KS3 · Computer Science

Creating a 3D animation

Pause any animated film and you're looking at a still picture. So does an animator really pose every object in every frame? Almost never, and the trick is brilliant.

Computer Science · Algorithms

Trace table — dry run the code

A ball slides across the screen. The animator records just two keyframes. Step through and watch who fills in the rest. (Example frame rate: 10 frames per second.)

1// the animator records two keyframes

2KEYFRAME frame 0: x = 0

3KEYFRAME frame 10: x = 100

4// the software fills the gap

5step = (100 - 0) / (10 - 0)

6FOR frame = 1 TO 9

7 x = x + step

8 time = frame / 10

9NEXT frame

frame

time (s)

x

made by

Press Start to run the first line.

Ready when you are — step through one line at a time.

3D modelling · meshes

What a 3D object is really made of

Showing 4 layers: Faces, Edges, Vertices, Edited model

Layers

Explore

Turn the Faces layer off to see the cube as a wireframe, then explore each part.

The same cube after its four top vertices were moved inwards.

A 3D object isn't a solid lump. It's a surface built from points, lines and flat faces.

3D space · transformations

Move it, turn it or resize it?

Every object in a 3D scene sits in a space with three axes. In many programs x runs left–right, y runs up–down and z runs towards or away from you (some programs swap y and z, but there are always three). So every object has a position, a rotation and a size in three dimensions, and you change them with three transformations: translate (move), rotate (turn) and scale (resize). Tick every transformation each movement needs. Some need more than one.

A Translate (position)
B Rotate (rotation)
C Scale (size)

A toy car drives straight along a road
A planet spins on the spot
A balloon inflates
A ball squashes flat as it lands
A football rolls across the pitch
A rocket flies away and looks smaller and smaller
A logo spins while growing from tiny to full size, staying in the centre
A snowball rolls downhill, getting bigger as it goes
A ball changes colour from red to blue

Materials, lights and camera

Why does the shot look like that?

You've built a robot and rendered one frame. In the picture the robot is shiny and silver, it's brightly lit from the left, and you're looking at it from behind.

Where do those three things come from? Which idea is closest to what you think right now?

It's all part of the robot model. Its shape decides its colour, its lighting and which side we see.To see the robot's face, I'd have to turn the robot round.The brightness is part of the material. A shiny material lights itself up.The shiny silver comes from its material, the lighting from where the light is placed, and the back view from where the camera is.

How sure are you?

I'm sureI think soI'm guessing

It's all part of the robot model. Its shape decides its colour, its lighting and which side we see.

This is a common misconception

The mesh only gives the robot its shape. The shiny silver comes from the material applied to it, the brightness comes from a light placed in the scene, and seeing its back comes from where the camera is. Four separate things, and you can change each one without touching the others.

To see the robot's face, I'd have to turn the robot round.

This is a common misconception

You could, but you don't have to. The camera's position and angle decide what the viewer sees. Move the camera round to the front and you get the robot's face, with every object left exactly where it was.

The brightness is part of the material. A shiny material lights itself up.

This is a common misconception

A material sets the colour and surface qualities, like shiny, rough or patterned. How bright it looks depends on the lights placed in the scene. Move the light to the right and the very same shiny material would look bright on the other side.

The shiny silver comes from its material, the lighting from where the light is placed, and the back view from where the camera is.

This matches the evidence

Exactly. Materials and textures set the surface, lights placed in the scene light it, and the camera's position and angle decide what we see. Change any one of them and the render changes, even if no object moves.

Shape comes from the mesh. Colour and surface come from materials and textures. Brightness comes from the lights. What we see comes from the camera.

Rendering

How many frames does the computer have to draw?

Your finished clip is 12 seconds long and set to 25 frames per second (an example setting). Rendering means the software calculates every frame as a finished picture, using the models, materials, lights and camera. How many frames must it render?

Your estimate

300 frames

0 frames600 frames

Making it for an audience

Put the project in order

The order you would do these in when making a 3D animation for an audience

1 · Do this first6 · Do this last

Render the animation
Improve it
Build the scene: model the objects, add materials, lights and camera
Plan it: sketch the scene or storyboard the key moments for your audience
Test and evaluate the result against your plan
Animate it with keyframes

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

You set a few key moments. The computer works out every frame in between, and then draws every single one.

What you need to know

An animation is a sequence of still frames shown quickly one after another; the frame rate is how many frames are shown each second.
The animator records keyframes (an object's position, rotation or scale at chosen frames) and the software calculates the in-between frames.
3D objects are usually meshes made of vertices, edges and faces, often built by editing simple primitives.
Objects sit in a space with x, y and z axes and are changed by translating, rotating and scaling.
Materials and textures, lights and the camera set how a scene looks; rendering calculates every final frame from them.

The big picture

An animation is a sequence of still frames shown quickly, and the frame rate says how many are shown each second. In 3D animation the animator records keyframes and the software calculates the in-between frames. The objects are meshes of vertices, edges and faces, changed by translating, rotating and scaling them along the x, y and z axes. Materials, lights and the camera decide how the scene looks, rendering calculates every final frame, and the whole project is planned for an audience, then tested against the plan and improved.

Key points

1Frames are still images; showing them quickly creates the illusion of movement.

2Frame rate = frames per second, so frames needed = seconds × frame rate.

3Keyframes are recorded by the animator; in-between frames are calculated (interpolated) by the software.

4A mesh is a surface: vertices (points), edges (lines joining vertices) and faces (flat surfaces enclosed by edges).

5Translate changes position, rotate changes rotation, scale changes size, along the x, y and z axes.

6Moving the camera changes what the viewer sees without moving any object.

7Rendering can take a long time because every frame has to be calculated.

8Plan for your audience before you build, then test and evaluate against the plan and improve.

.we-_R_18slubsnpfiv5ubrb_ [data-we-step]{display:flex !important}.we-_R_18slubsnpfiv5ubrb_ [data-we-solution]{display:block !important}.we-_R_18slubsnpfiv5ubrb_ [data-we-reveal]{display:none !important}

Worked example

Problem

A door in your scene needs to swing open by 90° over 2 seconds. Your project runs at 24 frames per second, and the door starts closed on frame 0. Which frames should you make keyframes, how many frames will the software calculate, and what angle will the door be at on frame 24?

⚠ Watch out

Thinking the animator has to move the object on every single frame. The animator only records the keyframes; the software calculates all the frames in between.

🧠

Memory hook

You set the keys, the computer fills the gaps, then the render draws every frame. Keys → gaps → draw.

✓

Check yourself

A character's jump lasts 3 seconds at 20 frames per second. How many frames is that, which would you set yourself, and why does rendering it still take a while?

Flashcards

(12)

What is a frame?

One still image. An animation is a sequence of frames shown quickly one after another, which creates the illusion of movement.

What does the frame rate tell you?

How many frames are shown each second (frames per second).

What is a keyframe?

A frame where the animator records an object's position, rotation or scale.

Who makes the in-between frames, and how?

The software. It calculates (interpolates) them automatically from the keyframes on either side.

What are the x, y and z axes?

The three directions of a 3D space. Every object has a position, a rotation and a size along them.

What is a mesh?

The surface of a 3D object, made of vertices (points), edges (lines joining vertices) and faces (flat surfaces enclosed by edges).

What is a primitive, and how does it become a complex model?

A simple starting shape such as a cube, sphere or cylinder. You add it, then edit it (for example by moving its vertices).

Translate, rotate, scale: what does each change?

Translate changes position, rotate changes rotation (which way it faces), scale changes size.

Material or light: which gives an object its colour and shine?

The material (and any texture). Lights placed in the scene decide how brightly it's lit and from where.

What does the camera decide?

What the viewer sees, through its position and angle. Moving it changes the view without moving any object.

What is rendering, and why can it be slow?

The software calculating the final images from the models, materials, lights and camera, then outputting an image or video file. Every frame must be calculated.

What do you evaluate a finished 3D animation against?

Your plan (the sketch or storyboard you made for your intended audience).

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Trace table — dry run the code

Move it, turn it or resize it?

Why does the shot look like that?

How many frames does the computer have to draw?

Put the project in order

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