Tweening and motion

Hello students, welcome to Kwickprep. A cartoon shows twenty four pictures every second. Do animators really draw every single one by hand? Not anymore. Today we will learn tweening, the trick that lets the computer draw the in-between pictures for us, using Synfig Studio.

First, let us understand animation itself. Animation is a series of still pictures shown one after another, very quickly. Each single picture is called a frame. When each frame is only a little different from the one before, our eyes see smooth motion. The number of frames shown in one second is called the frame rate, measured in frames per second.

Think of a flip book in the corner of your notebook. On each page, you draw a ball a little further to the right. When you flip the pages fast, the ball seems to roll. But for a two second roll at twenty four frames per second, you need forty eight drawings. That is a lot of work.

This is where tweening helps. The word tweening comes from in between. You only tell the software where an object starts and where it ends. The software then calculates and creates every frame in between. So you save hours of drawing, and the motion comes out smooth.

Let us name the two kinds of frames. A key frame is an important frame where the animator fixes a position, like the ball at the left edge. The in-between frames are made by the software, showing the ball moving across. The last key frame, again set by the animator, has the ball at the right edge.

Tweening can change more than position. A motion tween changes the position, like a car driving across the road. A rotation tween changes the angle, like a spinning wheel. A scale tween changes the size, like a balloon getting bigger. A colour or opacity tween changes the look, like text slowly fading in.

Now, our software. Synfig Studio is free and open source software for making two dimensional animation. Open source means anyone can use it and see its program code, without paying. It runs on Windows, Linux and macOS. Synfig is built around tweening, so you rarely draw each frame yourself. Its files are usually saved with the extension dot sifz.

Synfig has two working modes. In normal mode, any change you make affects the object for the whole animation. In animation mode, a change is recorded at the current time only. You switch animation mode on with the button at the bottom right of the canvas window. When it is on, the canvas gets a red border, so you always know.

Four more words appear on the Synfig screen. The time slider lets you choose a moment in the animation. A waypoint is a value, like a position, saved at one moment in time. The timetrack panel shows these waypoints as small marks along a time line. The params panel lists the settings of the selected object, such as its origin, radius or colour.

Here are the steps to tween a ball. First, draw a circle at the left side of the canvas. Next, turn on animation mode. Then move the time slider to two seconds. Now drag the circle to the right side. Synfig saves waypoints at zero and at two seconds, and fills in every frame between them.

The software must decide how to fill the gap. This choice is called interpolation. Linear interpolation moves the object at the same speed all the way. Ease in and out starts slowly and ends slowly, like a car leaving and reaching a signal. Constant makes the object jump suddenly, with no in-between motion. Clamped is the default in Synfig, which gives smooth motion without going past the target.

Pause and predict. The ball is at zero at zero seconds, and at two hundred at two seconds. The interpolation is linear, so the speed is the same all the way. Where is the ball at exactly one second? It is at one hundred, exactly halfway, because one second is halfway in time.

Let us compare the two methods, a common exam question. In frame by frame animation, the animator draws every frame, but in tweening the software makes them. So frame by frame takes a lot of time, while tweening is quick. Frame by frame files are usually larger, and tweened files smaller. Frame by frame suits detailed acting, and tweening suits smooth, simple motion.

Let us revise what we learned today. Animation is many still frames shown quickly. Tweening means the software creates the in-between frames. You set the key frames, and the software fills the rest. In Synfig, changes made in animation mode are saved as waypoints. And interpolation decides how the object speeds up or slows down between them.