Creating A Sunrise Using Expressions : Adobe After Effects Tutorial

A CreativeCOW.net Adobe After Effects Tutorial

Mylenium
http://www.mylenium.de
Germany

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Article Focus:
The goal of this mini-tutorial is to show you some basic targeting using expressions as well as a few other tricks. Not only can this be used to create a stylized sun but also for lasers firing or wormholes.

Download the project files here.

Preface

The final result of this tutorial could also be achieved using manual techniques with 3D layers and a look_at expression. "So, what's the point then ?" you may say. Apart from my technique being largely automated once it is set up, there are several other things to consider:

a) 3D layers are slower than 2D layers, both while editing and when rendering.

b) Artifacts. Even though After Effects keeps getting better in 3D, it still is a rather weak tool for that kind of compositing. Even the advanced 3D renderer is far from being really advanced (nowadays it more like deserves the title "average" or "mediocre"). It's slow, has serious motion blur and anti-aliasing problems, causes quite often crashes (because it runs out of memory) etc..

c) There is a mathematical problem - at one point our layers are likely to show unwanted flipping if they were 3D. There are ways to avoid and compensate for it, but we will spare ourselves the trouble this time around.

That's why I try to avoid 3D in After Effects whenever possible and settle for 2D solutions instead.

Step 1: Setting up the project

Unlike in some of my other tutorials this is really simple this time. If you like, you can even do everything in one comp but I prefer to have two compositions - the main one called Sun and one separate comp for the Beam element. Apart from that, we only need to add two layers (or Null objects) to the main composition which will control everything. I named them Center and Target and Controller. Imaginative, isn't it? You can modify Center in any way you like and use it as the disc of the sun. The other layer will remain hidden and is really only used for animation and setting parameters. To keep things simple I only added a slider expression control and called it Radius.

Step 2: Beam me up Scotty

The look of the Beam is really very much a matter of your personal taste. The only immediate requirement is to make the composition 1000 pixels wide. This will simplify calculations later on. You may use other values, but I suggest to always use multiples of 100 (the reason why is explained in the Grid tutorial). Keep in mind that the more beams you use, the finer they should be. Now drop it into the main composition and set its anchor point to the leftmost edge.

Step 3: Expression time

The Beam layer uses expressions on all three standard transformation properties. First let's take a look at the position property.

center_X=thisComp.layer("Center").position[0];

center_Y=thisComp.layer("Center").position[1];

radius=thisComp.layer("Target and Controller").effect("Radius"("Slider");

my_angle=Math.PI*2/(thisComp.numLayers-2)*(index-2)-degreesToRadians(thisComp.layer("Center").rotation);

position_X=center_X+Math.sin(my_angle)*radius;

position_Y=center_Y+Math.cos(my_angle)*radius;

														
[position_X,position_Y]

What are we doing here? The position of a point on a circle can be expressed as functions of sines and cosines. Unfortunately the result of those is always somewhere between -1 and 1. Therefore we must multiply the results with the Radius from our Target and Controller layer and add the values to the position values of Center. Otherwise our sun would always stay in the top left corner where After Effects' coordinate system has its origin. Furthermore we are also taking precautions and already factor in a possible rotation of Center which we need to convert from degrees to radians. The circle itself is defined as a function of Pi. To split it into equal segments, we need to divide it by the number of layers in our comp (minus the two control layers).

The rotation is calculated very much as a standard targeting function:

diffX=position[0]-thisComp.layer("Target and Controller").position[0];

diffY=position[1]-thisComp.layer("Target and Controller").position[1];

myRot=radiansToDegrees(Math.atan2(diffY,diffX))-180;

[myRot]

The last expression is also the simplest one. The scale is calculated as follows:

[length(position-thisComp.layer("Target and Controller").position)/10,100]

And that's it! Now go ahead and clone the Beam layer a few times and see the sun shine into your life ;o).

Feel free to ask questions regarding this tutorial in the After Effects forum at Creativecow.net

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