Computer Graphics

COMP3421/9415

2021 Term 3 Lecture 10

What did we learn last lecture?

A Deep Dive into Design and Art

• Some thoughts of Graphics and Art in general
• How Games are designed (and where graphics fits in)
• A look into the Art pipeline for digital assets

What are we covering today?

More detail on the Art Pipeline

• Continuing our overview of the Art Pipeline
• Going into a little more detail on:
• Modelling
• Rigging
• Animation

Developing a Character

Computer Games Art Pipeline

It's a long process from idea to polygons

• Concept
• Design
• Pre-Production (Technical Graphics appears here)
• Post-Production (iteration may involve redoing earlier steps)

Today, we're looking at Concept and Design

Various Production Images from Halo and Halo 2 (Bungie Studios and Microsoft 1999-2002)

Concept

We should have an idea of this now

• Have we given them a name? Should they have one?
• Is there any visual information yet? (probably not)
• Start doing research
• Visual References (start a pinterest board?)

Concept Art

Visual representations of ideas

• An early step in the design of a character (or location or vehicle etc)
• A lot of work will come from references here
• Very much the domain of the traditional sketcher/painter

Sculpting

Most likely digital sculpting

• Initial ideas going from concept art to 3D model
• Options for sculpting in clay and the 3D scanning
• More often sculpted and modelled digitally
• This work will be done in a 3D modelling and/or 3D sculpting program
• Unlikely to be game ready at this point
• Too many polygons to run efficiently
• Only vertices, no other important information

Programmers working with artists

In the meantime, us, the programmers are also working

• We'll establish a scale for the game world
• And most likely set up our source control (not always git when working alongside artists)
• Artists will provide us with a sample object (like a cube)
• We'll set up correct transforms for this and start building up graphics engine capabilities

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Optimisation and Texturing

Getting a model ready for use

• If a model has been sculpted, it might have a lot of extra polygons
• It will either be remodelled or optimised to remove vertices
• Then it must be UV mapped
• This is the process of adding texture coordinates to the vertices
• Texture coords are usually called (u,v)
• Then once mapped, actually "painting" the textures
• Creating the 2D images, usually in a digital painting program
• This also means adding other maps which we haven't learnt about yet in this course
• Artists might refer to these as "materials"

Polygon Reduction Optimisation

Image credit: Wikipedia

Rigging and Animation

Skin and Bones

• Animation in games is usually done via an internal bone system
• Artists will create a skeleton
• And "rig" the mesh to the skeleton
• With a rigged skeleton, animations can be created
• Animations are dependent on game needs, so they might not all be planned in advance

What ends up in the game?

As programmers we receive:

• A 3d model (vertex and index buffers)
• with textures and other maps (materials)
• and a set of animations

We will then:

• Make sure these are imported and handled in our engine correctly
• Transform the model into its correct place in the world
• Write code to activate its animations at the right time

How many artists was that?

There are many specialisations in this pipeline

• Concept Artists
• Sculptors
• 3D Modellers
• Texture Artists
• Riggers
• Animators
• Depending on the project, these might all be different people!

Modelling

Creating 3D Models

A big collection of vertices

• Models are essentially a bunch of verts
• (also textures and other maps/materials)
• Picking numbers for vert coordinates could be a very painstaking task
• So certain techniques are used to create multiple verts
• Box modelling
• Digital Sculpting
• 3D Scanning and Photogrammetry

Image credit: Stanford University

Box Modelling

Start with a box, add verts

• Start with some kind of primitive object (cube/cylinder are common)
• Add vertices in between
• Usually take a quad and turn it into 4 quads
• Move vertices around to create rough shapes
• The more verts you add, the more detail you create
• Common technique used in Maya, 3DS Max, Blender etc

Image credit: Diego Emanuel Viegas

Image credit: Don College

Digital Sculpting

Treating a 3D model like a solid substance

• Initially an attempt to give traditional sculptors a way to create digital models
• Adding and subtracting "chunks" of the model and smoothing with tools replicating real materials
• The concept of polygons and vertices does not drive the process
• but it will be a part of it eventually
• Used in Zbrush, Blender and others

Image credit: blenderartists.org user: 0rAngE

3D Scanning and Photogrammetry

Using technology to acquire surface information

• Laser scanners for detailed surface topography
• Cheaper and reasonably accurate results from photogrammetry
• Builds up 3D model automatically using relative viewpoints
• Usually very high complexity, would need significant reduction in polygons for use
• Marc's example: https://p3d.in/Ekkiv

Painting and Photogrammetry by Marc Chee

Break Time

The joys of creation

• Highly recommended to partake in art
• No limitations on what kind of art you want to do
• Something that takes you away from your "day job"
• Can be very valuable for stress relief and fulfilment
• Marc paints little toys in his spare time

Animation

What is animation?

A series of still images, an illusion of motion

• Oldest use of this is in Zoetropes (1800s or possibly 1st Century BC)
• The advent of film cameras and projectors brought the film industry to life (around 1895)
• We already understand the idea of frames and us drawing each frame as a separate still image
• But how do we decide how much our geometry should change between frames?

Image credit: William George Horner 1887

Image credit: Eadweard Muybridge 1887

Frame by Frame Animation

Doing it by hand

• The simplest way to understand
• Vertices are in a particular position in one frame
• They are in a new position in the next frame
• Hand drawn cel animation works in this way

Doing this in Graphics?

• While possible, it's incredibly time consuming, considering the number of vertices
• There must be a way of bulk editing multiple verts

Image credit: Jan-Eric Nyström, Helsinki, Finland

Vertices aren't alone!

Animation by objects

• We could animate by changing transforms!
• Each object can have its transform "lerped" maybe along a curve
• We could animate by changing some transforms within a scene graph
• This way, we could have different objects move relative to each other
• You may remember this from Tutorial 4 . . .

Animation by objects

What are the downsides to this approach?

• Forced separation of objects based on movement
• An artist will have to separately model fingers, lower arms, upper arms, shoulders etc.
• Models will start to look like deconstructed action figures
• Highly complex scene graphs and tiny separate pieces
• Computers can handle this, but can we?
• Also, how good is this method for say, an organic creature or cloth?

Skeletal Animation

An In-between solution

• What if we have ways of affecting sections of an object, but not the whole thing?
• Treat the mesh as the "skin" and build a skeleton inside the model
• The skeleton is a series of abstract positions that are linked together with a scene graph-like hierarchy of transforms

Images credit: Valve Developer Community

Details of Skeletal Animation

How do bones affect the mesh?

• Each vertex in the mesh is affected by some bone(s)
• We do this via a weighted list of bones in each vertex
• A simple rigid object might have a single bone and all verts are affected 100% by that bone
• A flexible are like the skin around an elbow will have partial weight from the lower arm and partial weight from the upper arm
• When a bone moves, it will alter the mesh
• The higher the weight, the more the mesh will follow the bone movement

Rigging

Rigging involves building a logical skeleton

• For something like a human, this is going to look reasonably familiar
• But for more abstract models, it's harder to predict
• Skeletons and bones don't have to be "inside" the mesh, they just control its movement and are hierarchically organised
• Each bone is intended to control some movement
• Vertices that are near that point of movement will be mapped to that bone
• Vertices further away will have less connection to the bone, or won't be connected at all

Rigging

Different weights will allow bones to have more influence over different parts of a mesh

Animation

Animate the Skeleton

• If we use the object based animation we talked about earlier
• But this time with the transforms in a rigged skeleton
• Our model will follow that skeleton
• It will also morph and stretch where there are partial weights
• It also means an animator is moving say 20-30 bones, not 500+ vertices

Keyframe Animation

Do animators specify positions for every frame?

• We've reduced the number of vertices, but not frames
• Skeletons usually only have translation and rotation relative to other bones
• Often animators will only set joint positions made up of rotation angles
• These poses can be used as "keyframes" and can be as little as one every 30-40 actual screen frames
• The frames in between can be determined by lerping the joint orientations

Keyframing Images

Images credit: Learnopengl.com

In OpenGL

Animating in OpenGL

• Import a model with animations, bone and weights
• Transform verts to their correct positions relative to bones
• Animations will have keyframe information
• As well as timings: How long in real time in between each keyframe
• To play an animation, we interpolate bone positions between keyframes depending on how long the animation has been running
• We transform vertices relative to wherever their bones currently are (and what weighting they have to the bones)

What did we learn today?

The Art Pipeline

• Overview of the entire art pipeline for something like a character
• Detail on 3D Modelling
• Detail on Animation and Rigging