BLEND_ZERO;
       blendDesc.RenderTarget[0].BlendOpAlpha = D3D11_BLEND_OP_ADD;
       blendDesc.RenderTarget[0].RenderTargetWriteMask = D3D11_COLOR_WRITE_ENABLE_ALL;
  
       hr = _d3d_device->CreateBlendState(&blendDesc,&_blend_state);
       RETURN_ON_FAIL(hr);
  
       ....
   }
  
   HRESULT CGraphRender::Clear_3D(float color[])
   {
       ID3D11RenderTargetView* rtv[] = { _back_rendertarget_view };
       _immediate_context->OMSetRenderTargets(_countof(rtv),rtv,nullptr);
       _immediate_context->ClearRenderTargetView(_back_rendertarget_view,color);
  
       float blendFactor[4] = { 1.f,1.f,1.f };
       _immediate_context->OMSetBlendState(_blend_state,blendFactor,0xffffffff);
  
       return S_OK;
   }
  

解决方法

问题已解决：在渲染“ alpha”纹理之前执行OMGetBlendState（_blend_state ...设置，并在渲染后恢复默认的blendstate

HRESULT CGraphRender::DrawTexture(const std::shared_ptr<CDrawTextureShader>& texture,const RECT& dst_rect,const BOOL& is_blend_alpha)
{
    CComPtr<ID3D11DeviceContext> immediate_context;
    _d3d_device->GetImmediateContext(&immediate_context);
    if (!immediate_context)
    {
        return E_UNEXPECTED;
    }

    if (is_blend_alpha)
    {
        CComPtr<ID3D11BlendState> old_blend_state;
        FLOAT   old_blend_factor[4] = { 0.f };
        UINT    old_sample_mask = 0;

        immediate_context->OMGetBlendState(&old_blend_state,old_blend_factor,&old_sample_mask);

        float blend_factor[4] = { 1.f,1.f,1.f };
        immediate_context->OMSetBlendState(_blend_state,blend_factor,0xffffffff);

        HRESULT hr = texture->Render(immediate_context,dst_rect);

        immediate_context->OMSetBlendState(old_blend_state,old_sample_mask);

        return hr;
    }
    else
    {
        return texture->Render(immediate_context,dst_rect);
    }
}