Game Engines Part 1
Introduction
Everybody loves to play games and enjoy features like the
story, art or even combat mechanisims, but then there’s others like to reflect
on how well the game’s been produced in terms of graphics, sound and maybe even
non-playable characters. In reality we are too consumed in the game itself to
even dwell up the masterpiece of the game engine itself and how it can be
considered the heart of the game?
The Purpose
So what exactly is a game engine, its purpose and how it
differs from a ‘game’ itself? Basically a game engine is a system designed for
the creation and development of video games. The leading game’s engines provide
what’s called a software framework that developers use to create games for
various platforms like consoles, computers and mobile devices. An engine is a
set of tools and mechanisms prepared separately to add in eventually as the
engine is being built, meaning that every engine’s code and scripting is unique
and can’t be re-used- hence why game engines take a considerable amount of time
to develop. Now the framework is a code base that handles important aspects of
games such as hardware interfacing and input, always coming with a
predetermined rule set. A game however is a piece of media entertainment that
runs from a game engine, but includes other pieces as well like
design/story/art design features and can be played as well.
For example we can’t start making a game engine until we
actually focus on the concept (or more like the game design
document/pre-production document) of what the game is going to be about. Until
it’s decided and both documentations have been completed and cleared it’s then
we can move onto modelling and assets and then onto building up the game engine
itself, which is why there can be a huge debate on what could be considered as
the heart or the most important piece of a game.
Difference between Engines
As we know gaming itself, has developed a lot over the
years, which means the game engines themselves have come to produce more
realistic effects and have branched out to other devices that’s been urbanized,
e.g mobile phones, tablets.
One of the earliest game engines is NovaLogic’s Voxel space
engine. It managed to combine volumetric and pixels, thus creating 3D bitmap
images rather vectors. In the early 90’s it was used mainly for flight
simulators, also managing to render command and conquer vechiles. A good
example of a game that used this engine is games like Quebert and even
Minecraft.
In 1996 ID Tech produced the first amazing 3D engine that
was brilliant at rendering methods, allowing pieces like brushes and
z-buffering to be visible. It also used a certain scripting known as QuakeC,
again another game that used this is Team Fortress. However the company decided
to develop their engine further. In 1999 they introduced shaders, curved edges
and network capabilities meaning that rendering itself became increasingly
difficult but more of a masterpiece until 2004 when ID Tech 4 appeared. Back
then it was considered to be a groundbreaking engine development, able to last
through code overhaul and switching from C to C++. ID Tech has so far managed
to bring out a number 5 of their series that allows volumetric lighting, post
processing, virtual texturing and HDRR (High Dynamic Range Rendering). Upcoming
games using this are Wolfenstein: The
New Order and Doom 4.
It also managed to add more realism to the graphics itself
with the lightning and depth compared to an equally successful engine called
GameByro (developed in 2003). GameByro was a successful multi-platform engine
that had created a great dynamic collision detection and particle system- in
which games like Fallout 3 and Oblivion took hold of.
In 2004 two powerful engines were produced known as Source
and CryENGINE. Source became the follow on from GoldSRC( known in 1998 for its
written C++ to make a cross platform
features in Half-Life and Counter Strike), adding more shaders, dynamic
lighting, reflective water and real time motion blur. It was though heavily
modded meaning it had to be constantly updated. As the original Half-Life and
Counter Strike used its predecessor, there’s no surprise as to why Source
became the target engine for their sequels. CryENGINE compared to Source became
a very demanding piece of technology reliant on high visuals and hardware,
which added more beautiful graphics to players maybe being the reason as to why
Far Cry and Crysis where big hits back in that time. Nowadays CryENGINE has
become an even bigger success, unlike Unreal the engine is addictive adding
more to the level design and world of the game rather than hindering it or
simply taking away the ‘perfect’ effect.
CryENGINE 3 uses a WYSIWYP approach which is what most game interfaces
use adding more of an advanced lighting, particle system, normal maps and
modular AI system.
Even though CryENGINE has seemed to have won the battle of
the better gaming engine, Unreal 3 was not something to be frowned upon in the
2007 era. Considered to be the most popular and well-known game engine, known
for its multi-platform and its DirectX 10 compatibility games like the Mass
Effect series, Devil May Cry and Batman Arkham City used this. Since then the
Unreal engine series has a number 4 that promises to use real time global
illumination and voxel cone tracing soon to be present in games like Fable
Legends, various MMORPG’s, Project Awakened and Fortnite.
Speaking of famous titles if we look at Battlefield 3, Medal
of Honour and Need for Speed, we can see
the engine company known as: Frostbite, uses a heavy shader engine making it
graphically impressive giving off multiple shaders. It also allows players to
witness destructible environments as well as being multi-platform compatible
since 2008. Upcoming titles that plan to use this engine still are Dragon Age:
Inquisitor, Mirror’s Edge 2 and a Mass Effect game. Compare that though to
Anvil/Scimitar’s engine (famous for the Assassin’s Creed series) it gives the
game that much more. One minor drawback is games that use this engine usually
need to be built from the ground up, because of it being a multi-threading
engine allowing dynamic world creation techniques. It also influences more
middleware components that not many engines had during 2008. Some of these
components are programs like Autodesk series, HumanIK and Euphoria animation
mechanics.
Looking back at most of these engines we can see even though
they work for different devices they’re mainly console based engines. Unity
game engine is the opposite and used mainly for games that rely on Web and
Mobile platforms. Using interfaces and codes like Open GL, Open GLES, Direct X
and proprietary API support it can accommodate for a number for platforms. It’s
also dedicated to scripting language and a powerful toolset including
middleware inclusion.
Functions in an Engine
Five key subjects are important to include in a game engine
as it can be the difference between your game being a huge success, or an
amazing flop to gamers and your investments.
Rendering:
Rendering is the process of creating a model from an image
using computer aided programs such as the Autodesk Collection (Maya, 3D Max,
Mudbox ect), giving more realistic detail where performance is paramount. It’s
also the final part of the game and being one of the most important, allowing
us to see characters, environments and even art designs being the first thing a
player observes when the game is even being loaded. Yet there are a number of stages that people have
to go through in order for the visibility to be perfect, meaning that it may
limit the CPU/GPU usage which is where techniques like culling will come in.
Rendering can be integrated or dedicated to a game engine middleware component,
able of processing a number of actions like normal/texture mapping, radiosity,
shading and reflection among many others. Nowadays 3D games often require real
time rendering where the engine itself is placed into a constant update cycle
where the CPU allows the game to keep running, yet if it does not work
harmoniously with the GPU then the routine of the update cycle will be executed
stopping the game from running entirely or severely glitching.
When rendering there are two main types of illumination:
Direct illumination gives a very flat, unnatural lightning scenario which may
attempt to create a realistic and natural light using a number of sources, meaning the programmers have to
really consider where they put these lights otherwise it could look like a
mess. Sometimes the lightning may not bounce effectively off reflective
surfaces as the radiosity may not be able to work as well. It also means
lightning and shadows are diffused within the graphics.
Ray tracing though gives a realistic approach to the game
where the radiosity can work at its best, where people can actually witness
where colours meld into one another making the visual seem more rich. It even
allows for better lightning and reflective effects but one major drawback is
its heavy usage on the GPU and being costly. Another important thing to mention
is Ray Casting, which is where the light can be reflective, effectively but can never trace secondary rays
which is why people avoid putting in a house of mirrors in a game, for
rendering, the light rays will ‘break’ the GPU and be very time consuming.
Now I mentioned earlier about culling, it’s where it removes
parts of a scene that does not contribute to the final image. So during
gameplay part of the environment might fade into the background by some
mysterious fog. For example in Kingdom Hearts: Dream Drop Distance, as you
advance through worlds you’ll see the environments are simple looking shapes
until you walk up to them, then they become something like a castle or some
trees. Compare this to Legend of Zelda: Twilight Princess where a mysterious
fog won’t just appear in the game, the previous backdrops will appear/disappear
on an opacity scale which is quite common in most games. This is so the CPU and GPU don’t have to work
overtime with models that players aren’t going to see/need to see saving effort
and time. There are various culling techniques in which people use to rid unnecessary
assets in the rendering and can take place at the application, geometry or
rasterizer (provided it’s hardware assisted)
Binary Space Partitioning (BSP)
BSP is a way for subdividing a space into convex sets, the
subdivision itself will give a rise to the representation of objects within a the space by means of a tree data structure.
The tree allows 3D information about the objects in a scene considered useful
in rendering such as their ordering from back-to-front at a given location, to
be accessed rapidly as well operations with shapes in a CAD, collision
detection in models, ray tracing or other computer applications that involve
handling of complex 3D scenes.
>View Frustum
View frustum is a region of space (in the shape of a
frustum, hence name) in the game’s environment that potentially appears on the
screen. The planes that cut the frustum perpendicular to the viewing direction
are called the near plane and the far plane, anything close to the camera view
point however is clipped, the rendered when the player view (e.g the frustums
planes) come into contact with them objects.
>Back Face Culling
Back-face
culling decides whether a model/mesh is visible, testing whether the object
will appear clockwise, anti-clockwise or counter-clockwise order when visible
to the player, if however the object is
projected as counter-clockwise winding it will have to be rotated to face away
from the players perspective; not being drawn.
This
methods helps reduce the number of polygons for the program to draw, as an
example if we look at Grand Theft Auto’s city designs, there wouldn’t be any
point of modelling meshes for the sides of the buildings that face away from
the camera’s perspective within the game as they’re obstructed by the sides of
the environment that face the camera.
>Occlusion
Culling
Another similar technique to Back
Face and View Frustum is also known as Occlusion culling, which tends to skip the drawing
of models which are hidden from the viewpoint by other visible models. The
technique will only work however, with single-sided polygons whereas
double-sided polygons are rendered from both sides meaning they don’t have to be
culled by other methods such as Back Face. Occlusion culling does use
z-buffering and can be dependent on an object, only if that object isn’t
discarded from the rendering pipeline.
>Portal Culling
This technique divides
the scene with portals and manipulated camera angles. During the rendering
stage, a camera view will be in one of the rooms that’s rendered normally but
for each portal that’s visible to the player, a View Frustum is set up for the
size of the portal then the room behind it is also rendered, meaning it will be
like having two mirrors where one is underneath you and the other
perpendicularly above so that when you look in one you see the other? Hence why
these are used in indoor scenes, however they can be FoV dependant.
>Contribution Culling
Finally the last technique
is used when objects are too far away they do not contribute much to the final
image, especially if their screen projection is petite. So instead additional
features are thrown in to give the sense of illusion on distance, which could
be the reason why we see mists or fog during gameplay.
Texturing, Shaders and Anti-Aliasing
So far we’ve been through quite a bit about rendering but
there’s plenty left still to learn, for example the games and mods wouldn’t be
very detailed if it wasn’t for the fact we texture these models, for different
things like putting a certain colour on them or turning them into fire, glass,
distinguishing the difference between body parts and clothing. Textures always
need to be rendered to the power of two, so that it’s not putting the modelling
program on over-drive, will be equal and better to work with when UV mapping
and won’t look a mess when rendered, this texturing can add a lot of realism to
a game and obviously will change to suit a certain theme or style of the game.
If we compared the first Legend of Zelda to its later sequel Twilight Princess,
you’ll see the texturing has added more of a realistic and adult approach.
Legend of Zelda gameplay
Legend of Zelda: Twilight Princess gameplay
Another great thing about
texturing is that it ties in with culling, is the ability to create shadows and
fog within the game, as it gives an immersive sense of realism to the
environment by using a variety of techniques and shaders; to produce high
quality shadows. Shadows are produced
using shadow mapping which a process of where shadows are added to 3D models,
used in both pre-rendered and realtime scenes. They’re created by testing a
pixel from a light source and comparing it to a z-buffer or depth image of the
light source’s view then stored in a form of a texture. Without it that asset
could look unreal or maybe people would think there’s a constant light around
the object. One the easiest methods of shading is called Stencil Shading, which
is where an outline of, let’s say a body, is projected onto the ground as a
shadow like it would be in real life around 12pm.
Now with that in mind
shaders give the pixels themselves colour and additional attributes which adds
more for the player to see, combined with shadows and lighting effects (plus
texturing) we can see very realistic objects that will be displayed during the
game, hence why when a new generation of game or console is brought out people
always like to compare the graphics.
Anti-Aliasing is basically smoothing/ removing jagged edges
within the game. To be honest not a lot of objects or pieces take part in the
process because even it gives a high performance, it does lower the FPS and
contains an intent code. Without actually looking for it people can’t see the
difference between what is ‘AA-ed’ and what isn’t. Below is a scene taken from
Final Fantasy 14 where you can clearly see the difference of the edging with AA
involved.
Collision Detection:
This term refers to the computational problem of detecting
the intersection of two or more objects. Objects in games interact with the
player, the environment and each other and are represented by two meshes; one
being a highly rendered model to the player’s eye. However the CPU will only
recognise it as a simple shape. For example a treasure chest will appear as a
cuboid, making it easier to insert another mesh that will collide with the
other. Usually these simple meshes are collision geometery- maybe being a
bounding box, sphere or convex hull. Engines using these as a final shape for
collision detection are considered simple and can narrow the number of
collisions set on a costly mesh.
Artificial Intelligence (AI)
In video games AI is the behaviour of NPCs, however it can
be used to refer to a set of algorithms. AI can be centred on appearance of
intelligence a d amazing gameplay, being a different approach to traditional
AI; workarounds and cheats can be acceptable and in cases, the computer’s
abilities must be toned down to give human players a sense of fairness.
Constraints and Boundaries on AI
So we know AI is the behaviour of NPCs but what exactly
restrains them in a game? NPCs relate to different things, differently meaning
they’ll have dynamic responses depending on how well people have animated to
respond. Another thing is certain NPC’s might stay in one place of the level,
could accompany playable characters throughout the game or are basically
everywhere. What I’m referring to with this is those that stay in one
level/part of the game could be a member of a village? For example in Abe’s Oddysee,
Paramites (known to be enemies/ friends) only appear in Paramonia platforms and
their response to Abe depends on how many of them is around at once. If on their own they tend to help the
protagonist or moreover leave him alone fleeing to the rest of the pack, if in
a group they tend to hunt you down through the platforms until you reach higher
ground or have been killed by them or something else.
NPCs that accompany the main playable character could be
companions or have relations with the protagonist. In Okami, Issun is Ammy’s
companion and stays with her until she reaches Celestial Plains. He’s an NPC
that’s basically helps you throughout the whole game compared to another NPC
Waka (slight guardian role) who comes and goes throughout the level and
challenges you along the way, so his limelight was restricted until you were
supposed to meet him in the story whereas Issun was never really restricted in
being around you, but had to stay on Ammy’s head-unless in cutscenes.
My last idea of NPC’s being everywhere would be enemies or
‘friendly-enemies’ like guards for instance. Their paths would be set a certain
way, where if you stepped near them they surround you or follow your path
through the game. In Kingdom Hearts: Dream Drop Distance, enemies would pop
into existence as soon as you stepped foot in a certain area of the dream lands
and then disappear if you ran away from them as they couldn’t leave a set
space.
Compared to Legend of
Zelda: Twilight Princess, where in some places these foes would spot you and
continuously follow you around, grouping together until you’ve turned round and
defeated them before they get you, so basically how do creators make these
characters have set paths to follow within the game that the game engine can
understand?
Waypoints
Objects placed on waypoints are extremely limited in
functionality and don’t allow your characters dynamic adjustment, as they’re
placed on a fixed route. The polygon is placed on a navigation mesh allowing
the bot to move only in them areas, if they were to be on a bridge that’s blown
up, when they got to the end of it they couldn’t find way around the hole or
return. All that will happen is they
slight glitch then respawn back where they started or advance over to the other
side of the bridge to carry on the waypoint. This wouldn’t be very effective or
realistic but was used in early games, hence why some games you play nowadays
still do this.
Path Finding
This is another way for your NPCs to move around, since this
is a more updated version it’s therefore likely to work the opposite of
waypoints and more effectively. Path finding will allow a character to move
‘less-constrained’ within given areas so they have a more dynamic response to
things. Going back on the bridge idea, these objects would probably find a
different way to get around the hole to carry on between locations or simply
return to where it started, you might even get a certain reaction from some of
them meaning movement isn’t a problem. Still there are certain limitations to this
as it can put a constant strain on the CPU/GPU usage.
Physics
Physics are extremely important in games, by taking physic
laws from reality into the gaming world people will feel as though they game
itself is better. We need physics in games for everything that needs to move,
move which is what animation is there for and even that’s limited by physics
laws. We wouldn’t allow characters to simply walk through heavy wind without
being slowed down or blown away, or if they have a high jump it can only be used
for certain ledges not every tall ledge. In the Spyro the Dragon series, Spyro
could only fly a certain distance as a young dragon and do a quick hover to get
across ledges in order to get treasures, eggs, orbs ect As he was only a young
dragon they wouldn’t have developed the muscles in their wingspan to carry them
for long distances which limits the players to certain actions but challenges
them to get to certain places by finding another way or completing side-quests
adding more of a natural effect.
Two well-known game engines called HavoK and PhysX are
basically physics engines designed for games allowing real time collision and
dynamics of rigid bodies in 3D. HavoK itself provides different types of
dynamic constraints between rigid bodies by using what’s known to be a
dynamical simulation, creating more realistic virtual worlds in games. Their
sub-company known as Havok Animation provides the user with efficient playback
and compression of animations for characters in the games, featuring inverse kinematics.
Games that use this engine are: Darksiders 2, Ni No Kuni and Super Smash
Brothers Brawl.
Now PhysX is classed a proprietary real-time physics engine
middleware SDK. Games that support hardware acceleration by PhysX itself can be
sped up by either PhysX PPU or a CUDA-enabled GPU, allowing physics
calculations from the CPU to be off-loaded, whilst the CPU can perform other
tasks instead-giving a smoother gaming experience and space for additional
visual effects. Usually middleware physics engines will let game developers
avoid writing down their own code, to see to complex physics interactions that
appear in modern games, hence why PhysX is
vastly popular among game engines and is available for Microsoft Windows,
Mac OS X, Linux, PlayStation 3, Xbox 360 and the Wii, Games that have used this
engine are: Borderlands 2, Mirror’s Edge and Alice: Madness Returns.
Sound
Game sounds are extremely important to the player as it
helps make the game seem more genuine and can give a set of codifiers to help
in the game. For instance, people who have played Zelda always know when
they’ve opened a chest or found something useful as the tune goes:
‘den-nah-nah-nah’, compared to when they’ve found a rupee in a chest or when an
enemy is about to attack, as instant alarming music will immediately take over
the original soundtrack pieces set in each part of Hyrule until it fades away
again.
It can also give characters a voice which is why
voice-acting is important to games like Personna, Final Fantasy, Professor
Layton ect as their games contain cinematic/anime cut scenes triggered
throughout the game. Sound can define our actions and the games reactions so we
don’t get confused between rules.
Networking
Usually we like to keep updated with the world and tell
everybody we know what we are doing throughout most of the day, also hearing
what our friends have done through social networking sites. Since most consoles
now allow us to connect to the internet and even have famous networking sites
like Facebook, Twitter, Bebo integrated into the system we can still play games
and keep updated. Networking can handle game interaction over the internet
easily nowadays which is what MMO and MMORPG games like World of Warcraft,
Howrse and Pottermore rely on. It means players across the world can control
their personal avatar to interact with others, so the game doesn’t have as many
NPCs as it normally would in a console game. It also means we are susceptible
to recent upgrades that give us DLC, help our consoles/ games and receive messages
from across the world.
