dynamic visibility

solutions

• Static Potentially Visible Sets (PVSs)

  the world is discretised in some way (BSP, grid, etc.) and the binary visibility from each sector (leaf node, cell or cluster respectively) to all other sectors is pre-computed and stored. 动态物和一些可破坏物不在遮挡的计算范畴。

• Hardware Occlusion Queries

  rendering the depth of a subset (or a simplified representation) of the scene – the occluders – and then rasterising (without depth writes，with occlusion query) the bounds of objects, or groups of objects. 古老的技术，把物体的bounding box传入得到物体是否被遮挡的结果

• Hierarchical Z Buffer

  • Render Occluder Depth
  • Create a Depth Hierarchy

  • Test Object Bounds 根据投影到screen上的面积来决定depth map的mip level

    sampler2D sHZB : register(s0);
    
    float4 main(INPUT input) : COLOR0
    {
      float4 sbox    = input.sbox;
      float  level   = input.data.x;
      float  min_z   = input.data.y;
      bool   visible = input.data.z;
    
     float4 samples;
     samples.x = tex2Dlod(sHZB, float4(sbox.xy, 0, level)).x;
     samples.y = tex2Dlod(sHZB, float4(sbox.zy, 0, level)).x;
     samples.z = tex2Dlod(sHZB, float4(sbox.xw, 0, level)).x;
     samples.w = tex2Dlod(sHZB, float4(sbox.zw, 0, level)).x;
    
     // Modulate culling with depth test result
     float max_z = max4(samples);
     visible *= min_z <= max_z;
    
     return visible;
    }
    

  • Process the results 根据得到的visibility结果来决定是否剔除物体。