Where WeÕve BeenÉ Éugweb.cs.ualberta.ca/~c250/F07/schedule/lectures/Lecture10.pdfRendering CMPUT...

History of Technology in Games3D Graphics

CMPUT 250

Fall 2007

Tuesday, October 9

CMPUT 250: Fall 2007 Lecture #10: History 3

Where We’ve Been…

! Processing

! Storage

! Graphics

! CRT

! Vector Graphics

! Raster Graphics

! Bitmaps

! Resolution, Colour Depth, Frame Rate

! Early Arcade Games Raster Wins


…

! 2D Graphics

! Sprites

! Layers

! Collision Detection

! Specialization and Generalization

! History of Home Consoles


Today

! 3D Graphics

! Camera

! Meshes

! Triangles

! Models

! Culling

! Volume Partitioning

! Advances in 3D

! Shading and Texturing

! Special Effects


3D Graphics

! This is a very complex subject

! Video screens are 2D; World is 3D

! Produce a 2D image of a 3D world

! Virtually build our 3D world

! Point a virtual camera at it

! How do we describe the objects in the world?

! What does our camera do?

Scene

Rendering


Types of Rendering

! Non Real-Time (e.g., raytracing)

! Trace paths of beams of light in the world and computetheir colour when they hit the camera’s field of view

! Slow (minutes or hours for one frame) but high quality

! Used in movies like Pixar’s Toy Story, etc.

! Sometimes used to pre-render scenes in games

! These images can also be used as a background

! Real-Time

! Draw image in real-time (quickly enough to animate)

! Lower quality but world can change with player actions


! A camera is a view of the world

! Occupies a position in 3D space (x,y,z) and pointsin a direction

! Viewing angle (horizontal and vertical)

! Real cameras also have:

! Focal length

! Lens Distortion

! Focus

! Depth of Field

The Camera


The Camera: Frustum

! Volume visible to camera: view frustum

© George Otto, Penn State University


The Camera: Styles

! Fixed cameras

! Finite position and direction (Myst, 7th Guest)

! Fixed position (Myst 3)

! Fixed direction (some RTS, isometric view)

! Fixed path (rail-shooters like Virtua Cop)

! Fixed path with free direction (rail-shooters like

Panzer Dragoon)


The Camera: Styles

! Free cameras

! Chase camera (3rd person, follows behind)

! Free-look (1st person, looks wherever you point)

! Look-spring (1st or 3rd camera can be moved butautomatically returns to its default when released)

! Rear-view (look behind you)

! Droppable (move and then leave it there)

! Switching from 1st to 3rd or vice versa


The Camera: Friend or Foe?

! Obstructions in 3rd person view

! Where does the chase camera go when you

back into a wall?

! Camera won’t allow the angle you want

! Camera too slow

! Camera too erratic or has jerky transitions

! Camera too automatic or too manual


Simple “3D” Tricks

! Scaling: making 2D sprites bigger or smaller tosimulate moving toward or away

! Boot Hill (Midway, 1977)

! Isometric view: 2D artistic style showingperspective from a fixed angle

! Zaxxon (Sega, 1982)

! These aren’t really rendering

! We want a world with real 3D objects (i.e., they occupysome volume of space… not just an area of the screen)


The Scene

! Need to represent things in the world

! Irrelevant what they look like inside

! Let’s make “hollow” objects

! Here’s the plan:

! Objects defined by surfaces (or meshes)

! Surfaces built out of polygons

! Polygons built out of triangles

! Triangles defined by their vertices


Polygons

! Polygons are 2D objects described by three

or more points connected by line segments.

! They are closed (all line segments

connected) and line segments do not cross

each other.

! A point used to describe a polygon is called

a vertex (plural: vertices).


Example of Polygons


Examples of Non-Polygons

Not line segments

Not closed

Line segments cross


Triangles

! Simplest polygon

! Nice mathematical properties

! Can divide up more complex polygons into

triangles (tessellation)


Coordinates

! Two dimensional points can be described using2D coordinates or vertices

! Each coordinate is two numbers (x and y), referring tohorizontal and vertical position

! For our surfaces, we must use 3D coordinates(x, y, z) referring to horizontal, vertical, and depth

! Our polygons (triangles) will be described by 3Dcoordinates


Meshes

! A collection of triangles for a single

“object” is called a mesh

! In the end, a mesh is just a big list of vertex

coordinates


Multiple Meshes

! Figures can be composed of multiple

meshes. The pieces (meshes) can separate.


Normal Vectors

! Recall our objects are hollow and we only

care about the “outside”

! Which side is the outside?

! Normal vectors point out from a triangle’s

visible side


How to Draw a Scene

! World is built out of many, many triangles

! Place the camera in the world

! We can calculate what a triangle looks like from thecamera’s position

! But some triangles obscure others (?)

! One idea:

! sort triangles by how far away they are

! draw them from furthest to closest

! closer triangles will be drawn over top of furthertriangles


Problem

! Too many triangles

! Limited number can be drawn per frame

! Essentially the same problem we had in vectorgraphics and sprite graphics

! Always need to consider scene complexity

! Many factors to complexity

! Number of potentially visible triangles

! Effects in rendering those triangles

! How can we draw complex worlds?


Culling

! Reduce the number of triangles we need to draw

! Culling is the process of eliminating trianglesfrom the list of those we need to draw.

! Can obviously ignore

! triangles behind the camera

! triangles out of the forward field of view up-down andright-left

! triangles beyond the camera’s range

! all this is called frustrum culling

! only consider triangles inside the camera’s frustrum


The Camera: Frustum

! Volume visible to camera: frustum

© George Otto, Penn State University


Clipping

! Only considering triangles inside the

frustum now

! Triangle may only be partially inside

! Cut off part of triangle that is outside

! This process is called clipping


Still have problems…

! With complex worlds, even computing what

triangles are inside the frustum may be too slow!

! Camera’s max depth may cover most of the world

! Need a fast way of deciding what triangles might

be visible before we cull

! Let’s break the world up into manageable spaces


Philosophical Question

Ever wonder why you can’t just

blow any and every wall up?


Static vs. Dynamic Objects

! Static Objects, e.g., walls, statues, trees

! Precompute (calculate ahead of time) and store

information about the visibility of its triangles

! Use the information to speed up rendering

! If most of the world is static… life is good

! … but boring

! Static objects can still help


Volume Partitioning

! Use static objects to divide up (partition)

the world into separate spaces (volumes)

! Rooms are a natural way to do this

! We can manually specify the division when

we design the levels

! There are more automatic methods, but we

start with a portal system.


Portals

A

B

CD

A B C

D


Portals

! Divide world into regions connected by

portals

! Camera is limited to triangles in the same

region as it (or adjoining regions)

! Allow portals to be open or closed to keep

the number of regions small

CMPUT 250: Fall 2007 Lecture #10: History 3 CMPUT 250: Fall 2007 Lecture #10: History 3

Automated Volume Partitioning

! Automated methods split the world’s

volume up into pieces using geometry.

! Examples include

! Binary space partitioning

! Quadtrees

! Octrees

! Many games use a mixture of manual and

automatic methods


Early 3D

! Made possible by volume partitioning

! 2D graphics (sprites) in a 3D environment

! The Games

! Ultima Underworld (Looking Glass, 1992)

! Wolfenstein 3D (id Software, 1992)

! Doom (id Software, 1993)

! Heretic (Raven Software, 1994)

! Marathon (Bungie, 1994)

! System Shock (Looking Glass, 1994)

! Duke Nukem 3D (3D Realms, 1996)


Early 3D: 2.5D

! One “floor”: possibly variable height

! No rooms above rooms (except by trickery)

! History

! Ultima Underworld allowed a complex environment(angled walls, inclined surfaces) but was slow

! Wolfenstein 3D made simplifying assumptions (e.g. all-right angles, all floors the same level) and was fast

! Doom relaxed restrictions (some angled walls, somevariable height floors) while keeping the speed

! Heretic allowed angling viewpoint up and down


Early 3D: Beyond 2.5D

! More History:

! System Shock broke 2.5D and allowed floors above

other floors and transparency (although slow)

! This functionality might have been around in Ultima

Underworld

! But, the id games were ultimately more successful

! Simpler

! Faster


System Shock (Looking Glass, 1994)

© MobyGames


Doom (id Software, 1993)

© MobyGames


Models

! Sprites look weird in a 3D world!

! We need 3D objects

! Game creatures, power-ups, doors

! Destructible parts of environment

! These are sometimes called models to

distinguish them from static background


Models

! Meshes!

! Lots of triangles per model, though

! Can’t precompute anything

! Limit number of visible models

! Keep track of where model is in volume partitioning

! Ever notice that sprite-based 3D games had many,

many enemies. In polygon-based, not so many


Quake (id Software, 1996)

© MobyGames


Later 3D: Sprites Replaced

! Descent (Parallax, 1995)

! Quake (id Software, 1996)

! Quake II (id Software, 1997)

! GoldenEye 007 (Rare, 1997)

! Half-Life (Valve, 1998)

! Thief (Looking Glass, 1998)

! Unreal (Epic, 1998)

! System Shock 2 (Irrational Games/Looking Glass,1999)


Modern 3D: Graphics Hardware

! Early 3D games used software rendering

! Up to around Quake II (1997)

! Computed entire process on the general-purpose CPUSprite hardware only semi-useful

! 3D hardware rendering was very expensive

! Developed by Silicon Graphics (SGI) throughout thelate 80’s and 90’s

! Commercially viable for home gaming startingwith the Voodoo card from 3dfx in 1996


Modern 3D: GPU

! Much of 3D is repetitive calculations

! Custom hardware can do this more

efficiently than the general-purpose CPU

! Graphics Processing Unit (GPU)

! Initially, vertex information computed by CPU

and sent to GPU to draw with textures


Modern 3D: GPU

! More and more features added to GPUs

! Hardware transform and lighting

! Complex texturing operations

! Completely programmable “pixel shaders” –

more like a traditional CPU!

! Sound familiar?

! Expect to see physics and collision

detection soon!


Rendering Triangles

! Now we know what triangles to draw

! How do we draw them?

! A little math figures out what the triangle’s

shape is from the camera’s perspective

(transform)

! What do we draw?


Rendering: Wireframe

! Just draw the lines: wireframe

© www.realityfactory.ca


Rendering: Filled

! Fill triangles with a single, solid colour

! Soecify colour for each triangle with RGB

values

! Problem: adjacent faces of

the same colour indistinguishable

© www.realityfactory.caCMPUT 250: Fall 2007 Lecture #10: History 3

Rendering: Flat-Shading

! Draw filled triangles shaded according to light

! Flat-shading

! Specify colours for triangles

! Specify light(s)

! Compute effect of light

on filled triangles

! Single (but different) colour

for each triangle

! Gives a proper 3D impression, but crude



Rendering: Smooth-Shading

! Shade each triangle according to lights

! Smooth-shading

! Colour varies over triangle

! Smoother transitions between

adjacent triangles

© www.realityfactory.caCMPUT 250: Fall 2007 Lecture #10: History 3

Rendering: Texturing

! Fill triangles with an image

! Texturing

! Specify entire image for surface

(i.e., a colour for every pixel)

! Texture pixels called texels

! Can shade texels according

to light as well

! Texture mapping: stretch image

over an entire mesh, instead

of just a single triangle



Texturing Issues

! Texturing adds a huge amount of realism

! Can add surface detail without adding triangles

! Textures can even be animated (i.e., change theimage over time)

! However, requires much more storage thanshaded triangles

! A huge part of modern gaming technology isconcerned with allowing more textures, withhigher resolution, and moving texture informationaround efficiently


Texture Resolution

! If you get very close to a texture, it may look“blocky” because you can see individual texels

! Far away objects don’t need much detail

! Standard solution: mipmapping

! copies of same texture at multiple resolutions

! switch copies as camera moves further/closer

! Switching resolutions can cause odd problems

! partially solved by filtering: bilinear, trilinear,anisotropic


Level of Detail

! Mipmapping is an example of a level of detail

(LOD) approach

! Basic idea is that far away things need less detail

! Other LOD approaches, include

! Changing meshes at different distances (fewer triangles

when far away) (e.g., “Messiah” by Shiny, 2000)

! Dropping lights, shadows, and any other special

features when objects are far away


Advanced 3D

! It’s all about the effects

! What about windows?

! What about fog or mist?

! What about smooth versus rough surfaces?

! What about shiny surfaces?

! What about mirrors?

! What about water or fire?

! What about realistic clothing or hair or fire or smoke?

! What about shadows?


Transparency

! Colour the light that passes through translucent objects

! Do this by adding an extra value to every pixel (texel)

! Red, green, blue, and alpha

! Alpha specifies how transparent the pixel is

! When drawing the scene, transparent pixels modify thevalue of stuff behind instead of overwriting it

! Keep in mind that transparency means more visibletriangles!


Lights

! Another very complicated subject

! Basic properties

! Intensity (brightness)

! Colour

! Source

! Advanced properties

! Diffusion, specular highlights, reflection


Kinds of Light

! Ambient light

! Artificial concept of light that is “everywhere” in thescene – all surfaces are lit by it equally

! Everything is visible to some minimum extent

! Point-source lights

! Placed in the world (like the camera)

! Shine in all directions

! Directional lights

! Placed in the world (like the camera)

! Shine in a cone


Diffuse vs. Specular Lighting

! Diffuse lighting refers to surfaces absorbing andthen emitting light uniformly over the surface

! Angle of incoming light matters

(affects quantity of emitted light)

! But viewer’s angle does not

! Specular lighting “bounces” off the surface

! light comes in at an angle and leaves at an angle

! viewer’s angle matters

! responsible for “shiny spots”

or “glare” on objects


Specular Highlights


Reflectivity

! The reflectivity of a material determines how

much light is absorbed versus reflected.

! Highly reflective surfaces create reflections

! Parts of the scene appearing in shiny surfaces

! Expensive to do properly, so faked instead


Environment MappingCube Map

© www.developer.com CMPUT 250: Fall 2007 Lecture #10: History 3

Environment MappingCube Map

© Stephen Chenney, U. Wisconsin


Precomputing Lighting

! If lights are static, we can precompute their

effect on a surface and store it

! The stored information is called a lightmap

! Combined with the texture of a surface

during rendering to change its look


Lightmaps

+ =

Texture Lightmap Rendered surface

© www.flipcode.com

! Reuse textures with different lightmaps

! Saves space


Bump Mapping

! A per pixel lighting effect

! Each pixel specifies its own surface normal

! Light is bounced off each pixel relative its

individual surface normal

! Great for adding roughness to surfaces


Bump Mapping

CMPUT 250: Fall 2007 Lecture #10: History 3 © www.earthenrecords.com

Halo (Bungie Studios, 2003)

CMPUT 250: Fall 2007 Lecture #10: History 3 © www.earthenrecords.com

Halo (Bungie Studios, 2003)


Bump Mapping: Angle Sensitive

© www.earthenrecords.com


Lighting: Finer than Triangles

! So far, lighting behaviour specified for each triangle

! Contemporary lighting doesn’t stop at triangles

! Lighting can be per vertex

! Lighting specified for each vertex and “blended” over the triangles

! Lighting can be per pixel

! Each pixel on the surface specifies its own lighting behaviour


Materials

! We seem to be collecting a lot of information to describetriangles

! Information about drawing triangles is often calledmaterial information

! Colour/texture

! Transparency (alpha)

! Reflectivity

! Special effects (e.g. bump mapping info)

! Precomputed effects (e.g. light maps, shadow maps)

! Games are using more and more detailed materialinformation – it all costs storage!


More, more, more

! Pixel shaders

! Shadows

! Particle effects

! Cel-shading

! 3D Collisions

! More realism… more hardware


In Summary…

! 3D graphics is a very complex subject

! Video screens are 2D; World is 3D

! Produce a 2D image of a 3D world

! Virtually build our 3D world

! Point a virtual camera at it

! How do we describe the objects in the world?

! What does our camera do?

Scene

Rendering


Questions?


Post Mortems

! A critical examination of the game design

process and the resulting final product.

! What went right?

! What went wrong?

! By the designers!

! They know their design goals.

! They know the process and decisions that went

into their game.


Why Post Mortems?

! The process is good for the designers.

! Critically analyze the design process.

! Identify mistakes to be avoided in the future.

! Can also benefit other designers.

! Inside track on their design goals and process.

! Learn from others mistakes.


Katamari Damacy (2004)

Where WeÕve BeenÉ Éugweb.cs.ualberta.ca/~c250/F07/schedule/lectures/Lecture10.pdfRendering CMPUT...

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