An Introduction to OpenGL programming

1. OpenGL Training/Tutorial
Jayant Mukherjee
1 February 13, 2013

2. Part01: Introduction
Introduction of OpenGL with code samples.
2 Part 01 - Introduction February 13, 2013

3. Part01 : Topics
 About OpenGL
 OpenGL Versions
 OpenGL Overview
 OpenGL Philosophy
 OpenGL Functionality
 OpenGL Usage
 OpenGL Convention
 OpenGL Basic Concepts
 OpenGL Rendering Pipeline
 Primitives (Points, Lines, Polygon)
 Environment Setup
 Code Samples (Win32/glut)
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4. Part01 : About OpenGL
 History
 OpenGL is relatively new (1992) GL from Silicon Graphics
 IrisGL - a 3D API for high-end IRIS graphics workstations
 OpenGL attempts to be more portable
 OpenGL Architecture Review Board (ARB) decides on all
enhancements
 What it is…
 Software interface to graphics hardware
 About 120 C-callable routines for 3D graphics
 Platform (OS/Hardware) independent graphics library
 What it is not…
 Not a windowing system (no window creation)
 Not a UI system (no keyboard and mouse routines)
 Not a 3D modeling system (Open Inventor, VRML, Java3D)
http://en.wikipedia.org/wiki/OpenGL
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5. Part01 : OpenGL Versions
Version Release Year
OpenGL 1.0 January, 1992
OpenGL 1.1 January, 1997
OpenGL 1.2 March 16, 1998
OpenGL 1.2.1 October 14, 1998
OpenGL 1.3 August 14, 2001
OpenGL 1.4 July 24, 2002
OpenGL 1.5 July 29, 2003
OpenGL 2.0 September 7, 2004
OpenGL 2.1 July 2, 2006
OpenGL 3.0 July 11, 2008
OpenGL 3.1 March 24, 2009 and updated May 28, 2009
OpenGL 3.2 August 3, 2009 and updated December 7, 2009
OpenGL 3.3 March 11, 2010
OpenGL 4.0 March 11, 2010
OpenGL 4.1 July 26, 2010
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6. Part01 : Overview
 OpenGL is a procedural graphics language
 programmer describes the steps involved to achieve a
certain display
 “steps” involve C style function calls to a highly portable
API
 fairly direct control over fundamental operations of two
and three dimensional graphics
 an API not a language
 What it can do?
 Display primitives
 Coordinate transformations (transformation matrix
manipulation)
 Lighting calculations
 Antialiasing
 Pixel Update Operations
 Display-List Mode
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7. Part01 : Philosophy
 Platform independent
 Window system independent
 Rendering only
 Aims to be real-time
 Takes advantage of graphics hardware where it
exists
 State system
 Client-server system
 Standard supported by major companies
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8. Part01 : Functionality
 Simple geometric objects
(e.g. lines, polygons, rectangles, etc.)
 Transformations, viewing, clipping
 Hidden line & hidden surface removal
 Color, lighting, texture
 Bitmaps, fonts, and images
 Immediate- & Retained- mode graphics
 An immediate-mode API is procedural. Each time a new
frame is drawn, the application directly issues the drawing
commands.
 A retained-mode API is declarative. The application
constructs a scene from graphics primitives, such as
8 shapes and lines. Part 01 - Introduction February 13, 2013

9. Part01 : Usage
 Scientific Visualization
 Information
Visualization
 Medical Visualization
 CAD
 Games
 Movies
 Virtual Reality
 Architectural
Walkthrough
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10. Part01 : Convention
 Constants:
 prefix GL + all capitals (e.g. GL_COLOR_BUFER_BIT)
 Functions:
 prefix gl + capital first letter (e.g. glClearColor)
 returnType glCommand[234][sifd] (type value, ...);
 returnType glCommand[234][sifd]v (type *value);
 Many variations of the same functions
 glColor[2,3,4][b,s,i,f,d,ub,us,ui](v)
 [2,3,4]: dimension
 [b,s,i,f,d,ub,us,ui]: data type
 (v): optional pointer (vector) representation
Example:
glColor3i(1, 0, 0)
or
glColor3f(1.0, 1.0, 1.0)
or
GLfloat color_array[] = {1.0, 1.0, 1.0};
glColor3fv(color_array)
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11. Part01 : Basic Concepts
 OpenGL as a state machine (Once the value of a
property is set, the value persists until a new value is
given).
 Graphics primitives going through a “pipeline” of
rendering operations
 OpenGL controls the state of the pipeline with many state
variables (fg & bg colors, line thickness, texture
pattern, eyes, lights, surface material, etc.)
 Binary state: glEnable & glDisable
 Query: glGet[Boolean,Integer,Float,Double]
 Coordinates :
XYZ axis follow Cartesian system.
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12. Part01 : Rendering Pipeline
Primitives Transformation Clipping Shading Projection Rasterisation
Primitives Transformation Clipping Shading/Texturing Projection Rasterisation
• Lines, Polygons, Triangles • Modeling Transform • Parallel/Orthographic • Material, Lights • Viewport location • Images in buffer
• Vertices (Transform Matrix) • Perspective • Color • Transformation • Viewport Transformation
• Viewing Transform • Images on screen
(Eye, Lookat)
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13. Part01 : Primitives (Points, Lines…) - I
 All geometric objects in OpenGL are created from a set of basic
primitives.
 Certain primitives are provided to allow optimization of geometry for
improved rendering speed.
 Primitives specified by vertex calls (glVertex*) bracketed by
glBegin(type) and glEnd()
 Specified by a set of vertices
 glVertex[2,3,4][s,i,f,d](v) (TYPE coords)
 Grouped together by glBegin() & glEnd()
 glBegin(GLenum mode)
glBegin(GL_POLYGON)  mode includes
 GL_POINTS
glVertex3f(…)  GL_LINES, GL_LINE_STRIP, GL_LINE_
LOOP
glVertex3f(…)  GL_POLYGON
glVertex3f(…)  GL_TRIANGLES, GL_TRIANGLE_STRI
P
glEnd  GL_QUADS, GL_QUAD_STRIP
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14. Part01 : Primitives (Points, Lines…) - II
 Point Type
 GL_POINTS
 Line Type
 GL_LINES
 GL_LINE_STRIP
 GL_LINE_LOOP
 Triangle Type
 GL_TRIANGLES
 GL_TRIANGLE_STRI
P
 GL_TRIANGLE_FAN
 Quad Type
 GL_QUADS
 GL_QUAD_STRIP
 Polygon Type
 GL_POLYGON
Ref : Drawing Primitives in OpenGL
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15. Part01 : Environment Setup
 Using Windows SDK
 OpenGL and OpenGL Utility (GLU) ships with Microsoft SDK.
Add SDK Path to IDE Project Directories.
 Add Headers: gl.h, glu.h
Found @ <SDKDIR>Windowsv6.0Aincludegl
 Add Libs for linking: opengl32.lib, glu32.lib
Found @ <SDKDIR>Windowsv6.0Alib
 Required DLLs: opengl32.dll, glu32.dll
Found @ <WINDIR> System32
 Using GLUT (www.xmission.com/~nate/glut.html or http://freeglut.sourceforge.net)
 Store the Binaries at appropriate location and reference it properly
 Add Header: glut.h
Found @ <GLUTPATH>include
 Add Lib for linking: glut32.lib
Found @ <GLUTPATH>lib
 Required DLL: glut32.dll
Found @ <GLUTPATH>bin
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16. Part01 : Code Samples
 Using Windows SDK
 Create Basic Window from the Windows Base Code.
 Add Headers & Libs.
 Modify the Windows Class Registration.
 Modify the Window Creation Code.
 Setup PixelFormat.
 Create Rendering Context and set it current.
 Add Cleanup code where remove rendering context.
 Add Event Handlers
 Add Display function handler for rendering OpenGL stuff.
 Add Resize function handler for window resizing.
 Using GLUT
 Add Headers and Libs.
 Initialize the GLUT system and create basic window.
 Add Event Handlers
 Add Display, Resize, Idle, Keyboard, Mouse handlers.
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17. Part02: Basics
Introduction of OpenGL with code samples.
17 Part 02 - Basics February 13, 2013

18. Part02 : Topics
 Transformations
 Modeling
 Concept of Matrices.
 Scaling, Rotation, Translation
 Viewing
 Camera
 Projection: Ortho/Perspective
 Code Samples (Win32/glut)
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19. Part02 : Transformations-Modeling I
 Concept of Matrices.
 All affine operations are matrix multiplications.
 A 3D vertex is represented by a 4-tuple (column) vector.
 A vertex is transformed by 4 x 4 matrices.
 All matrices are stored column-major in OpenGL
 Matrices are always post-multiplied. product of matrix and
vector is Mv. OpenGL only multiplies a matrix on the
right, the programmer must remember that the last matrix
specified is the first applied.
x
m0 m4 m8 m12
 y
v M
m1 m5 m9 m13
z m2 m6 m10 m14
w m3 m7 m11 m15
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20. Part02 : Transformations-Modeling II
 OpenGL uses stacks to maintain transformation matrices
(MODELVIEW stack is the most important)
 You can load, push and pop the stack
 The current transform is applied to all graphics primitive until it is
changed
2 ways of specifying Transformation Matrices.
 Using crude Matrices.  Using built-in routines.
 Specify current Matrix  glTranslate[f,d](x,y,z)
glMatrixMode(GLenum mode)  glRotate[f,d](angle,x,y,z)
 Initialize current Matrix  glScale[f,d](x,y,z)
glLoadIdentity(void)  Order is important
glLoadMatrix[f,d](const TYPE
*m)
 Concatenate current Matrix
glMultMatrix(const TYPE *m)
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21. Part02 : Transformations-Viewing I
 Camera.
 Default: eyes at origin, looking along -Z
 Important parameters:
 Where is the observer (camera)? Origin.
 What is the look-at direction? -z direction.
 What is the head-up direction? y direction.
 gluLookAt(
eyex, eyey, eyez, aimx, aimy, aimz, upx, upy, upz )
 gluLookAt() multiplies itself onto the current matrix, so it usually
comes after glMatrixMode(GL_MODELVIEW) and
glLoadIdentity().
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22. Part02 : Transformations-Viewing II
 Projection
 Perspective projection
 gluPerspective( fovy, aspect, zNear, zFar )
 glFrustum( left, right, bottom, top, zNear, zFar )
 Orthographic parallel projection
 glOrtho( left, right, bottom, top, zNear, zFar )
 gluOrtho2D( left, right, bottom, top )
 Projection transformations
(gluPerspective, glOrtho) are left handed
 Everything else is right handed, including the y
vertexes to be rendered y z+
x
x
left handed z right
+ handed
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23. Part02 : Transformations-Viewing III
 glFrustum(left, right, bottom, top, zNear, zFar)
 gluPerspective(fovy, aspect, zNear, zFar)
 glOrtho(left, right, bottom, top, zNear, zFar)
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24. Part02 : Code Samples
Ortho Perspective
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