Cg 3.1 Toolkit Documentation Cg / Standard Library / lerp

## Name

lerp - returns linear interpolation of two scalars or vectors based on a weight

## Synopsis

```float  lerp(float a, float b, float w);
float1 lerp(float1 a, float1 b, float1 w);
float2 lerp(float2 a, float2 b, float2 w);
float3 lerp(float3 a, float3 b, float3 w);
float4 lerp(float4 a, float4 b, float4 w);

float1 lerp(float1 a, float1 b, float w);
float2 lerp(float2 a, float2 b, float w);
float3 lerp(float3 a, float3 b, float w);
float4 lerp(float4 a, float4 b, float w);

half   lerp(half a, half b, half w);
half1  lerp(half1 a, half1 b, half1 w);
half2  lerp(half2 a, half2 b, half2 w);
half3  lerp(half3 a, half3 b, half3 w);
half4  lerp(half4 a, half4 b, half4 w);

half1  lerp(half1 a, half1 b, half w);
half2  lerp(half2 a, half2 b, half w);
half3  lerp(half3 a, half3 b, half w);
half4  lerp(half4 a, half4 b, half w);

fixed  lerp(fixed a, fixed b, fixed w);
fixed1 lerp(fixed1 a, fixed1 b, fixed1 w);
fixed2 lerp(fixed2 a, fixed2 b, fixed2 w);
fixed3 lerp(fixed3 a, fixed3 b, fixed3 w);
fixed4 lerp(fixed4 a, fixed4 b, fixed4 w);

fixed1 lerp(fixed1 a, fixed1 b, fixed w);
fixed2 lerp(fixed2 a, fixed2 b, fixed w);
fixed3 lerp(fixed3 a, fixed3 b, fixed w);
fixed4 lerp(fixed4 a, fixed4 b, fixed w);
```

## Parameters

a
Vector or scalar to weight; returned when w is zero.
b
Vector or scalar to weight; returned when w is one.
w
Vector or scalar weight.

## Description

Returns the linear interpolation of a and b based on weight w.

a and b are either both scalars or both vectors of the same length. The weight w may be a scalar or a vector of the same length as a and b. w can be any value (so is not restricted to be between zero and one); if w has values outside the [0,1] range, it actually extrapolates.

lerp returns a when w is zero and returns b when w is one.

## Reference Implementation

lerp for float3 vectors for a and b and a float w could be implemented like this:

```float3 lerp(float3 a, float3 b, float w)
{
return a + w*(b-a);
}
```

## Profile Support

lerp is supported in all profiles.