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我使用直徑從下面的實施了LoD。在「外殼着色器：鑲嵌LOD」一章中，有一個很好的直徑LoD。這裏良好的報價：DX11鑲嵌直徑不正確鑲嵌值的LOD
對於每個補丁邊緣，着色器計算邊長，然後在概念上符合它周圍的球體。球體投影到屏幕空間，其屏幕空間直徑用於計算邊緣的曲面細分因子。
這裏我HullShader：
// Globals
cbuffer TessellationBuffer // buffer need to be aligned to 16!!
{
float4 cameraPosition;
float tessellatedTriSize;
float3 padding;
matrix worldMatrix;
matrix projectionMatrix;
};
// Typedefs
struct HullInputType
{
float4 position : SV_POSITION;
float2 tex : TEXCOORD0;
float3 normal : NORMAL;
};
struct ConstantOutputType
{
float edges[3] : SV_TessFactor;
float inside : SV_InsideTessFactor;
};
struct HullOutputType
{
float4 position : SV_POSITION;
float2 tex : TEXCOORD0;
float3 normal : NORMAL;
};
// Rounding function
float roundTo2Decimals(float value)
{
value *= 100;
value = round(value);
value *= 0.01;
return value;
}
float calculateLOD(float4 patch_zero_pos, float4 patch_one_pos)//1,3,1,1; 3,3,0,1
{
float diameter = 0.0f;
float4 radiusPos;
float4 patchDirection;
// Calculates the distance between the patches and fits a sphere around.
diameter = distance(patch_zero_pos, patch_one_pos); // 2.23607
float radius = diameter/2; // 1.118035
patchDirection = normalize(patch_one_pos - patch_zero_pos); // 0.894,0,-0.447,0 direction from base edge_zero
// Calculate the position of the radiusPos (center of sphere) in the world.
radiusPos = patch_zero_pos + (patchDirection * radius);//2,3,0.5,1
radiusPos = mul(radiusPos, worldMatrix);
// Get the rectangular points of the sphere to the camera.
float4 camDirection;
// Direction from camera to the sphere center.
camDirection = normalize(radiusPos - cameraPosition); // 0.128,0,0.99,0
// Calculates the orthonormal basis (sUp,sDown) of a vector camDirection.
// Find the smallest component of camDirection and set it to 0. swap the two remaining
// components and negate one of them to find sUp_ which can be used to find sDown.
float4 sUp_;
float4 sUp;
float4 sDown;
float4 sDownAbs;
sDownAbs = abs(camDirection);//0.128, 0 ,0.99, 0
if(sDownAbs.y < sDownAbs.x && sDownAbs.y < sDownAbs.z) { //0.99, 0, 0.128
sUp_.x = -camDirection.z;
sUp_.y = 0.0f;
sUp_.z = camDirection.x;
sUp_.w = camDirection.w;
} else if(sDownAbs.z < sDownAbs.x && sDownAbs.z < sDownAbs.y){
sUp_.x = -camDirection.y;
sUp_.y = camDirection.x;
sUp_.z = 0.0f;
sUp_.w = camDirection.w;
}else{
sUp_.x = 0.0f;
sUp_.y = -camDirection.z;
sUp_.z = camDirection.y;
sUp_.w = camDirection.w;
}
// simple version
// sUp_.x = -camDirection.y;
// sUp_.y = camDirection.x;
// sUp_.z = camDirection.z;
// sUp_.w = camDirection.w;
sUp = sUp_/length(sUp_); // =(0.99, 0, 0.128,0)/0.99824 = 0.991748,0,0.128226,0
sDown = radiusPos - (sUp * radius); // 0.891191,3,0.356639,1 = (2,3,0.5,1) - (0.991748,0,0.128226,0)*1.118035
sUp = radiusPos + (sUp * radius); // = (3.10881,3,0.643361,1)
// Projects sphere in projection space (2d).
float4 projectionUp = mul(sUp, projectionMatrix);
float4 projectionDown = mul(sDown, projectionMatrix);
// Calculate tessellation factor for this edge according to the diameter on the screen.
float2 sUp_2;
sUp_2.x = projectionUp.x;
sUp_2.y = projectionUp.y;
float2 sDown_2;
sDown_2.x = projectionDown.x;
sDown_2.y = projectionDown.y;
// Distance between the 2 points in 2D
float projSphereDiam = distance(sUp_2, sDown_2);
//Debug
//return tessellatedTriSize;
//if(projSphereDiam < 2.0f)
// return 1.0f;
//else if(projSphereDiam < 10.0f)
// return 2.0f;
//else
// return 10.0f;
return projSphereDiam*tessellatedTriSize;
}
// Patch Constant Function
// set/calculate any data constant to entire patch.
// is invoked once per patch
// direction vector w = 0 ; position vector w = 1
// receives as input a patch with 3 control points and each control point is represented by the structure of HullInputType
// patch control point should be displaced vertically, this can significantly affect the distance of the camera
// patchId is an identifier number of the patch generated by the Input Assembler
ConstantOutputType ColorPatchConstantFunction(InputPatch<HullInputType, 3> inputPatch, uint patchId : SV_PrimitiveID)
{
ConstantOutputType output;
////ret distance(x, y) Returns a distance scalar between two vectors.
float ret, retinside;
retinside = 0.0f;
float4 patch_zero_pos;//1,3,1,1
patch_zero_pos = float4(inputPatch[0].position.xyz, 1.0f);
float4 patch_one_pos;//3,3,0,1
patch_one_pos = float4(inputPatch[1].position.xyz, 1.0f);
float4 patch_two_pos;
patch_two_pos = float4(inputPatch[2].position.xyz, 1.0f);
// calculate LOD by diametersize of the edges
ret = calculateLOD(patch_zero_pos, patch_one_pos);
ret = roundTo2Decimals(ret);// rounding
output.edges[0] = ret;
retinside += ret;
ret = calculateLOD(patch_one_pos, patch_two_pos);
ret = roundTo2Decimals(ret);// rounding
output.edges[1] = ret;
retinside += ret;
ret = calculateLOD(patch_two_pos, patch_zero_pos);
ret = roundTo2Decimals(ret);// rounding
output.edges[2] = ret;
retinside += ret;
// Set the tessellation factor for tessallating inside the triangle.
// see image tessellationOuterInner
retinside *= 0.333;
// rounding
retinside = roundTo2Decimals(retinside);
output.inside = retinside;
return output;
}
// Hull Shader
// The hull shader is called for each output control point.
// Trivial pass through
[domain("tri")]
[partitioning("fractional_odd")] //fractional_odd
[outputtopology("triangle_cw")]
[outputcontrolpoints(3)]
[patchconstantfunc("ColorPatchConstantFunction")]
HullOutputType ColorHullShader(InputPatch<HullInputType, 3> patch, uint pointId : SV_OutputControlPointID, uint patchId : SV_PrimitiveID)
{
HullOutputType output;
// Set the position for this control point as the output position.
output.position = patch[pointId].position;
// Set the input color as the output color.
output.tex = patch[pointId].tex;
output.normal = patch[pointId].normal;
return output;
}
一些圖形explenation的代碼： 首先找到兩個頂點之間的中心 
查找正交基（矩形到相機方向）從相機上「圓」 
項目sUp和sDown在Projection空間中計算長度以計算曲面細分因子。 
的問題
鑲嵌工作的罰款。但由於某些測試原因，我讓對象旋轉，所以我可以看到曲面細分是否隨着旋轉而發生。一些我認爲它不是100％正確的。看看平面，這個平面旋轉了（1.0f，2.0f，0.0f），與紅色相比，紅色是顯示更高的曲面細分因子。綠色是1.0的因素。它應該在飛機的頂部更詳細，而不是底部。 
我錯過了什麼？
一些測試用例
如果我刪除旋轉的東西，它看起來像這樣： 
如果我刪除旋轉和我，包括這個簡單的版本orthogonale基礎計算的：
// simple version
sUp_.x = -camDirection.y;
sUp_.y = camDirection.x;
sUp_.z = camDirection.z;
sUp_.w = camDirection.w;
它看起來像這樣： 
難道它是一個問題，如果我不使用lookUp向量？ 你好嗎？我打開嘗試別的東西...