This is a simple but very useful equation to blend between two values A and B.

( A * w ) + ( B * ( 1 – w ) )

w is a ** weight **value.

When w = 0 the answer is B,

and when w = 1 the answer is A.

( A * 0 ) + ( B * ( 1 – 0 ) ) = A

( A * 1 ) + ( B * ( 1 – 1 ) ) = B

This equation is used all over computer graphics. It the basis of compositing pixels, and can be used to make controls for technical animation ( see this eye rig setup for 3dsMax )

## Tutorial: Using the maths as an expression in Eyeon fusion.

In this tutorial I use an expression script to animate a blend between two changing positions. This allows the creation of a new point based on the current position of two other points.

You can download a sample file here

## Note: using * in algebra …

The convention is write equations concisely without the * for multiplication like this:

A w + B ( 1 – w )

This is because hand written algebra tends to use single letters for variables, and multiplication signs can get confused with the variable **x**. While this form is easier to read, it can be confusing were people are used to reading computer code, and are expecting * for multiplication and long variable names.