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Displays and OpenGL (slides adapted from Amitabh Varshney)

Displays and OpenGL (slides adapted from Amitabh Varshney). Displays. Pixels Color Single vs. double buffers. Human Visual System. Image removed. Image from Fig 1.1 Principles of Digital Image Synthesis by A. Glassner. Human Visual System. Rods (intensity) 120 million

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Displays and OpenGL (slides adapted from Amitabh Varshney)

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  1. Displays and OpenGL(slides adapted from Amitabh Varshney)

  2. Displays • Pixels • Color • Single vs. double buffers

  3. Human Visual System Image removed Image from Fig 1.1 Principles of Digital Image Synthesis by A. Glassner

  4. Human Visual System • Rods (intensity) 120 million • Cones (color) 6 million • Three kinds of cones RGB • Fovea 1 to 2 degrees • 147K cones/mm Image removed Image from Fig 3.4 Spatial Vision by DeValois and DeValois

  5. Color • Displays with three colors • RGB representation of color • Red (1,0,0); Green (0,1,0); blue (0,0,1) • White (1,1,1); black (0,0,0) • Pink? Purple?

  6. OpenGL • State machine: implicit global variables • The window, where it is, size, etc…. • The current color for drawing. • Buffers • Type of projection • Interactive programming: callbacks • Don’t think about executing a program. Think about setting up functions that the user’s actions will call.

  7. Callbacks • glutDisplayFunc – gets called when screen display needed. • glutMouseFunc – called when mouse action occurs. • glutKeyboardFunc

  8. Getting Started • Conventions • OpenGL functions begin gl, each word in caps: eg., glBegin, glPolygonMode • Constants: GL_2D, GL_RGB, … • Data types: GLbyte, GLfloat, …

  9. GLUT • OpenGL machine independent • GLUT machine dependent • Display • Input devices • GLUT functions: glutInitWindowSize, glutIdleFunc, … • GLUT constants: GLUT_RIGHT_BUTTON, …

  10. Initialization • #include <GL/glut.h> • Also includes windows stuff and OpenGL • glutInit (int * argcp, char **argv) • Initialize GLUT library, parse and use command-line options: • glutInitWindowSize (int width, int height) • glutInitWindowPosition (int x, int y) • glutInitDisplayMode (unsigned int mode) • GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE, etc… • Single argument with OR of constants • Type of buffering, we’ll use single at first. • glutCreateWindow (char *window_name)

  11. Initializing window • glutInitWindowPosition (350, 100); • Where to put the window. • glutInitWindowSize (winWid, winHght); • And its size • glutCreateWindow (“Triangle Program"); • glClearColor (1.0, 1.0, 1.0, 0.0) • Background properties • First three give RGB values • Fourth gives blending for transparent objects. We won’t use this for a while.

  12. Projection • glMatrixMode (GL_PROJECTION); • The current matrix relates to projection. We won’t use others right now. • gluOrtho2D (0.0, winWth, 0.0,winHght); • Sets up orthographic projection from 3D scene to image. More on this later. • This form sets up most trivial projection.

  13. GLUT Callback Registration • glutDisplayFunc (void (*func) (void)) • glutReshapeFunc (void (*func) (int width, int height)) • glutKeyboardFunc(void (*func) (unsigned char key, int x, int y)) • Mouse position (x, y) when key was pressed • glutMouseFunc (void (*func) (int button, int state, int x, int y)) • Button: GLUT_LEFT_BUTTON, GLUT_MIDDLE_BUTTON, GLUT_RIGHT_BUTTON • State: GLUT_UP , GLUT_DOWN • Position (x, y): window relative coordinates

  14. GLUT Callback Registration • glutMotionFunc (void (*func) (int x, int y)) • Mouse motion while pressed • glutPassiveMotionFunc (void (*func) (int width, int height)) • Mouse motion without button press • glutIdleFunc(void (*func) (void)) • Called whenever no other events are on the event queue • Passing NULL disables this • glutTimerFunc (unsigned int msecs, void (*func) (int value), value)) • Callback every msecs milliseconds (or more): Best effort • Function func called with the specified value parameter • Can register multiple timer functions

  15. GLUT Main Event Loop • glutMainLoop (void) • Starts the GLUT even processing loop • Never returns • Calls registered function callbacks (user-defined event handlers) as appropriate • Should be called at most once

  16. Specifying Vertices • glVertex2s(200, -150); • 2D point in short coordinates • glVertex3i(200, -150, 40); • 3D point in integer coordinates • GLdouble dpoint[3] = {200.0, -150.5, 40.0}; glVertex3dv (dpoint);

  17. Points, Lines, Polygons • glBegin(mode) and glEnd( )delimit an object • mode can be one of the following: • GL_POINTS • GL_LINES • GL_POLYGON • GL_LINE_STRIP • GL_TRIANGLE_STRIP • GL_TRIANGLES • GL_QUADS • GL_LINE_LOOP • GL_QUAD_STRIP • GL_TRIANGLE_FAN

  18. Points glBegin(GL_POINTS); glVertex2i( 0, 0 ); glVertex2i( 0, 1 ); glVertex2i( 1, 0 ); glVertex2i( 1, 1); glEnd( );

  19. Line Loop (Polyline) glBegin(GL_LINE_LOOP); glVertex2i( 0, 0 ); glVertex2i( 0, 1 ); glVertex2i( 1, 1 ); glVertex2i( 1, 0 ); glEnd( );

  20. Polygon glBegin(GL_POLYGON); glVertex2i( 0, 0 ); glVertex2i( 0, 1 ); glVertex2i( 1, 1 ); glVertex2i( 1, 0 ); glEnd( );

  21. Triangles glBegin(GL_TRIANGLES); glVertex2i( 0, 0 ); // a glVertex2i( 0, 1 ); // b glVertex2i( 1, 0 ); // c glVertex2i( 0, 1 ); // b glVertex2i( 1, 0 ); // c glVertex2i( 1, 1 ); // d glVertex2i( 1, 0 ); // c glVertex2i( 1, 1 ); // d glVertex2i( 2, 0 ); // e glEnd( ); b d a c e

  22. Triangle Strip glBegin(GL_TRIANGLE_STRIP); glVertex2i( 0, 0 ); // a glVertex2i( 0, 1 ); // b glVertex2i( 1, 0 ); // c glVertex2i( 1, 1 ); // d glVertex2i( 2, 0 ); // e glEnd( ); b d a c e

  23. Attributes • Point • Point size:glPointSize(2.0); • Point color: glColor3f (0.0, 0.0, 1.0); • Line • Line width:glLineWidth(2.0); • Line color: glColor3f (0.0, 0.0, 1.0); • Face • Front and/or back: GL_FRONT, GL_BACK, GL_FRONT_AND_BACK • Face color: glColor3f (0.0, 0.0, 1.0);

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