Introduction to OpenGL

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Introduction to OpenGL
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What is a Graphics API

• A software interface for graphics hardware.
• Provide the low-level functions to access
  graphics hardware directly.
• OpenGL / Direct3D
• (Direct3D also provides high-level functions.)

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API Hierarchy
Applications
GDI
OpenGL
Hardware Driver

Display Device
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What is OpenGL1/2

• Industry standard.
• Hardware independent.
• Window system independent.

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What is OpenGL2/2

• No commands for performing windowing tasks or
  obtaining user input are included.
• No high-level commands for describing models of
  3D objects are provided.

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What OpenGL provides

• Draw with points, lines, and polygons.
• Matrix Operations (Transformations)
• Hidden Surface Removal (Z-Buffer)
• Lighting (Phong model)
• Gouraud Shading
• Texture mapping
• Pixels operations

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The Buffers

• A buffer is a memory area in the graphics
  hardware for some special purposes.
• An OpenGL system can manipulate the four buffers
• Color buffers
• Depth buffer (Z-Buffer)
• Stencil buffer
• Accumulation buffer
• Will be discussed later.

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Rendering Pipeline1/2
OpenGL Command Buffer
OpenGL API Calls
Transformation and Lighting
Rasterization
Frame Buffer
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Rendering Pipeline2/2
Per-Vertex Operations and Primitive Assembly
Vertex Data
Evaluators
Per-Fragment Operations
Display List
Frame Buffer
Rasterization
Texture Assembly
Pixel Data
Pixel Operations
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OpenGL Relative Libraries1/2

• OpenGL Library
• The basic library to access the graphics
  hardware.
• GLU
• Provide some basic utilities based on the OpenGL
  library (camera model, NURBS).
• GLX / WGL / AGL
• OS dependent libraries to bind the OpenGL library
  with specific window system.
• GLX for X-window, WGL for win32, AGL for Apple.

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OpenGL Relative Libraries2/2

• GL, GLU, WGL libraries are already contained
  within the OS later than Win95SE.
• For Linux, FreeBSD systems, download the mesa
  library, which is fully compatible with OpenGL.

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OpenGL Utility Toolkit (GLUT) 1/3

• A window system-independent toolkit to hide the
  complexities of differing window system APIs.
• Use the prefix of glut. (ex glutDisplayFunc())
• Provide following operations
• Initializing and creating window
• Handling window and input events
• Drawing basic three-dimensional objects
• Running the program

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OpenGL Utility Toolkit (GLUT) 2/3

• Where to get GLUT?
• Win32
• http//www.xmission.com/nate/glut.html
• Linux
• http//www.mesa3d.org/

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OpenGL Utility Toolkit (GLUT) 3/3

• On Microsoft Visual C 6
• Put glut.h into ltMSVCgt/include/GL/
• Put glut.lib into ltMSVCgt/lib/
• Put glut32.dll into ltwindowgt/System32/
• On Microsoft Visual C .NET
• Put glut.h into ltMSVCgt/platformSDK/include/GL/
• Put glut.lib into ltMSVCgt/platformSDK/lib/
• Put glut32.dll into ltwindowgt/System32/

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How to Compile1/3

• On Microsoft Visual C 6
• Create a new Project with Win32 Console
  Application
• Open Project Settings dialog and add opengl32.lib
  glu32.lib glut32.lib into Link/Objects/library
  modules.
• Writing your OpenGL code.
• Compile it.

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How to Compile2/3

• On Microsoft Visual C .NET
• New a Win32 Project
• Add opengl32.lib glu32.lib glut32.lib into
  link/library dependence.
• Writing your OpenGL code.
• Compile it.

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How to Compile3/3

• On UNIX
• Needed libraries
• libGL.so, libGLU.so, libglut.a, libX11.a,
  libX11.so
• Compile command
• gcc OpenGL code files o output file lglut
  lGLU lGL lX11 lm

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The Simplest Program1/3

• include ltGL/glut.hgt
• void GL_display()
• glClearColor(0.0f, 0.0f, 0.0f, 0.0f)
• glClear(GL_COLOR_BUFFER_BIT)
• glColor3f(1.0f, 1.0f, 1.0f)
• glutSolidCube(1.0)
• glFlush()
• void GL_reshape(GLsizei w, GLsizei h)
• glViewport(0, 0, w, h)
• glMatrixMode(GL_PROJECTION)
• glLoadIdentity()
• glOrtho(-2.0f, 2.0f, -2.0f, 2.0f, -2.0f, 2.0f)
• glMatrixMode(GL_MODELVIEW)
• glLoadIdentity()

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The Simplest Program2/3

• void main(void)
• glutInitDisplayMode(GLUT_SINGLE GLUT_RGB)
• glutCreateWindow("Sample")
• glutDisplayFunc(GL_display)
• glutReshapeFunc(GL_reshape)
• glutMainLoop()

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The Simplest Program3/3
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Reference1/2

• Official site of OpenGL
• http//www.opengl.org
• Useful Sites
• NeHes OpenGL Tutorials
• The Developers Gallery
• NVidias developer web

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Reference2/2

• Further Reading
• OpenGL Programming Guide (Red Book)
• OpenGL Reference Manual (Blue Book)

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Any Question

• ?