OpenGL (Graphics Library) Software Interface to graphics software Allows to create interactive programs that produce color images of moving 3D objects.
OpenGL ● OpenGL – Hardware independent, only specifies graphics output low level, no GUI operations (events, windows, menu’s) ●OpenGL Utility (GLU) – Higher level graphics primitives (spheres, curves, curved surfaces) ●OpenGL Utility Toolkit (GLUT) – Primitive window setup & event handling. enables truly window system independent applications
OpenGL Basic Syntax (C Language Binding) ●Functions: glXXXX – glBegin, glEnd, glPolygonMode ●Constants: GL_XXXX – GL_2D, GL_RGB, GL_CCW ●Types: GLxxx – GLbyte, GLshort, GLint, GLfloat, GLdouble, GLboolean
OpenGL Header Files #include However, If using GLUT to handle window- managing operations #include
Display-Window Management Using GLUT Step1 : GLUT Initialization glut Init (&argc, argv); Step2 : Display window is created on the screen with the function glutCreateWindow ( “ An Example OpenGL Program”); Other functions such as : glutDisplayFunc ( lineSegment); //displaying any object glutInitWindowPosition (50, 100); // set the position of window
Display-Window Management Using GLUT.. glutInitWindowSize (400, 300); //set the size of the window glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB); //options for buffering and color modes Final Step : All display windows are activated and displayed glutMainLoop ( ); This function completes the window- processing operations.
OpenGL Program Example #include void init (void) { glClearColor (1.0, 1.0, 1.0, 0.0); //Set Display-window color to white glMatrixMode (GL_PROJECTION); // Set projection parameters gluOrtho2D (0.0, 200.0, 0.0, 150.0); }
Continued.. void lineSegment (void) { glClear (GL_COLOR_BUFFER_BIT); // Clear display window glColor3f (1.0, 0.0, 0.0); //Set line segment color to red glBegin (GL_LINES); glVertex2i (180, 15); //Specify line- segment geometry glVertex2i (10, 145); glEnd (); glFlush (); // Process all OpenGL routines as quickly as possible }
Continued.. void main (int argc, char** argv) { glutInit (&argc, argv);// Initialize GLUT glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB); // Set display mode glutInitWindowPosition (50, 100); //Set top-left display-window position glutInitWindowSize (400,300); //Set display-window width and height
Continued.. glutCreateWindow ("An Example OpenGL Program");// Create display window init (); // Execute initialization procedure glutDisplayFunc (lineSegment); // Send graphics to display window glutMainLoop (); }
OpenGL Geometric Output Primitives ●Types: GL_POINTS, GL_LINES, GL_LINE_LOOP, GL_LINE_STRIP, GL_POLYGON, GL_QUADS, GL_QUAD_STRIP, GL_TRIANGLE, GL_TRIANGLE_STRIP, GL_TRIANGLE_FAN ●Basic Syntax: glBegin (PrimitiveConstant); glVertex3f (x1,y1,z1) glVertex3f (x2,y2,z2) …. glEnd(); glVertex(2|3|4)(s|i|d|f)[v]
Points & Lines v0 v1 v2 v3 glBegin (PrimitiveConstant); glVertex3f (x1,y1,z1) glVertex3f (x2,y2,z2) …. glEnd(); v0 v1 v2 v3 v4 v5 GL_POINTS GL_LINES GL_LINE_STRIP v0 v1 v2 v3 v4 GL_LINE_LOOP
Polygons glBegin (PrimitiveConstant); glVertex3f (x1,y1,z1) glVertex3f (x2,y2,z2) …. glEnd(); GL_POLYGON v0 v1 v2 v3 v4 v0 v1 v2 v3 v4 v5 v6 v7 GL_QUADS v0 v1 v2 v3 v4 v5 v6 v7 GL_QUAD_STRIP
Polygons (2) glBegin (PrimitiveConstant); glVertex3f (x1,y1,z1) glVertex3f (x2,y2,z2) …. glEnd(); v0 v1 v2 v3 v4 v5 GL_TRIANGLES GL_TRIANGLE_STRIP v0 v1 v2 v3 v4 v5 GL_TRIANGLE_FAN v0 v1 v2 v3 v4 v5 N vertices N/3 Triangles N+2 vertices N Triangles N+2 vertices N Triangles
References Computer Graphics with OpenGL :H & B RedBook : Tutorials : ITCS 4120 class notes