Computer Graphics Coursework Cookbook original from Anthony Jones modified Dan Cornford (Oct 2010)

Computer GraphicsCoursework Cookbook

original from Anthony Jonesmodified

Dan Cornford (Oct 2010)

Introduction• Me– Dan Cornford– Used to teach this before I got sacked ...

• You– Computer graphics students– Attending labs?

• This lecture– Aims to help you with your coursework– Available online...

2

Lecture Outline• The specification

• Approaching the problem– Simplification– Paper designs as stepping stones– Scene graphs– Objects– Animations– Lights– Cameras

• Lecture outcomes• Where to get further help

3

The Specification• It’s a checklist

– Covering everything you’ll see in the labs

• Try to tick off as much as you can– Some items are easier or

harder than others– Some items are related

• The checklist is flexible– Remi will give you marks

where you deserve them!

A total of 100 marks is available and will be allocated along the following lines:

• Basic 3D OpenGL program which renders correctly [10]

• A basic animation (e.g. movement) of a simple object [5] with basic user interaction [5]

• A self created, well defined 3D object with correct normals [10]

• Sensible use of lighting, materials and textures [15]

• Advanced animation (not just static objects moving, but components that move relative to each other) [10]

• The clarity of the code [5], and good documentation of the program [5]

• A clear introductory description of the program [5], and a correct scene graph [5]

• Innovation and novelty in the animation (your ideas - can't tell you this bit!) [25]










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5

























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7

The Specification

• Topic changes every year– What is the topic this year?

• Lecture example:– Topic: “A sporting event”– Idea: England won the

world cup in 1966

• How do we turn this idea into code?

8

Approaching The Problem:Mind the Gap!

protected void renderScene() { // draw the ground plane GL11.glPushMatrix(); { // position, scale and draw the ground plane GL11.glTranslatef(0.0f,-2.15f,-10.0f); GL11.glScaled(10.0f, 1.0f, 10.0f); drawUnitPlane(); } GL11.glPopMatrix();

// position, rotate and draw the person GL11.glTranslatef(0.0f,personOffsetY,-10.0f); GL11.glRotatef(personSpinY, 0.0f, 1.0f, 0.0f); person.draw(); }

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The Wrong Approach

10

The Right Approach

• Methodical, incremental development based on a careful design

• Treat the specification as a checklist• Customize the coursework template

11

The Right Approach

• Methodical, incremental development based on a careful design

• Treat the specification as a checklist• Customize the coursework template

• Keep It Short & Simple! (KISS)“Everything should be made as simple as possible, but no simpler.” (Albert Einstein)

12

The Right Approach

protected void renderScene() { // draw the ground plane GL11.glPushMatrix(); { // position, scale and draw the ground

plane GL11.glTranslatef(0.0f,-2.15f,-10.0f); GL11.glScaled(10.0f, 1.0f, 10.0f); drawUnitPlane(); } GL11.glPopMatrix();

// position, rotate and draw the person GL11.glTranslatef(0.0f,personOffsetY,-10.0f); GL11.glRotatef(personSpinY, 0.0f, 1.0f, 0.0f); person.draw(); }

Objects

Animations

Lights

Cameras

13

Simplify Your 3D Scene

• Remember to KISS!• Ideas Paper design– Objects– Animations– Lights– Cameras

• Paper Design Code

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15

Paper Design

• Pencil and paper– Remember to KISS!– Start in 2D and move to 3D later– Use different colours

• Understand your scene as:– Scene graph– Objects– Animations

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Scene Graphs

• Nodes• Arcs Sun

Earth

Moon

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Scene Graphs

• Nodes– Scene objects– Based about a

centroid• Typically a central

point• Defines the object’s

position• “Object handle”

Sun

Earth

Moon

18

Scene Graphs

• Arcs– Connect one node

centroid to another– Create a node

hierarchy• Node ownership• Node dependency

Sun

Earth

Moon

19

Scene Graphs

• Body• Head• Arms:– Shoulder– Upper Arm– Elbow– Lower Arm

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Scene Graphs

• Body• Head• Arms• Waist• Legs:– Hip– Upper Leg– Knee– Lower Leg– Foot

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•Each leg:•Hip•Upper leg•Knee•Lower leg•Foot

Body

Head

Waist

World Origin

•Each arm:●Shoulder●Upper arm●Elbow●Lower arm

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Exercise 1: Draw The Scene Graph

Upper arm

Elbow Lower arm Upper claw

Lower clawWrist

Shoulder

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Exercise 1: Solution

Upper arm

Elbow

Lower arm

Upper claw

Lower claw

Wrist

World Origin

Shoulder

24

Scene Graphs Code

• Start at the world origin

• Traverse your scene graph• Move from one object to

another• Move along the arcs• Move down and right only

Sun

Earth

Moon

Mars

Phobos

Deimos

Scene Origin

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Scene Graphs Code

• Each time you move along an arc, you need a matrix transform• Typically a translation

and/or a rotation• Sometimes the identity

matrix

Sun

Earth

Moon

Mars

Phobos

Deimos

Scene Origin

26

Scene Graphs Code

• When you reach an object, draw it• Using your own objects• Using GLUT quadrics

Sun

Earth

Moon

Mars

Phobos

Deimos

Scene Origin

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Scene Graphs Code

• Traverse your scene graph• Move from one object to

another• Move along the arcs• Move down and right only

• What happens when you reach the Moon?• You can’t go down and

right!

Sun

Earth

Moon

Mars

Phobos

Deimos

Scene Origin

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Scene Graphs Code

• Use the matrix stack to jump between nodes• PushMatrix saves your

current position• PopMatrix restores the

last saved position

• So...• Push at the Sun• Traverse to the Moon• Pop back to the Sun

Sun

Earth

Moon

Mars

Phobos

Deimos

Scene Origin

(PUSH)

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Scene Graphs Code

• Once you’re back at the Sun...• Traverse to Mars• Push Mars• Traverse to Phobos• Pop back to Mars• Traverse to Deimos

Sun

Earth

Moon

Mars

Phobos

Deimos

Scene Origin

(PUSH)

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Scene Graphs Code

• Simple rule:

For each child in the current object’s children

{PushMatrix();

Transform to childDraw child

PopMatrix();}

Sun

Earth

Moon

Mars

Phobos

Deimos

Scene Origin

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Paper Design



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Objects

• Centroids– “Object handles”

• Unit sizes– Unit cube– Unit quad

• GLU Quadrics• Your own objects• Materials and textures

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Objects




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1 unit

Objects




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GLU Quadrics• “Automatic” objects• Spheres, cylinders and disks• Much of the work is done for you– Vertices calculated for you– Faces defined for you– Surface normals calculated for you

• Provide appropriate parameters– Commonly defined by radius, slices and stacks (disks

have loops instead of stacks)• Check the documentation

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Objects




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Defining Your Own Objects

• Position centroid– at {0.0, 0.0, 0.0}

1 unit

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• Position centroid• Define vertices

– A {-0.5,-0.5,+0.5}– B {-0.5,+0.5,+0.5}– C {+0.5,+0.5,+0.5}– D {+0.5,-0.5,+0.5}

A D

B C

1 unit

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• Position centroid• Define vertices

– A {-0.5,-0.5,+0.5}– B {-0.5,+0.5,+0.5}– C {+0.5,+0.5,+0.5}– D {+0.5,-0.5,+0.5}– E {-0.5,-0.5,-0.5}– F {-0.5,+0.5,-0.5}– G {+0.5,+0.5,-0.5}– H {+0.5,-0.5,-0.5}

A D

B C

E

F G

H

1 unit

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Defining Your Own Objects• Position centroid• Define vertices• Define faces

– Front {C, B, A, D}– Left {B, F, E, A}– Back {F, G, H, E}– Right {G, C, D, H}– Top {C, G, F, B}– Bottom {D, A, E, H} A D

B C

E

F G

H

1 unit

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B C

E

F G

H

1 unit

42



B C

E

F G

H

1 unit

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B C

E

F G

H

1 unit

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B C

E

F G

H

1 unit

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B C

E

F G

H

1 unit

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Defining Your Own Objects• Position centroid• Define vertices• Define faces• Normals

– Java Normal class– 3 Vertex parameters

– Same order as when defining faces

– Should be clear from the lab code

C

E

1 unit

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Exercise 2: Define The Pyramid• Position centroid {0.0,0.0,0.0}• Define vertices

– A {-0.5,-h/2,+0.5}– B {?,?,?} – C {?,?,?} – D {?,?,?}– E {?,?,?}

• Define faces– Front {A, B, E}– Left {?,?,?}– Back {?,?,?}– Right {?,?,?}– Bottom {?,?,?,?}

1 unit

h units

A B

C D

E

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Exercise 2: Solution• Position centroid {0.0,0.0,0.0}• Define vertices

– A {-0.5,-h/2,+0.5}– B {+0.5,-h/2,+0.5} – C {-0.5,-h/2,-0.5} – D {+0.5,-h/2,-0.5}– E {0.0,+h/2, 0.0}

• Define faces– Front {A, B, E}– Left {C, A, E}– Back {D, C, E}– Right {B, D, E}– Bottom {C, D, B, A}

1 unit

h units

A B

C D

E

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Objects




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Materials And Textures

• Did you remember to KISS?• Use materials and not colours– More marks for you!– Make sure you’ve removed any glColor calls

• Use Nate Robins’ online tutorial programs– Interactive– Choose material properties for your objects

• Only texture square faces– Ask in the labs for help with other shapes

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Paper Design



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Animations

• 2 types of animation1. User controlled

animation2. Scripted animation

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All Animations• 5 simple steps:

1. Identify animated transforms

2. Declare variables for angles and offsets

3. Initialize your variables when they are declared

4. Update your variables in your updateScene method

5. Use your variables in your drawing methods

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User Controlled Animations

• Adding user interaction to your animations– Don't update your

variables in your updateScene method

– Modify them in your checkSceneInput method instead

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Scripted Animations• 5 simple steps:

1. Identify animated transforms

2. Declare variables for angles and offsets

3. Initialize your variables when they are declared

4. Update your variables in your updateScene method

5. Use your variables in your drawing methods

• Use animation scripts in your updateScene method to change your scene at runtime according to a set of predefined rules

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Scripted Animations

• Make the pendulum swing

Frame57

Scripted Animations

• Make the pendulum swing– 60 degree swing

Frame58

Scripted Animations


Frame

frame = 0swing = 0.0

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Scripted Animations


Frame

frame = 30swing = -30.0

30

60

Scripted Animations


Frame

frame = 90swing = +30.0

30 60

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Scripted Animations


Frame


30 60 30

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Scripted Animations


Frame


30 60 30

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Pendulum Code // increment the frame counter ++frame;

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if (frame < 30) // During the first 30 frames, { swing = swing - 1.0; // swing the pendulum to the left }

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if (frame < 30) // During the first 30 frames, { swing = swing - 1.0; // swing the pendulum to the left } else if (frame < 90) // During the next 60 frames, { swing = swing + 1.0; // swing the pendulum to the right }

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if (frame < 30) // During the first 30 frames, { swing = swing - 1.0; // swing the pendulum to the left } else if (frame < 90) // During the next 60 frames, { swing = swing + 1.0; // swing the pendulum to the right } else if (frame < 120) // During the next 30 frames, { swing = swing - 1.0; // swing the pendulum back to 0 }

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if (frame < 30) // During the first 30 frames, { swing = swing - 1.0; // swing the pendulum to the left } else if (frame < 90) // During the next 60 frames, { swing = swing + 1.0; // swing the pendulum to the right } else if (frame < 120) // During the next 30 frames, { swing = swing - 1.0; // swing the pendulum back to 0 } else { frame = 0; // Reset the animation }

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69

Lights

• Global properties• Per-light properties

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Lights// global ambient light levelfloat globalAmbient[] = {0.2f, 0.2f, 0.2f, 1.0f};// set the global ambient lightingglLightModel(GL_LIGHT_MODEL_AMBIENT, globalAmbient);

// the first light for the scene is soft blue...float diffuse0[] = { 0.2f, 0.2f, 0.4f, 1.0f};// ...with a very dim ambient contribution...float ambient0[] = { 0.05f, 0.05f, 0.05f, 1.0f};// ...and is positioned above the viewpointfloat position0[] = { 0.0f, 10.0f, 0.0f, 1.0f};

// supply OpenGL with the properties for the first lightglLight(GL_LIGHT0, GL_AMBIENT, ambient0);glLight(GL_LIGHT0, GL_DIFFUSE, diffuse0);glLight(GL_LIGHT0, GL_POSITION, position0);// enable the first lightglEnable(GL_LIGHT0);

// enable lighting calculationsglEnable(GL_LIGHTING); 71

Lights

• Global properties• Per-light properties– 8 lights in total– Named GL_LIGHT0 to GL_LIGHT7– Describe, enable and disable each one separately

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Lights// global ambient light levelfloat globalAmbient[] = {0.2f, 0.2f, 0.2f, 1.0f};// set the global ambient lightingglLightModel(GL_LIGHT_MODEL_AMBIENT, globalAmbient);

// the first light for the scene is soft blue...float diffuse0[] = { 0.2f, 0.2f, 0.4f, 1.0f};// ...with a very dim ambient contribution...float ambient0[] = { 0.05f, 0.05f, 0.05f, 1.0f};// ...and is positioned above the viewpointfloat position0[] = { 0.0f, 10.0f, 0.0f, 1.0f};

// supply OpenGL with the properties for the first lightglLight(GL_LIGHT0, GL_AMBIENT, ambient0);glLight(GL_LIGHT0, GL_DIFFUSE, diffuse0);glLight(GL_LIGHT0, GL_POSITION, position0);// enable the first lightglEnable(GL_LIGHT0);

// enable lighting calculationsglEnable(GL_LIGHTING); 73

Cameras

• gluLookAt(x,y,z, x,y,z, x,y,z)– Camera position (x,y,z)– Target position (x,y,z)– Up vector (x,y,z)

74

Cameras

• gluLookAt– Camera position (x,y,z)– Target position (x,y,z)– Up vector (x,y,z)

75

Cameras

• gluLookAt– Camera position (x,y,z)– Target position (x,y,z)– Up vector (x,y,z)

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Cameras

• gluLookAt– Camera position (x,y,z)– Target position (x,y,z)– Up vector (x,y,z)• (0.0,1.0,0.0) in most cases

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Cameras

• gluLookAt– Camera position (x,y,z)– Target position (x,y,z)– Up vector (x,y,z)• (1.0,0.0,0.0) or• (0.0,0.0,1.0) when looking down

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Lecture Outcomes: A Better Approach

1. Design a simple scene– Think about how you can satisfy the coursework

specification; treat it as a checklist2. Understand your scene with a paper design– Scene graphs– Objects– Animations– Lights– Cameras

3. Translate your paper design to OpenGL code– A simplified process using scene graphs

79

Where To Get Help• Did you remember to KISS?• Return to pencil and paper• Labs

– Lab notes– Lab examples– Lab demonstrators

• Internet and others– But be careful to avoid

collusion– It’s a bit obvious…

• Remi ...

80

Lecture Summary• The specification

• Approaching the problem– Simplification– Paper designs as stepping stones– Scene graphs– Objects– Animations– Lights– Cameras

• Lecture outcomes• Where to get further help

81

Thanks for listening

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Computer Graphics Coursework Cookbook original from Anthony Jones modified Dan Cornford (Oct 2010)

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Transcript of Computer Graphics Coursework Cookbook original from Anthony Jones modified Dan Cornford (Oct 2010)