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COM 366

Interactive Computer Graphics

Topic 1 : Introduction

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Y

X

(2,2)

N1

N2

N3

N4

(2,-2)(-2,-2)

(-2,2)

A simple data structure

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plot(X,Y)

Drawing a line in Matlab

(-1,-2)

(3,4)

X = [ -1 3] Y = [ -2 4]

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function LineDemo;

%To draw a single line

%First of all define the two node vectors

X = [-1 3];

Y = [-2 4];

%Draw the line

plot(X,Y)

%Set the limits to the axes and ensure they %are of equal dimension

axis([-5,5,-5,5]);

axis square;

Drawing a line with MATLAB

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The line drawn

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plot(X,Y,'Color','red','LineWidth',2)

Changing the appearance of the line

X Y

-2 -2

-2 2

2 2

2 -2

-2 -2

Column vectors for drawing the square

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Combining the X and Y arrays

Node = [-2 -2; -2 2; 2 2; 2 -2;-2 -2];

(-2,-2) (-2,2)

(-2,2) (2,2)

(2,2) (2,-2)

(2,-2) (-2,-2)

Y

X

(2,-2)(-2,-2)

(2,2)

N1

N2N3

N4

(-2,2)-2, -2

-2, -2

2, 2

2, -2

-2, -2

Column 1

Row 3

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A useful Matlab convention

Node = [-2 -2; -2 2; 2 2; 2 -2;-2 -2];

Node(:,1) Means take ALL rows from column 1 of array node

Node(3,:) Means take ALL columns from row 3 of array node

Node(1..3,1) Means take rows 1 to 3 from column 1 of array node

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function Drawsquare;%To draw a square using nodes%First of all define the nodesNode = [-2 -2; -2 2; 2 2; 2 -2;-2 -2];%Draw the squareplot(Node(:,1),Node(:,2))axis([-5,5,-5,5]);axis square;

Drawing the square

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function Drawsquare2;%To draw a square using patch%First of all define the nodesNode = [-2 -2; -2 2; 2 2; 2 -2];%Draw the squarepatch(Node(:,1),Node(:,2),'red')axis([-5,5,-5,5]);axis square;

fill(Node(:,1),Node(:,2),C)

Alternative ways of drawing the square

Using ‘patch’ Using ‘fill’

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patch(x-coordinates,y-coordinates,[z-coordinates],colordata)

Drawing in three dimensions

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The viewing pipeline

Data ModelApplication

ProgramSoftware

PrimitivesHardware

Primitives &Device control

Display

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Primitive Function

Plot(X,Y,props) Draw a graph of the object defined by the X,Y vectors using a particular set of properties – line colour, thickness etc.

Subplot(m,n,p) Allows you to display m rows and n cols of sub plots in a single window. p is the current plot to be drawn.

Fill(X,Y,C) Fill a polygon defined by X and Y with colour C

Patch(X,Y,Z,C) Creates a patch in 3D defined by the colour C. C can in fact be quite sophisticated allowing shading across the patch

Camera Not really a primitive as such but gives access to a huge range of properties to configure the viewing of a 3D object

Light(props) Creates all the properties of a light source to view a scene.

Camlookat Position the camera to view an object or group of objects

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Degrees and radians

Most computer languages (including Matlab) like to use angles in

Radians in their trigonometric functions like sine and cosine

We normally like to think in degrees. Fortunately the conversion is

easy if you remember that : Radians is equivalent to 180o

So for example 45o is 45 * pi/180 radians

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function Circle(R);%Draws a circle centred on the origin of radius Rt = 0:pi/36:2*pi;x = R*sin(t);y = R*cos(t);fill(x,y,'w')axis square

Adding a circle primitive

pi is the Matlab convention

for = 3.1416…..

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