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All animateable parameters in Electric Image Animator are numeric values that - when animated - change over time. The standard method to do so is to set keyframes and to design their interpolation with function curves. However, there are many animation tasks where this approach is very limited or certain results are simply not attainable.
An example for such a task is the spinning of a wheel on a car. The car moves along and the wheels rotate dependent on the distance the car travels. With keyframed animation you have to figure out how fast the wheel has to rotate in order to behave naturally. You will figure out a math formula and calculate the rotation of the wheel for a certain distance. When you have set your keyframes for your wheels you have the trouble that accelerating and decelerating of your car will have to reflect in the speed of the wheels. So whenever you change the animation of the car you have to adjust the rotation of the wheels afterwards to get them right. What if a program would do this automatically for you?
Programable expressions are the ultimate solution. An expression is a math formula that executes on each frame when the animation is playing. Since every animateable parameter within Electric Image Animator is a number it can be calculated. In our example this means that the expression calculates the rotation of the wheels based on the distance the car travels automatically. All you have to do is to find the math formula that describes the dependency of the wheel rotation to the distance the car travels - which you had to figure out anyway, also with keyframed wheels.
Expressions are also great for repetitive and oscillating stuff like blinking lights and so on. Since the time position in your animation is only a value, you can setup expressions that are driven by the time value. This enables you to do entire animations without setting a single keyframe!
This may sound complicated but it isn't as much as you may think.
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