Hi-Z Screen-Space Cone-Traced Reflections - GPU Pro: Advanced Rendering Techniques - page 174

4.5.3 Ray-Tracing Pass
The implementation in Listing 4.5 is the Hi-Z ray-tracing code in Microsoft HLSL.
The code snippet is heavily commented and should be easy to follow once the
algorithm presented in Section 4.4.3 is clear.

float3 hiZTrace ( float3 p , float3 v )
{ const float rootLevel = mipCount −

1.0 f ; // Convert to 0
// based indexing

float level = HIZ_START_LEVEL ; // HIZ START LEVEL was

// set to 2 in the demo

float iterations =0.0 f ;

// Get the cell cross direction and a small offset to enter
// the next cell when doing cell crossing.
float2 crossStep , crossOffset ;
crossStep . x =( v . x > =0 ) ? 1. f : − 1. f ;
crossStep . y =( v . y > =0 ) ? 1. f : − 1. f ;
crossOffset . xy = crossStep . xy ￿ HIZ_CROSS_EPSILON . xy ;
crossStep . xy = saturate ( crossStep . xy );

// Set current ray to the original screen coordinate and
// depth.
float3 ray = p . xyz ;

// Scale the vector such that z is 1.0f
// (maximum depth) .
float3 d = v . xyz /= v . z ;

// Set starting point to the point where z equals 0.0f ( ←
minimum depth) .
float3 o = intersectDepthPlane ( p . xy , d . xy , − p . z );

// Cross to next cell so that we don ￿ tgetaself −

// intersection immediately.
float2 rayCell

= getCell ( ray . xy , hiZSize . xy );

rayCell . xy , hiZSize . xy , crossStep . xy , crossOffset . xy );

= intersectCellBoundary ( o . xy , d . xy , ←

ray

// The algorithm loop HIZ STOP LEVEL was set to 2 in the
// demo; going too high can create artifacts .
[ loop ]
while ( level > = HIZ_STOP_LEVEL && iterations < MAX_ITERATIONS ←
)

{

// Get the minimum depth plane in which the current ray
// resides .
float minZ = getMinimumDepthPlane ( ray . xy , level ,

←

rootLevel );

// Get the cel l number of our current ray .
const float2 cellCount = getCellCount ( level , rootLevel );
const float2 oldCellIdx = getCell ( ray . xy , cellCount );

// Intersect only if ray depth is below the minimum depth
// plane .
float3 tmpRay = intersectDepthPlane ( o . xy , d . xy ←
, max ( ray . z , minZ ));