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。





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