3D coordinate systems

X

Y

Z

Right-Hand Coordinate System

X

Y

Z

Left-Hand Coordinate System

OpenGL uses this! Direct3D uses this!

Visualizing in 3D

X

Y

Z

1.0

z=1.0

x=1.0

y=1.0

A B

CD

E F

GH

Counter-clockwise

Rendering a Box in OpenGL

• We render the 6 faces as polygons– Polygons are specified as a list of vertices– Vertices are specified in counterclockwise

order looking at the surface of the face!

A B

CD

E F

GH

OpenGL Polygon Rendering

GLdouble size = 1.0;

glBegin(GL_POLYGON); // front face glVertex3d(0.0, 0.0, size); glVertex3d(size, 0.0, size); glVertex3d(size, size, size); glVertex3d(0.0, size, size); glEnd();

OpenGL Conventions

• C library– All function names start with gl

• OpenGL is a retained mode graphics system– It has a state– glBegin(GL_POLYGON) puts us into a

polygon rendering state.

OpenGL Types

• Basic numeric types– GLdouble = double– GLfloat = float– GLint = int– GLshort = short

• Mostly you’ll use GLdouble and GLfloat

Function suffixes

• Many functions have alternatives– Alternatives are specified by the suffix– glVertex2d

• 2 double parameters• void glVertex2d(GLdouble x, GLdouble y);

– glVertex3f• 3 float parameters• void glVertex3f(GLfloat x, GLfloat y, GLfloat z);

– glVertex3fv• void glVertex3fv(const GLfloat *v);

All of dem…

• glVertex2d, glVertex2f, glVertex2i, glVertex2s, glVertex3d, glVertex3f, glVertex3i, glVertex3s, glVertex4d, glVertex4f, glVertex4i, glVertex4s, glVertex2dv, glVertex2fv, glVertex2iv, glVertex2sv, glVertex3dv, glVertex3fv, glVertex3iv, glVertex3sv, glVertex4dv, glVertex4fv, glVertex4iv, glVertex4sv

Specifying a color (no lighting)

• glColor3f(red, green, blue);

• Most of the same suffixes apply…

GLdouble size = 1.0; glColor3d(1.0, 0.0, 0.0); // red

glBegin(GL_POLYGON); // front face glVertex3d(0.0, 0.0, size); glVertex3d(size, 0.0, size); glVertex3d(size, size, size); glVertex3d(size, 0.0, size); glEnd();

Moving to 3D

• Camera Configuration

• Parameters

• Tessellation

• Scene Graphs

Structure of Our Programs

• OnGLDraw()– Clear the buffers– Set up the camera– Position the camera– Configure OpenGL– Render whatever we are rendering– Flush

Clear the Buffers

void CChildView::OnGLDraw(CDC *pDC){ // Clear to black... glClearColor(0.0f, 0.0f, 0.0f, 0.0f) ; glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

. . .

Camera Configuration

What does it take to describe a camera?

Describing a Camera

Where it is in space Eye location

Which way it’s pointing Or what it’s pointing at

Which way is up Zoom characteristics

Field of view angle

Setting up the Camera

Field of View(angle)

Near clipping plane

Far clipping plane

Nothing is rendered that is: Closer than the near clipping plane Farther than the far clipping plane

Aspect ratio = w/h

w

h

gluPerspective()

• void gluPerspective(GLdouble fovy, GLdouble aspect,

GLdouble zNear, GLdouble zFar );

• Fovy = Field of view angle– Degrees, usually less than 90

• Aspect = Ratio of width/height of window

• zNear = distance to near clipping plane• zFar = distance to far clipping plane

glu = GL Utility

Important

• What do the numbers zFar, zNear represent?– Always select some unit for your application

• Inches, Feet, Meters, etc.• In my sample application, I used inches

Using gluPerspective() // // Set up the camera //

glMatrixMode(GL_PROJECTION); glLoadIdentity();

// Determine the screen size so // we can determine the aspect ratio int width, height; GetSize(width, height); GLdouble aspectratio = GLdouble(width) / GLdouble(height);

// Set the camera parameters gluPerspective(25., // Field of view. aspectratio, // The aspect ratio. 10., // Near clipping 200.); // Far clipping

After this

• The camera is:– At the origin– Looking down the -Z axis

Positioning the Camera

• gluLookAt(eyex, eyey, eyez, atx, aty, atz, upx, upy, upz);

• Eye – Where the camera is located

• At – What the camera is looking at

• Up – Which direction is up– Can’t be the looking direction

Matrix Modes

• GL_PROJECTION– 3D to 2D conversion– Camera parameters

• GL_MODELVIEW– Translation, rotation, etc. of Graphical Models– gluLookAt is a rotation and translation of your

graphical model• the camera is really at the origin and looking down

the z axis.

Using gluLookAt()

// Set the camera location glMatrixMode(GL_MODELVIEW); glLoadIdentity();

gluLookAt(50., 50., 50., // eye x,y,z 0., 0., 0., // center x,y,z 0., 1., 0.); // Up direction

. . . Render from here on . . .

Some OpenGL Configurations

// // Some standard parameters //

// Enable depth test glEnable(GL_DEPTH_TEST);

// Cull backfacing polygons glCullFace(GL_BACK); glEnable(GL_CULL_FACE);

Example: Showing the coordinate axis…

if(m_showaxis) { glColor3d(0., 1., 1.);

glBegin(GL_LINES); glVertex3d(0., 0., 0.); glVertex3d(12., 0., 0.);

glVertex3d(0., 0., 0.); glVertex3d(0., 12., 0.);

glVertex3d(0., 0., 0.); glVertex3d(0., 0., 12.); glEnd(); }

Example: A Cubevoid CChildView::Cube(GLdouble size){ GLdouble a[] = {0., 0., size}; GLdouble b[] = {size, 0., size}; GLdouble c[] = {size, size, size}; GLdouble d[] = {0., size, size}; GLdouble e[] = {0., 0., 0.}; GLdouble f[] = {size, 0., 0.}; GLdouble g[] = {size, size, 0.}; GLdouble h[] = {0., size, 0.};

glColor3d(0.8, 0., 0.);

glBegin(GL_POLYGON); // Front glVertex3dv(a); glVertex3dv(b); glVertex3dv(c); glVertex3dv(d); glEnd(); . . .

a b

cd

e f

gh

See example program…