CS380 LAB II OpenGL

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CS380 LAB II OpenGL

• Bochang Moon
• Reference1. OpenGL course slides by Rasmus
  Stenholt
• Reference2. http//nehe.gamedev.net/

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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

• Transformations
• Modeling Transformations
• Draw 3D objects
• Translate
• Rotate
• Scale

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Transformations

• All transformations in OpenGL are carried out by
  matrices
• There are different matrices for different
  purposes
• The modelview matrix
• GL_MODELVIEW
• The projection matrix
• GL_PROJECTION
• The texture matrix
• GL_TEXTURE
• All matrices are post-multiplied
• I.e. the current matrix M becomes MN when N is
  performed
• Post-multiplication is closely linked to matrix
  stacks

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Transformations

• Matrices
• All matrices in OpenGL are 4x4
• Why use 4-D matrices for 3-D graphics?
• A 4x4 matrix can rotate and translate the same
  vector in one operation
• A 4x4 matrix can make the otherwise non-linear
  perspective projection linear
• Modern CPUs are very efficient at handling 4x4
  matrices

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Transformations

• Specify which matrix is the current matrix
• Mode
• GL_MODELVIEW
• Applies subsequent matrix operations to the model
  view matrix stack
• GL_PROJECTION
• Applies subsequent matrix operations to the
  projection matrix stack
• etc.

void glMatrixMode( GLenum   mode)
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Set a view
int main( int argc, char argv )
glutReshapeFunc( reshape )
void reshape(int width, int height)
glViewport(0, 0, width, height)
glMatrixMode(GL_PROJECTION)
glLoadIdentity()
double aspect width/double(height)
gluPerspective(45, aspect, 1, 1024)
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Set a view
glMatrixMode(GL_PROJECTION)
glLoadIdentity()
double aspect width/double(height)
gluPerspective(45, aspect, 1, 1024)
void gluPerspective( GLdouble   fovy,
  GLdouble   aspect,
  GLdouble   zNear,
  GLdouble   zFar)

• fovy
• View angle, in degrees, in the y direction
• aspect
• Ratio of x (width) to y (height)
• zNear
• Distance from the viewer to the near clipping
  plane (positive)
• zFar
• Distance from the viewer to the far clipping
  plane (positive)

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Set a view

• Detailed explanations about Viewing
  Transformation will be provided in the next
  week.

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Draw 3D objects

• Use a set of OpenGL primitives
• e.g.,
• glBegin(GL_TRIANGLES)
• glVertex3f( 0.0f, 1.0f, 0.0f)
• glVertex3f(-1.0f,-1.0f, 0.0f)
• glVertex3f( 1.0f,-1.0f, 0.0f)
  
• glEnd()
• glBegin(GL_TRIANGLES)
• glEnd()

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Draw 3D objects

• GLUT provide simple 3D objects
• e.g., Teapot object
• void glutSolidTeapot(GLdouble size)
• void glutWireTeapot(GLdouble size)

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Draw 3D objects

• void display()
• glClear(GL_COLOR_BUFFER_BIT
  GL_DEPTH_BUFFER_BIT)
• glMatrixMode(GL_MODELVIEW)
• glLoadIdentity()
• glTranslatef(0,0,-1.0)
• glColor3f(r,g,b)
• glutWireTeapot(0.5)
• glFlush()

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Translations

• Multiply the current matrix by a translation
  matrix
• x, y, z
• Specify the x, y, and z coordinates of a
  translation vector

void glTranslatef( GLfloat   x,
  GLfloat   y,
  GLfloat   z)
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Translations

• Multiply the current matrix by a translation
  matrix

void glTranslatef( GLfloat   x,
  GLfloat   y,
  GLfloat   z)
1 0 0 X
0 1 0 Y
0 0 1 Z
0 0 0 1
Translation matrix (4x4)
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Review of Translations

• glMatrixMode(GL_MODELVIEW)
• glLoadIdentity()
• glTranslatef(0,0,-1.0)

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Review of Translations

• glMatrixMode(GL_MODELVIEW)
• glLoadIdentity()
• glTranslatef(0,0,-1.0)

Model view matrix
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Review of Translations

• glMatrixMode(GL_MODELVIEW)
• glLoadIdentity()
• glTranslatef(0,0,-1.0)

1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1
Model view matrix
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Review of Translations

• glMatrixMode(GL_MODELVIEW)
• glLoadIdentity()
• glTranslatef(0,0,-1.0)

1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1
1 0 0 0
0 1 0 0
0 0 1 -1
0 0 0 1
1 0 0 0
0 1 0 0
0 0 1 -1
0 0 0 1
Model view matrix
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Review of Translations

• glMatrixMode(GL_MODELVIEW)
• glLoadIdentity()
• glTranslatef(0,0,-1.0)
• glTranslatef(0,0,-1.0)

Again??
1 0 0 0
0 1 0 0
0 0 1 -1
0 0 0 1
1 0 0 0
0 1 0 0
0 0 1 -2
0 0 0 1
1 0 0 0
0 1 0 0
0 0 1 -1
0 0 0 1
Model view matrix
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Review of Translations

• void display()
• glClear(GL_COLOR_BUFFER_BIT
  GL_DEPTH_BUFFER_BIT)
• glMatrixMode(GL_MODELVIEW)
• glLoadIdentity()
• glTranslatef(0,0,-1.0)
• glTranslatef(0,0,-1.0)
• glColor3f(r,g,b)
• glutWireTeapot(0.5)
• glFlush()

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Tutorials

• Move your teapot based on key inputs
• l left
• r right
• u up
• d down
• f move out
• n move in

l
f
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Tutorials
void keyboard(unsigned char key, int x, int y)
if (key 'l') xpos - 0.1 else if
(key 'r') xpos 0.1 else if (key
'u') ypos 0.1 else if (key
'd') ypos - 0.1 else if (key 'f')
zpos - 0.1 else if (key 'n')
zpos 0.1 glutPostRedisplay()
float xpos 0.0 float ypos 0.0 float zpos
-2.0
void display() glTranslatef(xpos,ypos,zpos)

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Rotations
void glRotatef( GLfloat   angle,
  GLfloat   x,
  GLfloat   y,
  GLfloat   z)

• angle
• angle of rotation, in degrees
• x, y, z
• x, y, and z coordinates of a vector, respectively
• Normalized vector (If not, GL will normalize it)

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Rotations
void glRotatef( GLfloat   angle,
  GLfloat   x,
  GLfloat   y,
  GLfloat   z)
? ? ? 0
? ? ? 0
? ? ? 0
0 0 0 1
The questions will be resolved in the CS380
lecture Modeling Transformations.
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Rotations

• void display()
• glTranslatef(xpos,ypos,zpos)
  
• glRotatef(30,0,0,1)

30 degrees rotation based on a normalized vector
(0, 0, 1)
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Tutorials

• Rotate your teapot on X axis
• e.g., 30, 60, and 90 degrees

30 degrees
90 degrees
60 degrees
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Tutorials

• 30 degrees on X axis
• glRotatef(30,1,0,0)
• 60 degrees on X axis
• glRotatef(60,1,0,0)
• 90 degrees on X axis
• glRotatef(90,1,0,0)

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Scaling

• x, y, z
• scale factors along the x, y, and z axes,
  respectively

void glScalef( GLfloat   x,
  GLfloat   y,
  GLfloat   z)
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Scaling
void glScalef( GLfloat   x,
  GLfloat   y,
  GLfloat   z)
X 0 0 0
0 Y 0 0
0 0 Z 0
0 0 0 1
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Scaling
void display() glLoadIdentity()
glTranslatef(0,0,-3)
glScalef(2,1,1)
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Review of Scaling
void display() glLoadIdentity()
glTranslatef(0,0,-3)
glScalef(2,1,1)
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1
Model view matrix
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Review of Scaling
void display() glLoadIdentity()
glTranslatef(0,0,-3)
glScalef(2,1,1)
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1
1 0 0 0
0 1 0 0
0 0 1 -3
0 0 0 1
1 0 0 0
0 1 0 0
0 0 1 -3
0 0 0 1
Model view matrix
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Review of Scaling
void display() glLoadIdentity()
glTranslatef(0,0,-3)
glScalef(2,1,1)
2 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1
2 0 0 0
0 1 0 0
0 0 1 -3
0 0 0 1
1 0 0 0
0 1 0 0
0 0 1 -3
0 0 0 1
Model view matrix
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Questions

• Why use 4-D matrices for 3-D graphics?
• Combine multiple transformations into a 4x4
  matrix

2 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1
2 0 0 0
0 1 0 0
0 0 1 -3
0 0 0 1
1 0 0 0
0 1 0 0
0 0 1 -3
0 0 0 1
Model view matrix
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Next time

• Viewing Transformation in OpenGL