What Is OpenGL?
OpenGl: - OpenGL (Open Graphics Library) is a cross-language, multi-platform application programming interface (API) for rendering 2D and 3D vector graphics. The API is typically used to interact with a Graphics processing unit (GPU), to achieve hardware-accelerated rendering.
OpenGL was developed by Silicon Graphics Inc. (SGI) from 1991 and released in January 1992 and is widely used in CAD, virtual reality, scientific visualization, information visualization, flight simulation, and video games. OpenGL is managed by the non-profit technology consortium Khronos Group.
Version
OpenGL 1.1
Release Date: March 4, 1997
OpenGL 1.2
Release Date: March 16, 1998
OpenGL 1.2.1
Release Date: October 14, 1998
OpenGL 1.3
Release Date: August 14, 2001
OpenGL 1.4
Release date: July 24, 2002
OpenGL 1.5
Release date: July 24, 2002
OpenGL 2.0
Release Date: September 7, 2004
OpenGL 2.1
Release Date: July 2, 2006
OpenGL 3.0
Release Date: August 11, 2008
OpenGL 3.1
Release Date: March 24, 2009
OpenGL 3.2
Release Date: August 3, 2009
OpenGL 3.3
Release Date: March 11, 2010
OpenGL 4.0
Release Date: March 11, 2010
OpenGL 4.1
Release Date: July 26, 2010
OpenGL 4.2
Release Date: August 8, 2011
OpenGL 4.3
Release Date: August 6, 2012
OpenGL 4.4
Release Date: July 22, 2013
Required• Knowledge in C\C++
• Dev C++ : a freeware for C/C++
http://www.bloodshed.net/devcpp.html• Glut Dev Pack
Setting OpenGL Dev Pack
1. To use Open GL install the correct version of glut DevPack go to
http://www.nigels.com/glt/devpak: download glut.3.7.6+.DevPak to a local folder
2. In Dev C++ open the package manager: Tools->Package Manager
3. Install the glut package: Package->Install Package
4. Browse to the local location where the package was downloaded to follow the installation wizard
5. The glut package should now appear in the main pane
6. Exit package manager
Setting Project for OpenGL
1. To compile, build and run using Dev C++: make a new project: File -> New -> Project and choose empty project and and C++ project is selected.
2. Create the new project in the folder with the source file.
3. Add the .cpp file to the project: Project -> add to project: select the .cpp file
4. Define the linker options: Project -> Project options
5. In the Parameters tab window add the following line in the Linker pane: -/glut32 -/glu32 -/opengl32 -/winmm -/gdi32
6. click ok
7. Compile and run the project:
8. Execute -> Compile & run
Various Pieces
•
gl: The basic libraries.
•
glu: Advanced implementation of OpenGL.
Higher level function calls/commands. i.e.
gluSphere.
•
glut: Generic platform independent library.
Hello World.cpp
#include <gl/glut.h>
void display( )
{
// nothing to see here, please move along
}
int main(int argc, char* argv[])
{
glutInit( &argc, argv );
glutInitDisplayMode( GLUT_SINGLE | GLUT_RGB );
glutInitWindowPosition( 50, 50 );
glutInitWindowSize( 200, 200 );
glutCreateWindow( "Hello World" );
glutDisplayFunc( display );
glutMainLoop( );
return 0;
}
Functions
void glutInit() to initialize the GLUT library, the variables should be the same in main()
void glutInitDisplayMode(),
void glutInitWindowsSize(),
void glutWindowPosition() define the type of window, its size, and its position (detail in OpenGL Utility ToolKit)
int glutCreateWindow(“Hello World”) creates a window on the screen with the given title. This function returns an integer that can be used to refer to the window in multiwindow environments
void glutMainLoop() causes the program to enter an event-processing loop. Should be in the end in the main function
Display Function
void display( )
{
// Clear the background before drawing
glClear( GL_COLOR_BUFFER_BIT );
// Actual code to do the drawing
glBegin( GL_POLYGON );
glVertex2f( -0.5, -0.5);
glVertex2f( -0.5, 0.5);
glVertex2f( 0.5, 0.5);
glVertex2f( 0.5, -0.5);
glEnd();
// Ensure all drawing commands are executed
glFlush( );
}
Procedure to draw a rectangle
Clearing the window glClear(GL_COLOR_BUFFER_BIT);
Drawing the rectangle Must starts with glBegin and ends with glEnd. Drawing the rectangle must be in between them
Flushing GL buffers Force to render or display the rectangle on the windows using glFlush functions
glFlush();
What is entity, geometry and attributes
Entity: lines, polygon, triangle
Geometry: coordinates of the vertices
Attribute: color, thickness
Data Types
character C-language type OpenGL type definition b signed char GLbyte
s short GLshort
i int GLint, GLsizei
f float GLfloat, GLclampf
d double GLdouble, GLclampd
ub unsigned char GLubyte, GLboolean
us unsigned short GLushort
ui unsigned int GLuint, GLenum, GLbitfield
void GLvoid
Coordinate System in OpenGL
void glVertex{234}{sifd}(TYPE x, TYPE y, …)
void glVertex{234}{sifd}v(TYPE *v)specifies the location in space of the vertex with type of coordinate.
If v presence, the coordinate must be declared as arrayglVertex2f(2.0, 2.0);
glVertex2fv(p); // p[0] = 2.0, p[1] = 2.0The 4th coord is homogenous specifically used during transformation
CS in OpenGL and Window
glutinitwindowside() sets the windows size in pixels.
CS in OpenGL is according to Cartesian CS in plane XY. By default the origin is in the center of the window and bottom left is (-1,-1) and top right is (1,1).
200 x 200 pixel and 500 x 500 pixel will have the same bottom left (-1,-1) and top right (1,1)
gluOrtho2D sets the new bottom left and top right point.
gluOrtho2D(GLdouble minx, GLdouble maxx , GLdouble miny, GLdouble maxy) will set the new clipping area. This is place after glutDisplayFunc() function
glutDisplayFunc( display );
gluOrtho2D(-2.0, 2.0, -2.0, 2.0);
Color in OpenGL
void glColor3{bsifd ubusui}{v} (TYPE r, TYPE g, TYPE b);
void glColor4{bsifd ubusui}{v} (TYPE r, TYPE g, TYPE b, TYPE a);a is alpha, to measure opacity; 1.0 is opaque and 0.0 is
transparent
(1.0, 1.0, 1.0): white
(1.0, 0.0, 0.0): bright red
Coloring the polygon
glColor3f(1.0,1.0,0.0);// Actual code to do the drawing
glBegin( GL_POLYGON );
glVertex2f( -0.5, -0.5);
glVertex2f( -0.5, 0.5);
glVertex2f( 0.5, 0.5);
glVertex2f( 0.5, -0.5);
glEnd();
glBegin( GL_POLYGON );
glColor3f(1.0,1.0,1.0);glVertex2f( -0.5, -0.5);
glColor3f(1.0,0.0,0.0);glVertex2f( -0.5, 0.5);
glColor3f(0.0,1.0,0.0);glVertex2f( 0.5, 0.5);
glColor3f(0.0,0.0,1.0);glVertex2f( 0.5, -0.5);
glEnd();
Thickness Attribute
Point: the size of the pointvoid glPointSize(GLfloat pixel_size )
glPoint Size( 5.0);
*this function must be before glBegin
Line: the width of the linevoid glLineWidth(GLfloat pixel_width)
glLineWidth( 5.0);
Primitive Points and Lines
Filled Primitives
Window related functions
void glutDestroyWindow(int id)Destroys top-level window id
void glutSetWindow(int id)Set the current to the window with identifier id
int glutCreateSubWindow(int parent, int x, int y,int width, int height)Create subwindows to specified id windows
void glutPostWindowRedisplay(int winid)Post a redisplay for window winid
Example
Circle can be drawn using connected lines. The lines
are drawn using the following formula
x = r cos (θ) y = r sin (θ)As the angle gets smaller, the connected lines will
form a circle. Therefore, the task is to draw a circle
using this angle θ = 10o.
