WaveActiveCountBits function

Counts the number of boolean variables which evaluate to true across all active lanes in the current wave, and replicates the result to all lanes in the wave.

Syntax

uint WaveActiveCountBits(
   bool bBit
);

Parameters

bBit

The boolean variables to evaluate. Providing an explicit true Boolean value returns the number of active lanes.

Return value

The number of lanes for which the boolean variable evaluates to true, across all active lanes in the current wave.

Remarks

This function is supported from shader model 6.0 in all shader stages.

 

Examples

Although these are all equivalent, WaveActiveCountBits is the most efficient way to achieve this:

// Use WaveActiveSum to count number of active lanes
uint result = WaveActiveSum(1);

// Use countbits and WaveActiveBallot to count number of active lanes
uint4 bits = countbits( WaveActiveBallot( true ) );
uint result = bits.x + bits.y + bits.z + bits.w;

// Use WaveActiveCountBits to count number of active lanes
uint result = WaveActiveCountBits(true);

See also

Overview of Shader Model 6

Shader Model 6