Slider Controls?

[Mike Clasby]

A slider lets you change a variable over time.

If you put an expression on Opacity (Alt Click the Opacity Stopwatch).

90

You get an opacity of 90 for that layer.

You could write it with a variable so you can see what you’re changing, like this:

op = 90;
op

Change the 90 and you change the expression and opacity.

But if you want to change the 90 over time, a slider is good. So Add a slider to the layer (Effect>Expression Controls>Slider Control), then in your earlier expression, highlight (select) the 90 and pickwhip (looks like an *, middle of those three little boxes) to the slider, to get:

op = effect(“Slider Control”)(“Slider”);
op

Now if you keyframe the slider over time, the slider will control the variable “op” and the opacity over time.

It’s really handy when you want to control several layer with the same expression. Add a slider to a Null, and this time lets name the Slider (double click it and rename) “Master Opacity”, from our original layer, pickwhip to that slider to get;

op = thisComp.layer(“Null 1”).effect(“Master Opacity”)(“Slider”);
op

Now if you wanted to apply that to many layers, highlight the expression (in original layer), and Edit>Copy Expression Only, then select as many other layers as you want, and Paste.

The slider “Master Opacity” in the Null will control all the layers’ opacity that have that expression.

Note: You can change the values on the Slider by putting your cursor over the value (on the slider) Right Clicking and Edit Value, then choose a new Min and Max between -1,000,000 and +1,000,000.
It’s often handy to change the values when you working with small numbers like between 0 and 1 , make 0 the min and 1 the max.

Sliders can be used for a lot more, anytime you want to change a variable, like here for turning Wiggle, On and Off (set the Frequency to 0):

freq = 5;
amp = 100;
wiggle (freq, amp)

But if you tied it to a slider, and set keyframes you can have it wiggle at a frequency of 5, then drop that to zero with slider keyframes. The slider expression for the above is this (Again with pickwhipping) and I named the Slider “freq” also:

freq = effect(“freq”)(“Slider”);
amp = 100;
wiggle (freq, amp)

It can be used in very interesting ways. Dan uses a slider here, Building the World’s Greatest Cameraman , to control what layer a camera looks at:

https://library.creativecow.net/articles/ebberts_dan/expression_cont.php

In the comp, “pan, tilt, focus, zoom”, the Point of Interest, of Camera 1, is controlled by the Slider in Null 1. Pretty nifty.

Aharon, a very clear a thorough, has a few tuts on expression controls, click his head on the main page and scroll down to:

Expression Controls #1, #2 and #3.

[Robert Till]

Thanks for the info. Very interesting stuff.