Animate uses a layer based keyframe animation system. For people who are not familiar with the creation of animation, this sounds complicated. It is a very quick and effective way of creating animation as the animator is just setting up guidelines for the computer to generate the majority of the frames.
A keyframe is essentially a frame of the movie. Within the frame you place objects where you want them to be. Every time you want to change the contents of the frame you create a new keyframe. This by itself is not that powerful. Where the power comes from is with tweening. Tweening is a method where you let the computer animate the object for you. The word tweening is a concatenation of the term “inbetweening” which is where the lead animator would draw the key frames and junior animators would draw all the frames between the keyframes. Animate has two types of tweening. Motion Tweening and shape tweening.
Motion tweening moves an object from the location it is on the starting keyframe to the location it is when it is on the ending frame. You can also apply rotation to the object that is moving. While technically not motion, you can also adjust any color adjustments (such as the alpha level) and the adjustment will smoothly transition between the frames. As objects in nature don’t move at steady rates, you can use leading to have the object start the motion at a faster rate and slow down as it approaches the end keyframe or have it start slow and speed up as it reaches the keyframe. The image below illustrates the difference between the three types of tweening.
For even more advanced animation effects, you can have guides. Guides let you specify the path that a moving object will follow. You can have the object follow the path while maintaining the same orientation or you can have the object orient itself to the path. My April Fool series of games has a title sequence where each letter has a winding path to it’s ultimate location. The screenshot below illustrates the different paths that the letters follow to reach their final location.
Shape tweening is a bit complicated. Shape tweening is when you have one shape and it transforms itself into the second shape. This is easy to do, but hard to do well. You simply need two shapes, a starting shape on the start keyframe, and an ending shape on its ending keyframe. To make sure the shape morphs the way you want, you add key points to the shapes. These points help Animate determine where the lines and points that make up the shape should line up after the end of the tween. Here is an example of a square turning into a star with the red shapes being the onion skin outlines of the frames between the square and the star.
An Animate movie consists of one or more layers. Layers go from back to front with closer layers overlapping further layers. Every layer is independent of the other layers. In other words, you can have keyframes in one layer but not any of the other layers. Animate lets you define as many layers as you need and lets you group the layers into folders. It is advisable to keep each animated object on its own layer as not doing so will result in animate creating a separate tween object in the library which often leads to problems.
The animation system is the primary reason why you would choose to create a game in Animate instead of creating it from scratch using the free Create.js libraries. While everything listed above can be done manually in Create.js, having a tool that generates all the source code for you is nice. If your game is a very heavy animation-oriented project, then using Animate makes sense.