Exploring OpenGL Arrays and Display Lists

1. Chapter 3 arrays of vertices vertex arrays display lists drawing text mouse buttons

2. Arrays of vertices (and colors)squareAnnulus2.cpp • vertices and colors in global arrays • vertices accessed through pointers glVertex3fv(pointer to vertex) • colors accessed through pointers glColor3fv(pointer to color) • Look at the code.

3. Accessing an Array of Vertices with pointers // Draw square annulus. glBegin(GL_TRIANGLE_STRIP); for(int i = 0; i < 10; ++i) { glColor3fv(colors[i%8]); glVertex3fv(vertices[i%8]); } glEnd();

4. ARRAY OF VERTICES vsVERTEX ARRAY ARRAY OF VERTICES // Vertex co-ordinate vectors. static float vertices[8][3] = { {30.0, 30.0, 0.0}, {10.0, 10.0, 0.0}, {70.0, 30.0, 0.0}, {90.0, 10.0, 0.0}, {70.0, 70.0, 0.0}, {90.0, 90.0, 0.0}, {30.0, 70.0, 0.0}, {10.0, 90.0, 0.0} }; VERTEX ARRAY // Vertex co-ordinate vectors. static float vertices[] = { 30.0, 30.0, 0.0, 10.0, 10.0, 0.0, 70.0, 30.0, 0.0, 90.0, 10.0, 0.0, 70.0, 70.0, 0.0, 90.0, 90.0, 0.0, 30.0, 70.0, 0.0, 10.0, 90.0, 0.0 };

5. roomStripe.cpp • Room is built with a list of vertices • Figure out where the room is in world coords. • Decide where you want the stripe to be, get 14 points • Stripe is drawn using a Vertex Array.

6. roomStripe.cpp • Color can be solid or use a Color Array • Need to set up and enable these arrays. • Discuss input from a file in C++ • Discuss changing Frustum/Ortho

7. Vertex ArrayssquareAnnulus3.cpp • vertices in one dimensional vertex array • colors in one dimensional color array • vertex and color are accessed together glArrayElement(i%8); glArrayElement(location of vertex); Need info to know where that is!

8. To use vertex arrays you need to • say you are using a vertex array and a color array. glEnableClientState(GL_VERTEX_ARRAY); glEnableClientState(GL_COLOR_ARRAY); • say where to find the data glVertexPointer(3, GL_FLOAT, 0, vertices); glColorPointer(3, GL_FLOAT, 0, colors); (size, type, stride, *pointer) • Look at code. (squareAnnulus3.cpp or roomStripe.cpp)

9. squareAnnulus4.cpp • In addition to vertex and color arrays (1D) there is an index array staticunsignedchar stripIndices[] = {0, 1, 2, 3, 4, 5, 6, 7, 0, 1}; • One draw statement glDrawElements(GL_TRIANGLE_STRIP, 10, GL_UNSIGNED_BYTE, stripIndices); (primitive, count, type, *indices) • Look at code.

10. OpenGL redefines types.Use GL types as parameters to GL functions. Sometimes you will need to declare the item using the GL type, eg.GLfloat length;

11. Display Lists • compiled once • can save to machine running the display • can be invoked by a single command • Uses the values of variables at the time it compiles, not at the time it is displayed.

12. helixList.cpp // Globals. staticunsignedint aHelix; // List index. in setup(): aHelix = glGenLists(1); // Return a list index. // Begin create a display list. glNewList(aHelix, GL_COMPILE); // Draw a helix. glBegin(GL_LINE_STRIP); for(t = -10 * PI; t <= 10 * PI; t += PI/20.0) glVertex3f(20 * cos(t), 20 * sin(t), t); glEnd(); glEndList(); // End create a display list.

13. helixList.cpp in drawScene(): glCallList(aHelix); // Execute display list.

14. see the text for a discussion of executing multiple display lists with one call.

15. Drawing Text - Bitmap • Need to go to the right pixel: glRasterPos3f(p,q,r);//object coordinates • call a function to draw the string, like writeBitmapString(font, string) // Routine to draw a bitmap character string. void writeBitmapString(void *font, const char *string) { const char *c; for (c = string; *c != '\0'; c++) glutBitmapCharacter(font, *c); } • use a glut function for drawing a char • glutBitmapCharacter(font, *c);

16. Sample Letters

17. Available Bitmap Fonts GLUT_BITMAP_8_BY_13 GLUT_BITMAP_9_BY_15 GLUT_BITMAP_TIMES_ROMAN_10 GLUT_BITMAP_TIMES_ROMAN_24 GLUT_BITMAP_HELVETICA_10 GLUT_BITMAP_HELVETICA_12 GLUT_BITMAP_HELVETICA_18

18. See CircularAnuluses.c for an example

19. Drawing Text - Stroke • Works like drawing lines. Uses color, linewidth,... • Assumes at the origin, use glTranslate to move to the right spot, glScale to make the right size

20. Available Stroke Fonts GLUT_STROKE_ROMAN GLUT_STROKE_MONO_ROMAN Run fonts.cpp

21. Stroke text cont. • Use the canonical function // Routine to draw a stroke character string. void writeStrokeString(void *font, const char *string) { constchar *c; for (c = string; *c != '\0'; c++) glutStrokeCharacter(font, *c); } • Use a glut function to draw the char glutStrokeCharacter(font, *c);

22. Bitmaps don't scale. • Stroke scale, rotate.

23. Programming the mouse • clicking a button - register with glutMouseFunc(mouseButton) • dragging with a button down - register with glutMotionFunc(mouseMotion) • dragging with no button down - register with glutPassiveMotionFunc(mousePassive)

24. void mouseButton(int button, int state, int x, int y); button can be GLUT_LEFT_BUTTON GLUT_RIGHT_BUTTON GLUT_MIDDLE_BUTTON state can be GLUT_UP GLUT_DOWN

25. int x, int y (x,y) is the location in the OpenGL window, measured in pixels, with origin in the upper left corner.

26. mouse.cpp • Run. • Notice the use of STL vector. • Look at the mouse control function. • Look at the resize function, and the resize behavior.

27. STL vector Point is user defined type. vector<Point> points; // Iterator to traverse a Point array. vector<Point>::iterator pointsIterator; // Store the clicked point in the points array after correcting // from event to OpenGL co-ordinates. points.push_back( Point(x, height - y) );

28. drawing the points // Loop through the points array drawing each point. pointsIterator = points.begin(); while(pointsIterator != points.end() ) { pointsIterator->drawPoint(); pointsIterator++; }

29. mouseMotion.cppmodified point size and color for demo • point is created when button is pressed. • coordinates of point are modified as mouse is moved with the button down • point is added to the vector when button is released • currentPoint • Look at code.