D. Hunter Hale Lecture 13

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6 Νοε 2013 (πριν από 4 χρόνια και 8 μήνες)

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D. Hunter Hale

Lecture 13


Term Next Tuesday

Review Sheet by Tomorrow at 11:59

Homework 3


Remember the expected unforeseen
circumstances shifting when I collect them

Graduate Student Fun

Each graduate student will do a 15 min
presentation based on state of the art techniques
in game engines

Midterm Course Status

Official Course Goals

Graphics Rendering Pipeline (transformations, lighting
,shading); 2D/3D Texture Mapping; Image Based
Rendering; Spatial Data Structures and Acceleration
Algorithms; Level of Detail; Collision Detection, Culling
and Intersection Methods; Vertex/Pixel
; Pipeline
Optimization; Rendering Hardware.

Additional Course Material

Game Engine Architecture, Advanced

Programming, HUD & HCI design, Data logging,
Advanced Lighting and Shadows, Non
Photo Realistic
and Stylistic Rendering, Timing and Render Loop
, Camera Management

Official Course Goals

Graphics Rendering Pipeline (transformations, lighting
,shading); 2D/3D Texture Mapping
Image Based
Spatial Data Structures and Acceleration
Level of Detail
; Collision Detection,
and Intersection Methods
; Rendering Hardware.

Additional Course Material

Game Engine Architecture
, Advanced

HUD & HCI design
Data logging
Advanced Lighting and Shadows, Non
Photo Realistic
and Stylistic Rendering,
Timing and Render Loop
, Camera Management

Rendering Spectrum

Normally we render using Triangles
however other techniques exist

There are many ways to use pre
textures and images to fake geometry

View Effects

Suppose that you know the view position for
every scene in your game

Using this information:

Render you world in advance and high quality

Display this texture at runtime


Render a depth map along with your world

Render dynamic scene objects by comparing with
this depth map and rendering behind/in front of
the background image

Light Field Rendering

Light Field Rendering is the science of
capturing a single object from many

Can be used in engines to fake small
complex objects

Find the two closest viewpoints to the current
camera position on the object and interpolate

Why only small objects complex objects?

Sprites and Layers

One of the oldest techniques in

A sprite is a texture image that is drawn
directly to the screen (i.e., a mouse

Layers of sprites can be built up to
represent complex looking scenes using
just textures

Think image layers in


Allows for the placement of arbitrary
textures into space

Generally constructed from three

Up Vector

Surface Normal

Anchor Location

Using these three things we

we build translation and

rotation matrix to place the

billboard . The rotation matrix

is constant for all billboards

Aligned Billboard

Similar to sprites

the billboard is always

to the screen

up vector is constant

Generate a surface normal by taking the
negation of the view planes normal

Up vector is taken directly from the camera

Generally used to display text or other fixed
images in the game world hence the name


Unlike Screen
Aligned these billboards
display objects present in the game

Therefore use the worlds up vector,
while still using the cameras view plane
to find the normal

Problems for World

Using the same normal

can result in distortion

(due to

Instead calculate each

billboards normal

direction separately

using the center of

the billboard

and the viewpoint

Billboards for Clouds/Weather

In general billboards work well to show
atmospheric effects such as clouds or
billowing dust

Problems with Billboard Clouds

One common problem with billboard cloud
effects occur when solid objects intersect


doesn’t perform proper clipping

Instead fade

out the clouds

when they

are near


Axial Billboards

Instead of directly facing the view these
billboards are attached to a fixed world
space axis

The billboard

faces the view

as best they can

along this axis

Commonly used

for cylindrical

objects and

death rays

Particle Systems

Particle systems represent a set of small
objects that independently move according to
some algorithm

Each object is represented as a single textured
quad or a colored point

Common applications for particles are fire,
smoke, explosions, water flows, trees.

Modern Particle Systems

Historically particle systems were executed
exclusively on the

Now modern particle systems can exist

be maintained entirely

on the GPU. Particles

are birthed using the


animated on the

, and

drawn with a fragment


Billboard Clouds

Not to be confused with using billboards
for clouds a Billboard Cloud is
something entirely different

In this technique instead of using one
image to represent an object you can
procedurally reduce an object down to
dozens of images

This allows for a dramatic reduction in
the number of polygons to be rendered
but still yields objects that look “real”

Billboard Cloud Example

Polygon Tree:

20,610 triangles

Polygon Tree


Billboard Cloud Tree

Billboard Cloud


156 triangles

Displacement Techniques

These techniques allow a sprite image
to store depth information for each pixel
(depth sprites or

This allows each

pixel of a sprite

to adjust its



Image Post Processing

Effectively the modern pixel

present in GPU are extremely effective
image processing units

By rendering a 3D scene twice (one to a
texture and then again a full screen
image) any number image processing
algorithm can be applied to it.

Color Correction/Tone Mapping

Normally use 2 or more sets of textures to
represent different lighting tones or modes in a

Instead apply a transform lookup function

This function

is generally a

1D texture

enter a color

value pull the

resulting color

High Dynamic Range Imaging

The intensity of light in a real scene can vary
greatly (1000
10000X difference in luminance)

Unfortunately light data is generally stored as
4 bytes. This limits the different to in lighting
in a scene to 0

Solution: Render the scene once for each
group of radically different illuminated objects
then composite the final image together

Lens Flare and Bloom

Lens Flares are caused by imperfections
in the camera lens and the internal
geometry of the camera

These rarely appear in photograph since
the introduction of better cameras

However, they are almost expected in

games and easy to create

Lens Flare Implementation

Draw colored billboards over the areas
expected to have a lens flare, the color
of these billboards determines the flare

Blend these boxes with a series of flare
mask textures

Depth of Field

The in photography there is a concept of
focal depth where objects outside this
depth appear blurry

This can be used to highlight or draw
attention to certain areas of the screen

This can be coded

by using the depth

buffer to determine

if a pixel should be

blurred when it is


Motion Blur

Initially caused by the sampling rates of
camera. The camera shutter is open for
a finite amount of time and the objects it
is viewing are moving during that time

Conversely when rendering a scene the
“camera” we use is instantly open and
closed. We are effectively instantly
“sampling” our scene

Two Motion Blur Implementations

Accumulate multiple frames
and blend between them to
produce a ghost movement

Encode the direction of
movement into a render
buffer and blur moving
objects based on their

Advanced Fog

As we discussed previously fog is just a
simple matter of comparing the depth
value of a pixel to a fog equation

But this produces fog that is always flat to view and can cause artifacts if the user

rotates their view.

Volume Rendering

In addition to 2D images textures can store
3D spatial data. Effectively this lets a texture
represent some volume of space (

This data can be accessed by casting rays
through the

data on the pixel

). Using

this environmental or

physicals data this encoded

into a

can be

presented in real time.

(e.g., fire, smoke, liquids)

Fur and Hair

Using modern graphics hardware (DirectX 11,
OpenGL 4) it is possible to physically simulate
hair and fur at runtime.

The color length and angle of the fur is
encoded onto a surface. Then the geometry



this information

and adds lines

to the world that

represent this

new geometry