3D Modelling and Animation
How 3D objects are built from vertices, edges and faces, how animation works with keyframes, and what actually happens when a scene is rendered.
How 3D models are built
The building blocks
| Term | Meaning |
|---|---|
| Vertex | A single point in 3D space, with x, y and z coordinates |
| Edge | A straight line joining two vertices |
| Face | A flat surface enclosed by edges, usually a triangle or a square |
| Mesh | The complete set of vertices, edges and faces making up an object |
A cube has 8 vertices, 12 edges and 6 faces. A detailed character model may have hundreds of thousands.
Polygon count
More polygons means more detail and smoother curves, and also more processing power and memory needed.
This is the central trade off in 3D work:
- A film can afford millions of polygons per character, because each frame is rendered once over hours
- A game must render 60 frames every second, so models are far simpler and use clever texturing to fake detail
Modelling techniques
- Primitives: start from a basic shape such as a cube, sphere or cylinder
- Extrude: pull a face outwards to create new geometry
- Subdivide: split faces into smaller ones to add detail
- Loop cut: add a ring of new edges around a model
- Modifiers: non destructive effects such as mirror, which builds one half and reflects it automatically
Coordinates
3D space uses three axes: x across, y depth and z height, though which is which varies between programs. Every vertex has a position, and every object can be moved, rotated and scaled along each axis.
Step 1 of 6 A vertex is one point in 3D space, with an x, a y and a z.
- A vertex is one point in space, with an x, a y and a z. A cube has 8.
- An edge is a straight line joining two vertices. A cube needs 12.
- A face is a flat surface enclosed by edges. A cube has 6.
- All of them together are the mesh, and that is the model.
- More polygons means more detail, and more work for the computer.
Materials, lighting and cameras
Materials and textures
A material describes how a surface behaves with light: its colour, how shiny it is, how rough, whether it is transparent or metallic.
A texture is an image wrapped onto the surface to give detail without adding geometry. UV mapping is the process of unwrapping a 3D surface flat so a 2D image can be applied to it accurately.
Textures are how a simple model gains detail cheaply. A brick wall can be a single flat face with a brick texture rather than thousands of individually modelled bricks.
Lighting
Lighting does more than make a scene visible. It creates mood and makes shapes readable.
- Point light, radiating in all directions from one spot, like a bulb
- Sun or directional light, parallel rays from far away, like sunlight
- Spot light, a cone, like a stage light
- Area light, a soft light from a surface, like a window
The classic setup is three point lighting: a bright key light as the main source, a softer fill light to lift the shadows on the other side, and a back light to separate the subject from the background.
Cameras
The camera decides what the viewer sees. Changing its position, angle and focal length completely changes how a scene feels. A low angle makes a subject look powerful, a high angle makes it look small.
- Three point lighting uses a key light, a fill light and a back light, and a camera frames the shot.
- The key light makes the shape, the fill light softens its shadows, and the back light gives it a bright edge.
Animation and rendering
Keyframes
An animator does not draw every frame. They set keyframes at important moments, and the software calculates the frames in between, which is called interpolation or tweening.
To move a ball from left to right over two seconds at 24 frames per second:
- Set a keyframe at frame 1 with the ball on the left
- Set a keyframe at frame 48 with the ball on the right
- The software generates the 46 frames between
Making it look right
- Easing means starting and stopping gradually rather than at constant speed, because real objects accelerate and decelerate
- Squash and stretch makes objects feel like they have weight
- Anticipation is a small movement in the opposite direction before the main action
- Follow through means parts keep moving after the main body stops
Rendering
Rendering is calculating the final image from the scene: working out how light bounces, what each surface looks like from the camera and what is in front of what.
It is extremely demanding. A single frame of a modern animated film can take hours on a powerful machine, which is why studios use render farms of hundreds of computers.
24 frames per second x 60 seconds = 1440 frames for one minute
At 30 minutes per frame that is 720 hours, which is 30 days on one computer.
A film renders each frame once, slowly, so it can afford perfect lighting and millions of polygons. A game must render every frame in under a sixtieth of a second while responding to the player, so it uses simpler models and approximations. The constraint is time, not talent.
- Keyframes are the key moments the animator sets. The computer works out the frames in between, which is called interpolation or tweening.
- Linear motion has constant speed. It starts and stops suddenly, which looks like a machine.
- Easing starts and stops gradually, because real objects speed up and slow down.
Key terms you must be able to define
- Vertex
- A single point in 3D space defined by x, y and z coordinates.
- Edge
- A straight line connecting two vertices.
- Face
- A flat surface enclosed by edges, forming part of a model's surface.
- Mesh
- The complete set of vertices, edges and faces that make up a 3D object.
- Polygon count
- The number of faces in a model, affecting both detail and performance.
- Texture
- An image applied to a surface to add detail without adding geometry.
- UV mapping
- Unwrapping a 3D surface flat so a 2D texture can be applied accurately.
- Keyframe
- A frame where the animator sets a value, with the software calculating the frames between.
- Interpolation
- The software generating the in between frames from the keyframes.
- Rendering
- Calculating the final image from the 3D scene, including light, materials and perspective.
Flashcards
Say the definition out loud before you flip the card. Retrieving it from memory is what builds recall, reading it again is not.
Reach the top grade on this topic
The top level here is about explaining trade offs.
Polygon count is always a trade off. More polygons means more detail and more processing. Say both halves.
Explain why textures matter. A texture adds visible detail at almost no performance cost, which is why a brick wall is one flat face with an image on it rather than thousands of modelled bricks.
Explain rendering time with a calculation. Frames per second multiplied by duration gives the number of frames, and multiplying by time per frame shows why render farms exist.
Justify lighting choices. Three point lighting is not a rule to memorise. The key light provides the main illumination, the fill lifts the shadows so detail is not lost, and the back light separates the subject from the background.
- Define vertex, edge, face and mesh and give the counts for a cube
- Explain the trade off in polygon count for a game against a film
- Explain how keyframes and interpolation produce animation
- Calculate the total render time for a given length of animation
Mistakes that cost marks here
- Saying more polygons is simply better. It costs performance, which matters enormously in games.
- Confusing a material with a texture. A material describes how the surface behaves with light, a texture is an image applied to it.
- Thinking every frame is animated by hand. Keyframes are set and the software interpolates.
- Saying rendering is 'saving the file'. It is calculating the image, which is why it takes so long.
Every 3D model in every film and game is made entirely of flat triangles. Curved surfaces do not exist. They are thousands of tiny triangles arranged so the edges become invisible.
Knowledge check
Exam-style questions
Five written questions in the style of the real paper. Write a full answer, then let the marker check it against the mark scheme.
- LA vertex is a point in 3D space
- LAn edge is a line connecting two vertices
- LA face is a flat surface enclosed by edges
A vertex is a single point in three dimensional space, defined by its x, y and z coordinates. An edge is a straight line connecting two vertices. A face is a flat surface enclosed by edges, usually a triangle or a four sided shape, and together the vertices, edges and faces form the mesh that makes up the object.
- LA game must render frames in real time as the player plays
- LAround 60 frames must be produced every second
- LA film renders each frame once in advance, taking as long as needed
- LFewer polygons means the game runs smoothly, with textures used to suggest detail
A video game has to produce each frame in real time while the player is controlling the character, which means the computer typically has less than a sixtieth of a second to work out lighting, positions and surfaces for the entire scene. If a model contains too many polygons the machine cannot keep up and the frame rate drops, which makes the game feel unresponsive and unplayable. An animated film has no such constraint, because each frame is rendered once in advance and can take minutes or even hours on a render farm, so millions of polygons per character are affordable. Game artists therefore use much simpler meshes and rely on detailed textures and lighting tricks to suggest detail that is not actually modelled, which costs almost no performance while looking convincing on screen.
- LThe animator sets values at particular frames
- LThese are the keyframes marking the start and end of a movement
- LThe software calculates the frames in between by interpolation
Rather than creating every single frame by hand, the animator sets the position, rotation or other property of an object at a small number of important moments, and each of these is recorded as a keyframe. For example, a keyframe at frame 1 might place a ball on the left of the screen and a keyframe at frame 48 might place it on the right. The software then calculates all the frames in between automatically, a process called interpolation, gradually changing the value from one keyframe to the next. The animator can adjust how that change happens, for example using easing so the movement accelerates and slows rather than travelling at a constant speed, which looks far more natural.
- LCalculates the number of frames as 25 x 90
- LObtains 2250 frames
- LMultiplies by 4 minutes to get 9000 minutes
- LConverts to 150 hours
The total number of frames is the frame rate multiplied by the duration, so 25 x 90 = 2250 frames. Each frame takes 4 minutes, so the total render time is 2250 x 4 = 9000 minutes. Dividing by 60 converts this to 150 hours, which is over six days of continuous rendering on a single machine, and this is exactly why studios use render farms of hundreds of computers working on different frames at the same time.
- LA texture is an image applied to the surface of a model
- LIt adds visual detail without adding polygons
- LThis keeps the model efficient while still looking detailed
A texture is a two dimensional image that is wrapped onto the surface of a 3D model, using UV mapping to ensure it lines up correctly on a curved or complex shape. Its purpose is to add visual detail such as wood grain, brickwork, rust or fabric weave without adding any extra geometry to the model. This matters enormously for performance: modelling every individual brick in a wall would require an enormous number of polygons and slow the scene down, whereas a single flat face with a brick texture looks convincing and costs almost nothing to render.