CS380 LAB IVOpenGL

Jonghyeob Lee

Reference1. [OpenGL course slides by Rasmus Stenholt]

Reference2. [http://nehe.gamedev.net/]

Goal

Introduce OpenGL programming Help you do CS380 homework by yourself

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Notice

Use Noah board for your questions (http://noah.kaist.ac.kr/course/CS380)

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Outline

Lighting and Materials Texture Mapping

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Lighting and Materials

Why is this important? Geometry is only one third of rendering Lights and materials make up the other two Unlit objects tend to look dull and artificial

In OpenGL, lights and materials are connected Light interacts with materials Materials must be assigned to geometry to benefit

from lighting

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Lighting Principles

The result of lighting depends on various factors Material composition of object Light colour and position Global lighting parameters

ambient light two sided lighting

Lighting can be done in both RGBA and indexed color mode

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OpenGL Lighting

Lighting is computed per-vertex The lighting model is called Phong

shading Lighting properties

DiffuseSpecularAmbient

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Lighting

Normals define how a surface reflects light glNormal3f( x, y, z )

Normals can be defined per-vertex Just like colours

The current normal is used to compute lighting contributions The angles between the normal and light directions are used Use unit normals for proper lighting

Some transformations affect a normal’s length glEnable( GL_NORMALIZE )

or glEnable( GL_RESCALE_NORMAL )

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Light Properties

The command for setting lighting properties glLightfv(light, property, value); light specifies which light

Multiple lights, starting with GL_LIGHT0glGetIntegerv( GL_MAX_LIGHTS, &n );

The maximum number of lights is usually 8 Properties

colors position and type attenuation

Light color properties GL_AMBIENT GL_DIFFUSE GL_SPECULAR

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Types of Lights

OpenGL supports two types of lightsLocal (Point) light sources Infinite (Directional) light sources

Type of light controlled by w coordinate

Usually w=1 for a point light

wzw

ywxw

zyxw

at positioned Light Local

along directed LightInfinite

0

0

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Turning on the Lights

First you must tell OpenGL that lighting should be usedglEnable( GL_LIGHTING );

Then each light can be individually turned on/offglEnable( GL_LIGHTn );

Load a solid teapot

Tutorials

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void display() {glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);glMatrixMode(GL_MODELVIEW);glutSolidTeapot(0.5);glFlush();

}

Tutorials

Add a light on previous scene

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void display() {glEnable(GL_LIGHTING);glEnable(GL_LIGHT0);float light_pos[] = {-2, 2, 2, 1};float light_Ka[] = {0, 0, 0, 1};float light_Kd[] = {1, 1, 1, 1};float light_Ks[] = {1, 1, 1, 1};glLightfv(GL_LIGHT0, GL_POSITION, light_pos);glLightfv(GL_LIGHT0, GL_AMBIENT, light_Ka);glLightfv(GL_LIGHT0, GL_DIFFUSE, light_Kd);glLightfv(GL_LIGHT0, GL_SPECULAR, light_Ks);…

}

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Material Properties

Define the surface properties of a primitive glMaterialfv( face, property, value );

Separate materials for front and back

GL_DIFFUSE Base color

GL_SPECULAR Highlight Color

GL_AMBIENT Low-light Color

GL_EMISSION Glow Color

GL_SHININESS Surface Smoothness

Tutorials Add a materials on front

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void display() {float material_Ka[] = {0.11, 0.06, 0.11, 1.00};float material_Kd[] = {0.43, 0.47, 0.54, 1.00};float material_Ks[] = {0.33, 0.33, 0.52, 1.00};float material_Ke[] = {0.00, 0.00, 0.00, 0.00};float material_Se[] = {10};glMaterialfv(GL_FRONT, GL_AMBIENT, material_Ka);glMaterialfv(GL_FRONT, GL_DIFFUSE, material_Kd);glMaterialfv(GL_FRONT, GL_SPECULAR, material_Ks);glMaterialfv(GL_FRONT, GL_EMISSION, material_Ke);glMaterialfv(GL_FRONT, GL_SHININESS, material_Se);

}

Tutorials

Compare three teapots

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Texture Mapping

Applying a 1-D, 2-D, or 3-D image to geometric primitivesTexture coordinates are called (s,t,r,q)

Uses of texturingSimulating materialsReducing geometric complexityReflectionsAdvanced surface properties

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Texture Mapping

s

t

x

y

z

image

geometry screen

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Applying Textures

The short version1. Specify a texture image

1. Read or generate image2. Assign to texture3. Enable texturing

2. Specify texture parameters1. Wrapping

1. How texture edges are handled2. Filtering

1. How texture sampling is handled

3. Assign texture coordinates to vertices

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Generating a Texture Identifier

Generate texture namesglGenTextures( n, *texIds );

A texture name is just an integerThe texture name is assigned to some texture

data later on Example

unsigned int texName;glGenTextures(1, &texname)

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Binding Textures

Bind textures before usingglBindTexture( target, id ); Binding a texture means assigning a certain texture id to a certain

kind of texture The valid kinds of textures are

GL_TEXTURE_1D GL_TEXTURE_2D GL_TEXTURE_3D

ExampleglBindTexture( GL_TEXTURE_2D, texName);

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Filter Modes Handles the sampling mode of the texture Minification or magnification

Handles when the texture to screen mapping is not 1:1 Special mipmap minification filters

Wrap Modes Handles texture lookups outside the texture’s edges Clamping

Copies data from the edge of the texture Repeating

Tiles the texture Texture Functions

How to mix primitive’s color with texture’s color Blend Modulate Replace

Texture Application Methods

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Filter Modes

Texture Polygon

Magnification Minification

PolygonTexture

Example:

glTexParameteri( glTexParameteri( target, type, modetarget, type, mode ); );

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Wrapping Mode

Example:

glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP )

glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT )

texture

s

t

GL_CLAMPwrapping

GL_REPEATwrapping

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Based on parametric texture coordinates Texture coordinates are assigned to vertices

Just like colours and normals The n-D to 3-D mapping is the responsibility of

the programmer/modeller glTexCoord*() specified at each vertex

s

t

Mapping Texture

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Texture Mapping

0, 0 1, 0

(0.4, 0.2)

(0.8, 0.4)

A

B C

a

bc

1, 10, 1

(s, t) = (0.2, 0.8)

Texture Space Object Space

Tutorials

Make checkerboard texture

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int i, j, c; for (i = 0; i < 64; i++) { for (j = 0; j < 64; j++) { c = ((((i&0x8)==0)^((j&0x8))==0))*255; checkImage[i][j][0] = (GLubyte) c; checkImage[i][j][1] = (GLubyte) c; checkImage[i][j][2] = (GLubyte) c; checkImage[i][j][3] = (GLubyte) 255; } }

Tutorials

Assign texture

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glGenTextures(1, &texName); glBindTexture(GL_TEXTURE_2D, texName);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 64, 64, 0, GL_RGBA, GL_UNSIGNED_BYTE, checkImage);

Tutorials

Texture mapping onto rectangle

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glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glEnable(GL_TEXTURE_2D); glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL); glBindTexture(GL_TEXTURE_2D, texName); glBegin(GL_QUADS); glTexCoord2f(0.0, 0.0); glVertex3f(-0.5, -0.5, 0.0); glTexCoord2f(0.0, 1.0); glVertex3f(0.5, -0.5, 0.0); glTexCoord2f(1.0, 1.0); glVertex3f(0.5, 0.5, 0.0); glTexCoord2f(1.0, 0.0); glVertex3f(-0.5, 0.5, 0.0); glEnd(); glFlush(); glDisable(GL_TEXTURE_2D);

Q&A

Any questions?

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