Directx11教程(49) stencil的应用-镜面反射

     本教程中,我们利用stencil来实现一个镜面反射效果。

1、首先我们要在D3DClass中增加几个成员变量及函数。

ID3D11DepthStencilState* m_depthStencilStateMirror;
ID3D11DepthStencilState* m_depthStencilStateReflect;

m_depthStencilStateMirror是渲染镜子时候,使用的depth stencil 状态,我们设置stencil 函数为D3D11_COMPARISON_ALWAYS,这样,stencil测试总能pass,然后pass的操作为D3D11_STENCIL_OP_REPLACE,这样,会用设置的ref值填充stencil buffer。

depthStencilDesc.DepthEnable = true;
depthStencilDesc.DepthWriteMask = D3D11_DEPTH_WRITE_MASK_ALL

depthStencilDesc.DepthFunc = D3D11_COMPARISON_LESS;

depthStencilDesc.StencilEnable = true;
depthStencilDesc.StencilReadMask = 0xFF;
depthStencilDesc.StencilWriteMask = 0xFF;

// 对于front face 像素使用的模版操作操作.
depthStencilDesc.FrontFace.StencilFailOp = D3D11_STENCIL_OP_KEEP;
depthStencilDesc.FrontFace.StencilDepthFailOp = D3D11_STENCIL_OP_KEEP;
depthStencilDesc.FrontFace.StencilPassOp = D3D11_STENCIL_OP_REPLACE;
depthStencilDesc.FrontFace.StencilFunc = D3D11_COMPARISON_ALWAYS;

// 对于back face像素使用的模版操作模式.
depthStencilDesc.BackFace.StencilFailOp = D3D11_STENCIL_OP_KEEP;
depthStencilDesc.BackFace.StencilDepthFailOp = D3D11_STENCIL_OP_DECR;
depthStencilDesc.BackFace.StencilPassOp = D3D11_STENCIL_OP_REPLACE;
depthStencilDesc.BackFace.StencilFunc = D3D11_COMPARISON_ALWAYS;

// 创建深度模版状态,使其生效
result = m_device->CreateDepthStencilState(&depthStencilDesc, &m_depthStencilStateMirror);
if(FAILED(result))
    {
    HR(result);
    return false;

    }

m_depthStencilStateReflect用来渲染镜子中反射的物体,此时禁止depth test,使depth test总是pass,stencil函数用等于比较,及当前的stencil ref值和stencil buffer中的值比较,等于则pass stencil test。

// 设置reflect object深度模版状态描述.
depthStencilDesc.DepthEnable = true;
depthStencilDesc.DepthWriteMask = D3D11_DEPTH_WRITE_MASK_ZERO;//D3D11_DEPTH_WRITE_MASK_ZERO禁止写深度缓冲
depthStencilDesc.DepthFunc = D3D11_COMPARISON_ALWAYS;

// 对于front face 像素使用的模版操作操作.
depthStencilDesc.FrontFace.StencilPassOp = D3D11_STENCIL_OP_KEEP;
depthStencilDesc.FrontFace.StencilFunc = D3D11_COMPARISON_EQUAL;

// 创建深度模版状态,使其生效
result = m_device->CreateDepthStencilState(&depthStencilDesc, &m_depthStencilStateReflect);
if(FAILED(result))
    {
    HR(result);
    return false;

    }

m_alphaEnableBlendingState状态变量创建一个alpha blend状态,这个状态主要在渲染镜子中物体时候使用,因为我们的镜面是一个纹理表示,alpha blend会把镜面纹理和渲染物体进行混合操作。

// 创建一个alpha blend状态.
blendStateDescription.RenderTarget[0].BlendEnable = TRUE;
//blendStateDescription.RenderTarget[0].SrcBlend = D3D11_BLEND_ONE;
blendStateDescription.RenderTarget[0].SrcBlend = D3D11_BLEND_BLEND_FACTOR;
blendStateDescription.RenderTarget[0].DestBlend = D3D11_BLEND_INV_BLEND_FACTOR;
blendStateDescription.RenderTarget[0].BlendOp = D3D11_BLEND_OP_ADD;
blendStateDescription.RenderTarget[0].SrcBlendAlpha = D3D11_BLEND_ONE;
blendStateDescription.RenderTarget[0].DestBlendAlpha = D3D11_BLEND_ZERO;
blendStateDescription.RenderTarget[0].BlendOpAlpha = D3D11_BLEND_OP_ADD;
blendStateDescription.RenderTarget[0].RenderTargetWriteMask = D3D11_COLOR_WRITE_ENABLE_ALL;//0x0f;

// 用描述符创建一个alpha blend状态
result = m_device->CreateBlendState(&blendStateDescription, &m_alphaEnableBlendingState);
if(FAILED(result))
    {
    return false;
    }

另外还有一个函数ChangeBackCullMode(bool b),用来改变渲染状态,设置front face 为顺时针渲染。因为在渲染镜子中物体时候,镜子中物体正面其实对应物体的反面,这是需要改变渲染次序。

下面的几个函数用来改变这几个新增加的状态。

void TurnOnAlphaBlending();
void TurnOffAlphaBlending();
void ChangeBackCullMode(bool b);

void EnableDefaultDepthStencil();
void EnableMirrorDepthStencil();
void EnableReflectDepthStencil();

2、D3Dclass中的BeginSence函数小改动,每帧渲染之前清除stencil值为0

void D3DClass::BeginScene(float red, float green, float blue, float alpha)
    {

    //清除深度缓冲.
    m_deviceContext->ClearDepthStencilView(m_depthStencilView, D3D11_CLEAR_DEPTH|D3D11_CLEAR_STENCIL, 1.0f, 0);


    return;
    }

3、增加了一个MirrorModelClass类用来表示镜子的mesh。

4、在graphicsClass类中依次渲染物体

    首先渲染地面,墙以及box

    m_D3D->EnableMirrorDepthStencil();

    渲染镜子

     m_D3D->EnableDefaultDepthStencil();

     定义镜子反射平面,计算反射矩阵,注意D3DXMatrixReflect计算反射矩阵时候,对平面进行了归一化,所以我加了一个平移操作。

D3DXPLANE mirrorPlane(0.0, 0.0, 10.99, 0.0);
D3DXMATRIX R;
//得到基于mirrorPlane平面的反射矩阵
D3DXMatrixReflect(&R, &mirrorPlane);
//box在原点位置,没有变化,它的世界坐标矩阵为worldMatrix
D3DXMATRIX W = worldMatrix * R;
D3DXMatrixTranslation(&worldMatrix1, 0.0, 0.0, -18.0);
W = worldMatrix1*W;

     接下来,设置状态

m_D3D->EnableReflectDepthStencil();
m_D3D->TurnOnAlphaBlending();
m_D3D->ChangeBackCullMode(true);

渲染镜子中box

m_D3D->EnableDefaultDepthStencil();
m_D3D->TurnOffAlphaBlending();
m_D3D->ChangeBackCullMode(false);

程序最终的效果如下:

Directx11教程(49) stencil的应用-镜面反射_第1张图片

完整的代码请参考:

工程文件myTutorialD3D11_43

代码下载:

http://files.cnblogs.com/mikewolf2002/d3d1139-49.zip

http://files.cnblogs.com/mikewolf2002/pictures.zip

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