WHAT IS OPENGL

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WHAT IS OPENGL
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What is OpenGL

• OpenGL provides the programmer with an interface
  to graphics hardware. It is a powerful, low level
  rendering and modelling software library,
  available on all major platforms, with wide
  hardware support.

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OpenGL History

• Developed by Slicon Graphics, Inc (SGI) in 1992.
• Development still has been overseen by the OpenGL
  Architecture Review Board (ARB), made up of ATI,
  Compaq, EvansSutherland, HP, IBM, Intel,
  Intergraph, nVidia, Microsoft and SG.

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What can be done with OpenGL

• Games

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What can be done with OpenGL

• Simulators

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What can be done with OpenGL

• Medical Applications

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What can be done with OpenGL

• CAD Programs

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What can be done with OpenGL

• Animated Movies

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What can be done with OpenGL

• OS GUIs

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How Can I use OpenGL?

• You can use OpenGL in all main OSs.
• You have to know Ansi C, C, Pascal, Visual
  Basic or Java.
• Good knowledge of mathematics, physics.
• Think 3D.

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Start Constructing 3D World
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Drawing In Space

• Every object in space constructed from geometric
  primitives that are specified by vertices

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Points
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Lines
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Line Loop
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Line Strip
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Triangles
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Triangle Fan
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Triangle Strip
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Quads
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Quad Strip
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Polygon
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What can be done with these primitives?

• Terrain for simulators

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What can be done with these primitives?

• Objects,scenes

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What can be done with these primitives?

• Animated Objects

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Object Modes

• Point
• Line (wireframe)
• Fill (solid)

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Viewing

• Users eye can be considered as camera. Camera
  considered as view and 3D world and objects are
  considered as model. They together considered
  as modelview. Moving camera is equivalent to
  moving every object in the world towards a
  stationary camera

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Camera Analogy

• 3D is just like taking a photograph (lots of
  photographs!)

viewing volume
camera
model
tripod
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Projections

• Every point in 3D world projected on 2D scene.
  Thats how we see 3D world on computer screen or
  on paper. OpenGL uses two projection type.
• Perspective Projection
• Ortographic Projection

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Moving Camera (Use gluLookAT)
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Moving Camera (Use gluLookAT)
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Moving Model (Use glTranslatef, glRotatef,
glScalef)
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Moving Model (Use glTranslatef, glRotatef,
glScalef)
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Perspective Projection

• Better for human vieving system.

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Orthogonal Projection

• Useful for CAD applications.(Blueprints)

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Color

• Color has 3 or 4 components. Namely red value,
  green value, blue value and alpha (transperency)
  value.
• glColor3f(1,0,0)red colored object
• glColor3f(1,1,1)white color
• glColor3b(0,255,0)green color
• glColor4f(0,0,1,0.3) Transperent object in green
  color

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Light

• Light is a magic in CG world. It makes the
  objects look real.

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Lighting Principles

• Lighting simulates how objects reflect light
• material composition of object
• lights color and position
• global lighting parameters
• ambient light
• two sided lighting
• available in both color indexand RGBA mode

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How OpenGL Simulates Lights

• Phong lighting model
• Computed at vertices
• Lighting contributors
• Surface material properties
• Light properties
• Lighting model properties

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SurfaceNormals

• Normals define how a surface reflects light
• glNormal3f( x, y, z )
• Current normal is used to compute vertexs color
• Use unit normals for proper lighting
• scaling affects a normals length
• glEnable( GL_NORMALIZE ) orglEnable(
  GL_RESCALE_NORMAL )

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Material Properties

• Define the surface properties of a primitive
• glMaterialfv( face, property, value )
• separate materials for front and back

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Light Sources (cont.)

• Light color properties
• GL_AMBIENT
• GL_DIFFUSE
• GL_SPECULAR

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Material Properties
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LightMaterial
Light position changed, ambient and diffuse
components changed
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LightMaterial
Light position changed, ambient and diffuse
components changed, Material properties changed
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Effect of Light
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Texture Mapping

• Texture mapping is probably the most significant
  advance in computer graphics in the last 10
  years. OpenGL provides texture image mapping
  functions that fit images onto polygons in your
  scene. How those images are put onto the polygons
  is up to you.

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Texture Mapping

• Realistic images
• Anti-aliased text
• Simulating reflective surfaces like mirrors or
  polished floors
• Simulating materials like wood, bricks or granite
• Reducing the complexity ( number of polygons ) of
  a geometric object
• Image processing techniques like image warping
  and rectification, rotation and scaling

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Texture Mapping
1000 Polygons with texture
3000 Polygons without texture
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Texture Mapping
screen
geometry
image
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Texture Mapping
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Texture Mapping
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Texture Mapping
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Texture Mapping
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Fog

• Fog works in two modes
• Linear fog mode is used for depth cueing affects.
  In this mode, you provide OpenGL with a starting
  and ending distance from the eye, and between
  those distances, the fog color is blended into
  the primitive in a linear manner based on
  distance from the eye.
• Exponential fog mode is used for more natural
  environmental affects like fog, smog and smoke.
  In this mode, the fogs density increases
  exponentially with the distance from the eye. For
  these modes, the coefficient is computed as

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Linear Fog
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Exponential Fog
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Exponential 2 Fog
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Beyond Lines and Points
GLU32 Library provides some preformed objects
that are not included in OpenGL. They are
sphere, dodacahedron, tetrahedron, cube, cone,
octahedron, teapot and torus.
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Beyond Lines and Points

• GLU32 library also provides some functions to
  draw curves and surfaces without dividing them
  into smaller triangles. Bezier and NURBs
  (Non-uniform b-splines) are used for this

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Buffers

• A buffer in OpenGL is essentially a
  two-dimensional array of values that correspond
  to pixels in a window or offscreen image. Each
  buffer has the same number of columns and
  rows(width and height) as the current client area
  of a window but holds a different range and type
  of values.

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Buffers

• Color Buffer
• Double Buffering
• Stereo Buffering
• Depth Buffer
• Stencil Buffer
• Accumulation Buffer

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Color Buffer

• The color buffer holds pixel color information.
  Each pixel can contain a red/green/blue/alpha
  values that describe the appearance of that
  pixel.
• Double Bufferingprovides an additional offscreen
  color buffer that is often used for animation. It
  eliminates the annoying flicker
• Stereo Bufferingprovides an additional color
  buffer in single-buffered mode and two additional
  color buffers in double-buffered mode to generate
  a left- and right-eye screen image. You can
  create true three-dimensional images by choosing
  the correct viewing positions for each eye.

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Depth Buffer

• Holds distance values for each pixel.
• Usually use for performing hidden surface
  removal.

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Stencil Buffer

• Block out certain areas on screen.(Usefull for
  drawing instruments on flight sims).

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Accumulation Buffer

• Motion blur
• Full-screen anti-aliasing

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Extensions

• OpenGL extensions allow vendors to provide
  product-specific features within OpenGL without
  breaking compatibility with applications or other
  vendor hardware.
• In general, only use extensions when you have to,
  and then, use a generalized (ARB or EXT type)
  extensions and not a vendor-specific one.
• Do not forget to check any extension before you
  start your application.

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Extensions
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Display Lists vs Immediate Mode

• Mainly used for performance issues.
• Display list is precompiled list of OpenGL
  commands.
• Create an object using display list call it any
  time you need.
• glcalllist(bolt)

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Hints For Using OpenGL

• FPS (frame per second) should not be less than
  25.
• Always use double-buffering.
• Always use triangles not polygons.
• Do not use convex polygons.
• Use LOD (Level of detail).
• Do not render images that are not in viewing
  volume.

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Direct X

• DirectX is Microsofts attempt at a set of APIs
  that provide direct access to hardware in
  Windows OS.
• DirectDraw
• Direct3D
• DirectInput (handle game devices)
• DirectSound
• DirectMusic
• DirectPlay (comm, network, internet)
• DirectShow (Avi, mpeg support)

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Directx vs OpenGL
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Directx vs OpenGL
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Thanks for listening.

• Questions and Answers.