Ics2311 l02 Graphics fundamentals

Bridgekloud
Graphics Fundamentals
Lesson 2
Bridgekloud: https://www.bridgekloud.com Unit: Computer Graphics ICS2311

FundamentalsOutline
 Historical perspective
 Model of a Computer - Memory & Graphics
 Devices
 Raster Model & Bitmaps
 Coordinates
 Drawing Spaces
 Colors
 Graphics Libraries

BriefHistory
 Teletypes(pre 1950s), DisplayTubes(postWW2),
CRTs(last half of 20th century), Flat Panels
(modern era)
 Size and Quality (eg resolution) driven by
economics (eg 640x320…1024x768…)
 Vector (circaWW2) & Raster/Bitmap models
 Devices & Human / Machine Interaction
 Memory and Processing Speed limitations

ComputerMemoryModel
 Main Memory
 Graphics memory
 Used to be limited to separate amount on eg graphics
card
 Modern idea is to partition main memory dynamically
(ie by software instruction)
 Modern idea is to map memory to the display
 Independent of display hardware type

ComputerMemoryModel cont…..
 CPU + Cache memory + Main memory
 Cache memory is fast but expensive so (still
often) only have small amount eg 512kBytes
available
 Main memory relatively plentiful (eg GBytes)
but slow

Memory&Graphics
Idea is that we can write programs that interact with
the graphical display device simply by writing to a
predetermined area of the computer’s memory
 Known as Bitmap graphics
 The bits are mapped to the pixels
 Flexible, portable software
 Independent of Hardware & Operating System

GraphicalDevices
Devices eg mouse, stereo glasses, tracker ball, light pen, touch
screen, 3d-wand, “rat”, sensor gloves, head tracker, iris tracker,…
Even Mouse varies in form factor and number of buttons
 Main Memory
 Graphics memory
 Used to be limited to separate amount on eg graphics
card
 Modern idea is to partition main memory dynamically (ie
by software instruction)
 Modern idea is to map memory to the display
 Independent of display hardware type

GraphicalDevices
 Mouse - most well known device
 Buttons, and scan movements
 Jargon ideas that have become common:
 Drag
 Click
 Double-Click
 Left -Click
 Main idea is to let you specify a location in a space eg x,y (or
x,y,z) coordinates

RasterModel-Pixels
Pixel or sometimes “pel” Picture Element
Each pixel is a sample that can be rendered as a dot or
rectangle on the screen
Often try to design them as squares but not always
 Might be implemented as small area of
phosphor on a monochrome monitor
 Or three areas of eg red, green and blue
phosphors for colour
 Or simple a transistor logic gate assembly on
a flat panel display

CoordinateSystems
 Pixel Coordinate System - rows and columns
 Rectilinear
 Usually for graphics, we start at top left corner and work our
way across and down
 Same as raster orientation
 Array[row][column]
 Row major used in C and C+ ( last index moves
fastest in memory)
 Not all languages do it this way - eg Fortran
uses column major (first index moves fastest)

CartesianCoordinates
Often we use the Cartesian
coordinate convention ie x,y
coordinates (or x,y,z in 3D) and
map this to our display
Usually column corresponds to x,
and -row corresponds to y
 This works if we know the
max min values.
 Common values are eg
640 columns x 320 rows
 Or 1024x768 or better
 Aspect ratio is the ratio of
these eg 4:3 - Chosen to
suit the common display
devices egTV screens or
monitors
x
y

DrawingSpaceorCanvas
Coordinate Systems
Drawing Primitives
Library of utilities
 eg drawDot( int x, int y);
 Or drawLine( x1, y1, x2, y2 );
Usually we have “Primitive”
Models for coordinate spaces and
colours
 We do not want to write
our application programs
worrying about pixel
resolutions
 We may have libraries
that allow us to do so,
but often they will
support more general
coordinates
 Eg real space
“normalised”
coordinates [0.0,1.0]

ColoursinBrief
Red Green Blue is not the Only
colour model although still most
common
We specify separate RGB
values for each pixel
They map to intensities
All colours can be expressed as
combination of these
Sometimes also an “alpha” or
transparency value
 These will conveniently pack
into a computer word of 4
bytes, one byte for each
entity
 1 Byte gives us 256 values -
hence numbers of colours
 Need not use this
resolution
 Can also use Look-up tables
to save memory

GraphicsLibrariesandpackages
What is a graphics system?
A package or Library that links to a Language or
environment and lets us write programs that are
independent of the graphics
Java Development Kit and Java 2D and Java 3D
libraries
GL and OpenGL (Graphics Library),VOGL
X11, DirectX, PHIGS,… and lots of others

JavaGraphicsProgramOutline
 A short example- MyProg01 draws a black
rectangle inside a white rectangle
 See the course web pages for these codes
 Use a text editor or your favourite text tool
(eg emacs or vi or notepad) to create
MyProg01.java
 Compile it using javac MyProg01.java
 Run using java Myprog01

Java GraphicsCodeFragment
// g2 is the Graphics2D object supplied by the system…
g2.setBackground( Color.white ); // set background colour
g2.clearRect( 0, 0, getWidth(), getHeight() ); // clear an area
g2.setColor( Color.black ); // set the drawing colour
g2.fillRect( 10, 10, 20, 20 ); // fill in a rectangle of that colour
g2.drawRect( 0, 0, getWidth()-1, getHeight()-1 ); // draw a border around everything
 More on how this works next lecture and at the
tutorials…

WhatMyProg01OutputLooksLike
Black rectangle inside a white area…

Summary
Graphics has a varied history
Very technology driven
Good advances in recent years with
adequate memory and processing
power
Primitives and library layers approach
is very common
 Note devices and
memory model
 Colour models and
drawing spaces are
important ideas for our
programs
 We will use the Java
Development Kit
graphics libraries and
primitives

Ics2311 l02 Graphics fundamentals

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