z-fighting在unity中的解決方式

如果在畫面中，發現有畫面閃爍的問題。那么大多數情況下是z-fighting引起的，

解決方案：

1, 在每個場景中，找到那個MainCamera，然后在Inspector上，找到MainCamera的屬性，Clipping Planes，需要做的是盡量放大near的值，盡量減小far的值。根據我的實驗結果，同樣改動Near值的幅度比Far值的幅度相對來說效果會更好。如Near從1到20可能修正了某個z-fighting，但是Far從1000改到500也還是沒有用。這個在實踐中可以注意。

 

2, 如果場景沒有辦法改動上述的值，那么還有的方式就是找到產生z-fighting的模型，讓模型產生這個現象的兩個面盡量離開一些距離，究竟多少距離只有通過實驗才知道。

 

3, 如果可能，程序上就可以用Polygon Offset，這個是OpenGL的接口，

 

 

drawOnePlane();

//Draw other plane in the almost same position, before use offset, it will fighting with the one we has drawn.
glEnable( GL_POLYGON_OFFSET_FILL );
glPolygonOffset( g_OffsetFactor, g_OffsetUnit );

drawOtherPlane();

glPolygonOffset( 0.0f, 0.0f );
glDisable( GL_POLYGON_OFFSET_FILL );

 

4、如果是D3D，那么這篇文章提到3中方式，最后一種方式是跟上面的OpenGL思路一樣的。

 

http://software.intel.com/zh-cn/articles/alternatives-to-using-z-bias-to-fix-z-fighting-issues/

 

a, project matrix

 

 

// ZFighting Solution #1 - Projection Matrix
D3DXMATRIX mProjectionMat;   // Holds default projection matrix
D3DXMATRIX mZBiasedProjectionMat;   // Holds ZBiased projection matrix
// Globals used for Projection matrix
float g_fBaseNearClip   =   1.0f;
float g_fBaseFarClip    = 100.0f;
// Code indicates no change. ie states 'near and far clipping planes pushed out' but only far appears pushed
float g_fNearClipBias   =   0.0f;
float g_fFarClipBias    =   0.5f;

// Projection Matrix work around
// Best if calculation are done outside of render function.

// The "zbiased" projection has it near and far clipping
// planes pushed out...
D3DXMatrixPerspectiveFovLH( &mZBiasedProjectionMat, D3DX_PI/4,(mProjectionMat._22/mProjectionMat._11),
g_fBaseNearClip + g_fNearClipBias,
g_fBaseFarClip + g_fFarClipBias  );
. . .

// Original projection is loaded
m_pd3dDevice ->SetTransform( D3DTS_PROJECTION, & mProjectionMat);

// Billboards are rendered...

// The "zbiased" projection is loaded ...
m_pd3dDevice->SetTransform(D3DTS_PROJECTION, &mZBiasedProjectionMat);

// Posters are rendered...

// Original projection is reloaded...
g_pd3dDevice->SetTransform( D3DTS_PROJECTION, & mProjectionMat);

. . .

 

 

b, view port matrix

 

// ZFighting Solution #2 - Viewport
D3DVIEWPORT9 mViewport;             // Holds viewport data
D3DVIEWPORT9 mNewViewport;          // Holds new viewport data

// Global used for Viewport
// Hard coded for ZBIAS of 1 using this formula
//          MinZ - 256/(2^24-1) and
//          MaxZ - 256/(2^24-1)
// 2^24 comes from the amount of Zbits and the 256 works
// for Intel (R) Integrated Graphics, but can be any
// multiple of 16.
float g_fViewportBias   = 0.0000152588f;

// Projection Matrix work around
// Viewport work around
m_pd3dDevice->GetViewport(&mViewport);

// Copy old Viewport to new
mNewViewport = mViewport;

// Change by the bias
mNewViewport.MinZ -= g_fViewportBias;
mNewViewport.MaxZ -= g_fViewportBias;
. . .

// Original viewport is reloaded …
m_pd3dDevice->SetViewport(&mViewport);

// Billboards are rendered …

// The new viewport is loaded …
m_pd3dDevice->SetViewport(&mNewViewport);

// Posters are rendered …

// Original viewport is reloaded …
m_pd3dDevice->SetViewport(&mViewport);

. . .

 

c, depth - bias

 

BOOL                    m_bDepthBiasCap;        // TRUE, if device has DepthBias Caps

// Globals used for Depth Bias
float g_fSlopeScaleDepthBias    = 1.0f;
float g_fDepthBias              = -0.0005f;
float g_fDefaultDepthBias       = 0.0f;

// Check for devices which support the new depth bias caps
if ((pCaps->RasterCaps & D3DPRASTERCAPS_SLOPESCALEDEPTHBIAS) &&
     (pCaps->RasterCaps & D3DPRASTERCAPS_DEPTHBIAS))
{
    m_bDepthBiasCap = true;        // TRUE, if DepthBias Caps
}

// Billboards are rendered...

// DepthBias work around
if ( m_bDepthBiasCap ) // TRUE, if DepthBias supported
{
    // Used to determine how much bias can be applied
    // to co-planar primitives to reduce z fighting
    // bias = (max * D3DRS_SLOPESCALEDEPTHBIAS) + D3DRS_DEPTHBIAS,
    // where max is the maximum depth slope of the triangle being rendered.
    m_pd3dDevice->SetRenderState(D3DRS_SLOPESCALEDEPTHBIAS, F2DW(g_fSlopeScaleDepthBias));
    m_pd3dDevice->SetRenderState(D3DRS_DEPTHBIAS, F2DW(g_fDepthBias));
}

// Posters are rendered...

if ( m_bDepthBiasCap ) // TRUE, if DepthBias supported
{
    // DepthBias work around
    // set it back to zero (default)
    m_pd3dDevice->SetRenderState(D3DRS_SLOPESCALEDEPTHBIAS, F2DW(g_fDefaultDepthBias));
    m_pd3dDevice->SetRenderState(D3DRS_DEPTHBIAS, F2DW(g_fDefaultDepthBias));
}

. . .

 

5，這里還有一篇文章教到怎么樣在面上畫出線的，相信你也會遇到同樣的問題。當然，核心還是用depth-bias，但是，人家把怎么做和做的時候要注意的問題都寫上了（主要就是用bias的時候值不要取的太大，否則線框是渲染出來了，但是也同時多出線來了，因為本來是該本剪切的，經過修正可能就不被剪切了）。值得一看。

 

http://www.catalinzima.com/samples/12-months-12-samples-2008/drawing-wireframes-without-z-fighting/

 

背景原理：

z-fighting的出現是的不同面上的像素在z-buffer中的值相近，導致前台取像素的時候一會去這個面的，一會取那個面的。改變照相機的near、far屬性會涉及到z-buffer中的值的精度。因為在各個平台上z-buffer位數不同，因此改變near和far能給z-buffer中的值的浮點數部分盡量留出空間，消除z-fighting。

 

這個是wiki上的z-fighting的例子，可以看到不同色彩的面，因為z-buffer的精度設置的小，然后兩個面放置的比較近，因此出現了相關的穿插顯示的問題。