3D Computer Graphics

1

• 3D Computer Graphics
• OpenGL

David Kabala
2
Why Cool?
3
Computer Graphics

• Raster Graphics
• Images are created from pixel data
• Vector Graphics
• Images are created from primitives of points,
  lines, curves, and other shapes
• Final image is computed by processing this
  representation

4
OpenGL

• OpenGL is a mixture of Vector and Raster graphics
• Vector graphics
• polygons, surface normals, colors, etc.
• Raster graphics
• textures(images) that are mapped onto surfaces
• Rasterizing vector graphics into frame buffer
• Most platforms have an implementation of OpenGL
• Windows, Linux, Mac, iPhone, Android, PS3, and
  many more

5
OpenGL Rendering Pipeline
Vector Operations
Rasterization
Data
Fragment Operations
Frame Buffer
6
OpenGL Rendering Pipeline
7
OpenGL Rendering Pipeline

• ATI R600 Pipeline

8
OpenGL Changing with 3.0

• Many parts of the OpenGL API have been deprecated
  in version 3.0, and removed in version 3.1
• This includes much of the fixed functionality of
  the pipeline
• Lighting
• Programing these portions in the pipeline is the
  path forward

9
OpenGL as a state machine

• OpenGL is organized for functional programming
  not object-oriented
• Stays in a persistent state until it receives a
  message that tells it to change
• Objects are bound
• Changes are made to the state
• Color, lighting, line width, etc
• Immediate draw mode

10
OpenGL API

• All methods are prefixed with gl
• e.g. glEnable(GLbool), glVertex2i(GLint,GLint)?
• All Types are prefixed with GL
• e.g. GLbool, GLint, GLflaot, GLenum
• All constants are prefixed with GL_
• e.g. GL_POINTS, GL_CULL_FACE, GL_QUADS

11
OpenGL defined types

• Important Types
• GLshort
• 16 bit integer
• GLint
• 32 bit integer
• GLfloat
• 32 bit floating point
• GLdouble
• 64 bit floating point
• GLboolean
• 8 bit unsigned integer
• GLenum
• 32 bit unsigned integer

• C/C leave the number of bytes of each type up
  to the compiler writer
• OpenGL has defined types that are the same size
  in all implementations

12
Drawing

• Primitives are drawn by sending vertex positions
  inside of a glBegin and glEnd block
• Example

void display(void)? //Setup state to start
drawing //points glBegin(GL_POINTS)
//Draw a point at 10,10
glVertex2i(10,10) glEnd()
13
glBegin/glEnd block

• OpenGL receives primitive geometry data inside
  a glBegin and glEnd block
• glBegin(GLenum primitiveType)?
• primitiveType argument takes a GLenum value of
  the type of primitives to draw

void display(void)? glBegin(GL_POINTS)
glVertex2i(10,10)
glVertex2i(20,10) glVertex2i(0,0)
glEnd() glVertex2i(10,0) //Will not draw
14
GlVertex variations

• Some sets of OpenGL methods take multiple
  numbers and types of arguments

glVertex2i
Number of arguments
Type of argument
15
Primitives

• Points
• Lines
• Triangles
• Quadrilaterals
• Polygons

16
Points

• send GL_POINTS as parameter to glBegin
• Every glVertex produces a single point
• Changing point drawing parameters
• glPointSize(GLint size)

void display(void)? //Setup state to start
drawing //points glPointSize(5.0)
glBegin(GL_POINTS) //Draw a point at
10,10 glVertex2i(10,10) glEnd()
17
Lines

• Line Draw Modes
• GL_LINES
• GL_LINE_STRIP
• Changing line width
• glLineWidth(GLint size)

• GL_LINE_LOOP

v1
v2
v2
v1
v5
v4
v3
v2
v4
v3
v1
18
Triangles

• GL_TRIANGLES
• GL_TRIANGLE_STRIP

• GL_TRIANGLE_FAN

19
Quads

• GL_QUADS
• GL_QUAD_STRIP

20
Polygons
v3

• GL_POLYGONS
• Must be convex
• Must be non-intersecting
• Separate polygonsmust be in separateglBegin/glEn
  d blocks

v2
v4
v5
v1
v2
v3
v1
v4
v5
v8
v6
v6
21
Next Time

• Using GLUT (OpenGL Utility) to manage window and
  context creation
• Transformations using matrix and vector algebra