如何将精灵渲染成真正的球体？

Question

我试图用液体效果渲染我的液体模拟器，

这是我的渲染结果：

但我希望得到这个结果

这是我的几何和像素着色器

[maxvertexcount(4)] 
void mainGS(point GSPS_INPUT gInput[1],inout TriangleStream<GSPS_OUTPUT> TriStream) 
{ 


  float size = 0.065; 
  matrix mv = View; 
  float3 right  = normalize(float3(mv._11,mv._21,mv._31));  
  float3 up    = normalize(float3(mv._12,mv._22,mv._32)); 
  // 
  float3 posEye = mul( float4(gInput[0].Pos.xyz, 1.0),world).xyz; 
  // 
  float halfWidth  = size/length(posEye); 
  float halfHeight = size/length(posEye); 
  // 
  float4 v[4]; 
  v[0] = float4(gInput[0].Pos + halfWidth*right - halfHeight*up, 1.0f); 
  v[1] = float4(gInput[0].Pos + halfWidth*right + halfHeight*up, 1.0f); 
  v[2] = float4(gInput[0].Pos - halfWidth*right - halfHeight*up, 1.0f); 
  v[3] = float4(gInput[0].Pos - halfWidth*right + halfHeight*up, 1.0f); 
  // 
  // 
  GSPS_OUTPUT output; 
  [unroll] 
  for(int i=0; i<4; ++i) 
  { 

    // 
    output.Pos    = mul(v[i], View); 
    output.PosW    = (output.Pos.xyz); 

    output.Pos    = mul(output.Pos, Projection); 
    output.Tex    = gQuadTexC[i]; 
    TriStream.Append(output); 
  } 
  TriStream.RestartStrip(); 
} 

//pixel shader 

float4 PS(GSPS_OUTPUT input) : SV_TARGET 
{ 
  float3 N; 
  N.xy = input.Tex*float2(2.0f,-2.0f) + float2(-1.0f,1.0f); 
  float mag = dot(N.xy, N.xy); 
  if (mag > 1.0)  
  { 
    discard; 
  } 

  N.z = sqrt(1.0f-mag); 
  N = N * 0.5 + 0.5; 


  float4 pixelPos = float4(input.PosW + N*(1/32), 1.0); 
  float4 clipSpacePos = mul(pixelPos, Projection); 
  float depthval = (clipSpacePos.z / clipSpacePos.w);

我在这里找到了这个，但它并没有完全解释 Link