Dynamic Tessellation - Practical Rendering and Computation with Direct3D 11 - page 437

Phase four, shown in Figure 9.20, is where the next big chunk of work takes place,
but before this, the group must have a plane from which to measure offsets, as shown in
Figure 9.19. This only requires a single thread and simply implements the plane-from-
point-and-normal equations, as shown in Listing 9.14.
// The following fragment of the compute shader uses
// this utility function:
float4 CreatePlaneFromPointAndNormal(float3 n, float3 p)
{
return float4(n, (-n.x*p.x - n.y*p.y - n.z*p.z));
}
// Phase 3 of the CS starts here:
if(GI == 0)
{
// Let the first thread only determine the plane coefficients
// First, decide on the average normal vector
float3 n = normalize
(
rawNormals[0][8]
+ rawNormals[0][1]
+ rawNormals[l] [0]
+ rawNormals[l] [1]
);
// Second, decide the lowest point on which to base it
float3 p = float3(0.0f,le9f,0.0f);
for(int i = 8; i < 2; ++i)
for(int j = 0; j < 2; ++j)
if ( corners [i][j].y < p.y)
p = corners[i] [j] ;
II Third, derive the plane from point+normal
plane = CreatePlaneFromPointAndNormal(n,p);
}
GroupMemoryBarrierWithGroupSync();
Listing 9.14. Phase three of the compute shader.
Figure 9.19. Compute shader phase three.