Directx11教程(49) stencil的应用-镜面反射
Directx11教程(49) stencil的应用-镜面反射<div class="postbody"><div id="cnblogs_post_body"> 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.BlendEnable = TRUE;
//blendStateDescription.RenderTarget.SrcBlend = D3D11_BLEND_ONE;
blendStateDescription.RenderTarget.SrcBlend = D3D11_BLEND_BLEND_FACTOR;
blendStateDescription.RenderTarget.DestBlend = D3D11_BLEND_INV_BLEND_FACTOR;
blendStateDescription.RenderTarget.BlendOp = D3D11_BLEND_OP_ADD;
blendStateDescription.RenderTarget.SrcBlendAlpha = D3D11_BLEND_ONE;
blendStateDescription.RenderTarget.DestBlendAlpha = D3D11_BLEND_ZERO;
blendStateDescription.RenderTarget.BlendOpAlpha = D3D11_BLEND_OP_ADD;
blendStateDescription.RenderTarget.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：
http://images.cnblogs.com/cnblogs_com/mikewolf2002/201205/201205152012167817.png
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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