z-fighting在unity中的解决方式

如果在画面中，发现有画面闪烁的问题。那么大多数情况下是z-fighting引起的，

解决方案：

1, 在每个场景中，找到那个MainCamera，然后在Inspector上，找到MainCamera的属性，Clipping Planes，需要做的是尽量放大near的值，尽量减小far的值。根据我的实验结果，同样改动Near值的幅度比Far值的幅度相对来说效果会更好。如Near从1到20可能修正了某个z-fighting，但是Far从1000改到500也还是没有用。这个在实践中可以注意。

 

2, 如果场景没有办法改动上述的值，那么还有的方式就是找到产生z-fighting的模型，让模型产生这个现象的两个面尽量离开一些距离，究竟多少距离只有通过实验才知道。

 

3, 如果可能，程序上就可以用Polygon Offset，这个是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，那么这篇文章提到3中方式，最后一种方式是跟上面的OpenGL思路一样的。

 

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，这里还有一篇文章教到怎么样在面上画出线的，相信你也会遇到同样的问题。当然，核心还是用depth-bias，但是，人家把怎么做和做的时候要注意的问题都写上了（主要就是用bias的时候值不要取的太大，否则线框是渲染出来了，但是也同时多出线来了，因为本来是该本剪切的，经过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的出现是的不同面上的像素在z-buffer中的值相近，导致前台取像素的时候一会去这个面的，一会取那个面的。改变照相机的near、far属性会涉及到z-buffer中的值的精度。因为在各个平台上z-buffer位数不同，因此改变near和far能给z-buffer中的值的浮点数部分尽量留出空间，消除z-fighting。

 

这个是wiki上的z-fighting的例子，可以看到不同色彩的面，因为z-buffer的精度设置的小，然后两个面放置的比较近，因此出现了相关的穿插显示的问题。