CMP160

Spring 2007

Program # 1 FLTK/OpenGL Handout

Getting Started

In the first assignment we expect you to become familiar with basic 2D graphical objects under orthographic projection using OpenGL libraries and building interfaces with controls (widgets) using FLTK libraries. We are providing a sample template for the first assignment containing the following files.

prog1.cpp, prog1.h, gui.cpp, gui.h, graph.cpp, graph.h, Makefile

FLTK Basics

• For working on this assignment, familiarity with the second and third chapters from FLTK programming manual is sufficient.

• FLTK provides some common widgets like buttons, text, boxes, labels etc. The files gui.{cpp/h} take care of the fltk interface part. The sample template code contains only one exit button and a box for drawing the graph. FLTK interface changes should be made to the programs gui.cpp and gui.h. In addition to the box and the button, we need to place two more round buttons and a check button as shown in the output program.

• The round buttons are used to select bar graphs and line graphs. At a time only one round button should be enabled. We can set various properties like color, position, type, etc for each widget. For example by setting the type of the two round buttons to radio, we make sure that only one of them can be enabled at a time.

• A check button should be placed to view the ESI values near the graphs. On checking it, the values should be visible on the graph and vice versa.

• After creating these buttons, callback functions have to be written to handle the events on clicking the buttons. Playing around with other widgets for creative interfaces will be a very good learning experience.

OpenGL Basics

• Chapter 1 and first half of chapter 2 from the book OpenGL programming guide (red book) explain the necessary basics for implementing the first assignment. Some 2D graphical operations like clearing the screen, 2D orthographic projection and drawing basic geometric primitives like points, lines, filled polygons etc are required. The section on OpenGL Geometric Drawing Primitives from chapter 2 in the red book gives the necessary information for drawing various 2D objects.

• The drawing operations take place in the files graph.cpp and graph.h. For drawing the graphs you need to first load the ESI data for a city by reading a file in graph.cpp file. Then have two separate functions drawLineGraph() and drawBarGraph() for drawing line graphs and bar graphs respectively. The choice between line graph and bar graph is made based on the status of the corresponding round buttons. Also use a separate function for drawing the legends at one corner of the display box. If the legend is consistent with both the line graph and the bar graph then you don’t have to change it depending on the type of the graph.

• gluOrtho2D() function can be used for setting orthographic projection mode for viewing 2D objects. glClearColor( ) and glClear() functions can be used for clearing the screen before drawing the objects. For drawing points on a 2D screen we use glVertex2f() function. With the function calls glBegin(),glEnd() and glVertex2f(), we can draw different kinds of geometric primitives like points, lines, triangles, quads, polygons, etc by specifying the type of primitive. In our assignment we need to use this structure for drawing the line graph and bar graph for the temperature data. The line graph can be drawn using GL_LINE_STRIP primitive and the bar graph can be drawn using GL_QUADS primitive.

· By default all polygons are filled with the current color. In our program we need to set different colors for filling the bar graphs and legends.

• In addition to the given sample program, please spend some time on the sample programs in Chapter 2 of the red book for understanding various other OpenGL concepts like double buffering. You will need to modify only the files graph.cpp, graph.h, gui.cpp, gui.h and Makefile in this assignment. However you may add additional files for modularity.