![2.2 Drawing basic graphics primitives Drawing Figures void Sierpinski(void) { GLintPoint T[3]= {{10,10},{300,30},{200, 300}}; int index = random(3); // 0, 1, or 2 equally likely GLintPoint point = T[index]; // initial point drawDot(point.x, point.y); // draw initial point for(int i = 0; i < 9000; i++) // draw 1000 dots { index = random(3); point.x = (point.x + T[index].x) / 2; point.y = (point.y + T[index].y) / 2; drawDot(point.x,point.y); } glFlush(); }](https://image.slidesharecdn.com/lecturegraphicsch2-1227437732353961-8/85/Drawing-Figures-13-320.jpg)
Drawing Figures
- 1. Getting Started Drawing Figures (chapter 2, F.S. Hill) In this chapter… Writing programs to produce pictures Basics of Open GL Develop elementary graphics tools for drawing Control the program by Input Devices
- 2. 2.1 Getting started Environment: window, coordinate system, Drawing Figures
- 3. 2.1 Getting started 2.1.1 Device-independence and OpenGL API Libraries 2.1.2 Windows-based Programming Event-driven, event queue and callbacks Old style “ do this then do this…..” New style “do nothing until an event occurs, and then do the specified thing” Callback-function System-Independent (glut) Drawing Figures
- 4. 2.1 Getting started A skeleton of an event-driven program: #include <gl/Gl.h> #include <gl/glut.h> //<<<<<<<<<<<<<<<<<<<<<<<< main >>>>>>>>>>>>>>>>>>>>>> void main(int argc, char** argv) { // initialize // create screen window glutDisplayFunc (myDisplay); glutMouseFunc (myMouse); glutKeyboardFunc (myKeyboard); glutMainLoop(); // go into a perpetual loop } Drawing Figures
- 5. 2.1 Getting started 2.1.3 Opening a window for drawing (framework) #include <windows.h> #include <gl/Gl.h> #include <gl/glut.h> //<<<<<<<<<<<<<<<<<<<<<<<< main >>>>>>>>>>>>>>>>>>>>>> void main(int argc, char** argv) { glutInit(&argc, argv); // initialize the toolkit glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); // set display mode glutInitWindowSize(640,480); // set window size glutInitWindowPosition(100, 150); // set window position on //screen glutCreateWindow("my first attempt"); // open the screen window glutDisplayFunc(myDisplay); // register redraw function myInit(); glutMainLoop(); // go into a perpetual loop } Drawing Figures
- 6. 2.2 Drawing basic graphics primitives Line drawing primitives : glBegin, glEnd, vertices Example: glBegin (GL_POINTS); glVertex2i(100,50); glVertex2i(100,130); glVertex2i(150,130); glEnd(); GL_POINTS GL_LINES GL_POLYGONE OpenGL commands: glVertex2i (…), 2f, etc Drawing Figures
- 7. 2.2 Drawing basic graphics primitives OpenGL data types : Drawing Figures
- 8. 2.2 Drawing basic graphics primitives OpenGL state: current state variables. Size of point and line Back/Foreground Color glColor3f (red, green, blue) glClearcolor(red,green,blue) glClear (GL_COLOR_BUFFER_BIT) Establish coordinate system (gluOrtho2d(..)) Drawing Figures
- 9. 2.2 Drawing basic graphics primitives Drawing Figures #include <windows.h> // use as needed for your system #include <GL/Gl.h> #include <GL/glut.h> //<<<<<<<<<<<<<<<<<<<<<<< myInit >>>>>>>>>>>>>>>>>>>> void myInit(void) { glClearColor(1.0,1.0,1.0,0.0); // set white background color glColor3f(0.0f, 0.0f, 0.0f); // set the drawing color glPointSize(4.0); // a ‘dot’ is 4 by 4 pixels glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluOrtho2D(0.0, 640.0, 0.0, 480.0); } A Complete Program
- 10. 2.2 Drawing basic graphics primitives Drawing Figures //<<<<<<<<<<<<<<<<<<<<<<<< myDisplay >>>>>>>>>>>>>>>>> void myDisplay(void) { glClear(GL_COLOR_BUFFER_BIT); // clear the screen glBegin(GL_POINTS); glVertex2i(100, 50); // draw three points glVertex2i(100, 130); glVertex2i(150, 130); glEnd(); glFlush(); // send all output to display } A Complete Program (continue)
- 11. 2.2 Drawing basic graphics primitives Drawing Figures //<<<<<<<<<<<<<<<<<<<<<<<< main >>>>>>>>>>>>>>>>>>>>>> void main(int argc, char** argv) { glutInit(&argc, argv); // initialize the toolkit glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); // set display mode glutInitWindowSize(640,480); // set window size glutInitWindowPosition(100, 150); // set window position on screen glutCreateWindow("my first attempt"); // open the screen window glutDisplayFunc(myDisplay); // register redraw function myInit(); glutMainLoop(); // go into a perpetual loop } A Complete Program (continue)
- 12. 2.2 Drawing basic graphics primitives 2.2.1 Drawing dot constellations The Sierpinski Gasket Drawing Figures
- 13. 2.2 Drawing basic graphics primitives Drawing Figures void Sierpinski(void) { GLintPoint T[3]= {{10,10},{300,30},{200, 300}}; int index = random(3); // 0, 1, or 2 equally likely GLintPoint point = T[index]; // initial point drawDot(point.x, point.y); // draw initial point for(int i = 0; i < 9000; i++) // draw 1000 dots { index = random(3); point.x = (point.x + T[index].x) / 2; point.y = (point.y + T[index].y) / 2; drawDot(point.x,point.y); } glFlush(); }
- 14. 2.2 Drawing basic graphics primitives Drawing Figures class GLintPoint{ public: GLint x,y; }; int random(int m) { return rand()%m; } void drawDot(GLint x, GLint y) { glBegin(GL_POINTS); glVertex2i(x,y); glEnd(); }
- 15. 2.2 Drawing basic graphics primitives Simple dot plots
- 16. 2.2 Drawing basic graphics primitives Simple dot plots f(x) = e -x cos(2px) BASIC PROCESS glBegin(GL_POINTS); for(GLdouble x = 0; x < 4.0 ; x += 0.005) glVertex2d(x,f(x)); glEnd(); Scaling x sx = x * screenWidth / 4.0; AS sx = A x + B Scaling and shifting y sy = ( y + 1.0 ) * screenHeight / 2.0; AS sy = C y + D
- 17. 2.2 Drawing basic graphics primitives GLdouble A, B, C, D; A = screenWidth / 4.0; B = 0.0; C = D = screenHeight / 2.0; glBegin(GL_POINTS); for(GLdouble x = 0; x < 4.0 ; x += 0.005) { GLdouble func = exp(-x) * cos(2 * 3.14159265 * x); glVertex2d(A * x + B, C * func + D); } glEnd(); glFlush(); Simple dot plots
- 18. 2.2 Drawing basic graphics primitives Drawing Figures Plot a Function
- 19. Plot a Function (Continued) Drawing Figures
- 20. 2.3 Line Drawings glBegin (GL_LINES); glVertex2i(40, 100); glVertex2i(202, 96); // More than 2 vertices : paired glEnd(); glLineWidth(1.0) // default General function for line Void drawLineint(GLint x1,GLint y1, GLint x1,GLint y1) { glBegin (GL_LINES); glVertex2i(x1, y1); glVertex2i(x2, y2); glEnd(); } Drawing Figures
- 21. 2.3 Line Drawings 2.3.1 Drawing polylines and polygons Polyline: collection of joined line segments, specified by ordered list of points. GL_LINE_STRIP (open line segment) GL_LINE_LOOP (closed line segment – not fillable) GL_POLYGON (closed line segment – fillable) Drawing Figures
- 22. 2.3 Line Drawings Drawing figures by stored vertices from file void drawPolyLineFile(char * fileName) { fstream inStream; inStream.open(fileName, ios ::in); // open the file if(inStream.fail()) return; glClear(GL_COLOR_BUFFER_BIT); // clear the screen GLint numpolys, numLines, x ,y; inStream >> numpolys; // read the number of polylines for(int j = 0; j < numpolys; j++) // read each polyline { inStream >> numLines; glBegin(GL_LINE_STRIP); // draw the next polyline for (int i = 0; i < numLines; i++) { inStream >> x >> y; // read the next x, y pair glVertex2i(x, y); } glEnd(); } glFlush(); inStream.close(); } Drawing Figures
- 23. 2.3 Line Drawings Drawing a house void hardwiredHouse(void) { glBegin(GL_LINE_LOOP); glVertex2i(40, 40); // draw the shell of house glVertex2i(40, 90); glVertex2i(70, 120); glVertex2i(100, 90); glVertex2i(100, 40); glEnd(); glBegin(GL_LINE_STRIP); glVertex2i(50, 100); // draw the chimney glVertex2i(50, 120); glVertex2i(60, 120); glVertex2i(60, 110); glEnd(); // draw the door // draw the window } Drawing Figures
- 24. 2.3 Line Drawings Parameterizing figures, polyline drawer void parameterizedHouse(GLintPoint peak, GLint width, GLint height) // the top of house is at the peak; the size of house is given // by height and width { glBegin(GL_LINE_LOOP); // draw shell of house glVertex2i(peak.x, peak.y); //draw left roof glVertex2i(peak.x + width / 2, peak.y - 3 * height /8); glVertex2i(peak.x + width / 2, peak.y - height); // left wall glVertex2i(peak.x - width / 2, peak.y - height); // bottom glVertex2i(peak.x - width / 2, peak.y - 3 * height /8); // right wall glEnd(); //draw chimney in the same fashion //draw the door //draw the window } Drawing Figures
- 25. 2.3 Line Drawings 2.3.2 Line drawing with moveto() and lineto() GLintPoint CP; // global current position //<<<<<<<<<<<<< moveto >>>>>>>>>>>>>> void moveto(GLint x, GLint y) { CP.x = x; CP.y = y; // update the CP } //<<<<<<<<<<<< lineTo >>>>>>>>>>>>>>>>> void lineto(GLint x, GLint y) { glBegin(GL_LINES); // draw the line glVertex2i(CP.x, CP.y); glVertex2i(x, y); glEnd(); glFlush(); CP.x = x; CP.y = y; // update the CP } Drawing Figures
- 26. 2.3 Line Drawings 2.3.3 Drawing aligned rectangles glRecti(x1,y1,x2,y2)// (example programs) 2.3.4 Aspect ratio of aligned rectangle width/height Drawing Figures
- 27. 2.3 Line Drawings 2.3.5 Filling polygons Must be convex! 2.3.6 Other graphics primitives: GL_TRIANGLES,GL_QUADS,GL_TRIANGLE_STRIP GL_TRIANGLE_FAN,GL_QUAD_STRIP Drawing Figures