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Depth Bias收藏

An application can help ensure that coplanar polygons are rendered properly by adding a bias to the z-values that the system uses when rendering the sets of coplanar polygons. To add a z-bias to a set of polygons, call the SetRenderState method just before rendering them, setting the State parameter to D3DRS_DEPTHBIAS, and the value parameter to a value between 0-16 inclusive. A higher z-bias value increases the likelihood that the polygons you render will be visible when displayed with other coplanar polygons.


Offset = m * D3DRS_SLOPESCALEDEPTHBIAS + D3DRS_DEPTHBIAS

where m is the maximum depth slope of the triangle being rendered.

m = max(abs(delta z / delta x), abs(delta z / delta y))

The units for the D3DRS_DEPTHBIAS and D3DRS_SLOPESCALEDEPTHBIAS render states depend on whether z-buffering or w-buffering is enabled. The application must provide suitable values.

The bias is not applied to any line and point primitive. However, this bias needs to be applied to triangles drawn in wireframe mode.

// RenderStates
D3DRS_SLOPESCALEDEPTHBIAS, // Defaults to zero
D3DRS_DEPTHBIAS, // Defaults to zero

// Caps
D3DPRASTERCAPS_DEPTHBIAS
D3DPRASTERCAPS_SLOPESCALEDEPTHBIAS

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另外一篇 英文资料（转自 http://www.intel.com/cd/ids/developer/apac/zho/dc/games/optimization/170939.htm?page=4）
使用Z-Bias解决Z-Fighting问题的替代方案
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目录
Introduction
Alternative Method 1: Projection Matrix
Alternative Method 2: Viewport
Alternative Method 3: Depth Bias
Conclusion
Additional Resources

Alternative Method 3: Depth Bias

The last method addressed in this article uses the DirectX 9 Depth Bias method to solve z-fighting. A check to verify that the graphics card is capable of performing depth bias is needed. Intel Integrated Graphics will support depth bias in the next graphics core code named Grantsdale. After checking the cap bits to verify that depth bias is supported, this technique merely requires setting D3DRS_SLOPESCALEDEPTHBIAS and D3DRS_DEPTHBIAS to the proper values to get the desired effect.

The following code snippet shows the depth-bias alternative to using a DirectX z-bias call:

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));
}

. . .

Like the other methods (and like the original z-bias), some tweaking may be necessary, but using D3DRS_SLOPESCALEDEPTHBIAS and D3DRS_DEPTHBIAS is a relatively consistent technique for resolving z-fighting issues across a wide selection of graphics devices. The figure below shows the result of this alternate solution:


Figure 4. Z-fighting solved with depth bias solution.
As Figure 4 shows, care should be taken for adjusting the D3DRS_SLOPESCALEDEPTHBIAS and D3DRS_DEPTHBIAS. They can be very sensitive and lead to other issues like the problem below for distant objects:


Figure 5. Depth-bias solution possible issue: unwanted overlapping polygons.  回复  更多评论
  

dw/D = (far_clip - near_clip)/near_clip;
这个公式怎么得出来的？  回复  更多评论
  

(x,y,z,1) *
xScale 0 0 0
0 yScale 0 0
0 0 zf/(zf-zn) 1
0 0 -zn*zf/(zf-zn) 0
之后，z变为了z'
z' = zf*(z - zn)/(zf-zn)
怎么会是dw/D = (far_clip - near_clip)/near_clip?  回复  更多评论
  

good  回复  更多评论
  

这个东西好像没法用哦  回复  更多评论
  

懒东西，最近怎么不跟新博客了？  回复  更多评论