折線圖和直方圖

       第一個程式展示使用一條折線、一組多點標記和點陣圖字元標號來生成一年內按月的折線圖。儘管等寬字型與圖中的位置比較容易對齊，但此處給出了比例空間的字型。由於點陣圖左下角提供了當前光柵位置的參考，所以我們必須移動參考位置以使文字串中心與繪製資料的位置對齊。圖3.67給出了折線圖程式的輸出。

#include <GL/glut.h>


GLsizei winWidth = 600, winHeight = 500;  //Initial display window size.
GLint xRaster = 25, yRaster = 150;        // Initialize raster position.


GLubyte label [36] = { 'J', 'a', 'n',  'F', 'e', 'b',  'M', 'a', 'r',
                       'A', 'p', 'r',  'M', 'a', 'y',  'J', 'u', 'n',
					   'J', 'u', 'l',  'A', 'u', 'g',  'S', 'e', 'p',
					   'O', 'c', 't',  'N', 'o', 'v',  'D', 'e', 'c'};


GLint dataValues [12] = {420, 342, 324, 310, 262, 185,
                        190, 196, 217, 240, 312, 438};
						
void init (void)
{
    glClearColor (1.0, 1.0, 1.0, 1.0);  //White display window.
    glMatrixMode (GL_PROJECTION);
	gluOrtho2D (0.0, 600.0, 0.0, 500.0);
}


void lineGraph (void)
{
    GLint month, k;  
	GLint x = 30;                    // Initialize x position for chart.
	glClear (GL_COLOR_BUFFER_BIT);   // Clear display window.
	glColor3f (0.0, 0.0, 1.0);       // Set line color to blue.
	glBegin (GL_LINE_STRIP);         // Plot data as a polyline.
	    for (k = 0; k < 12; k++)
		    glVertex2i (x + k * 50, dataValues [k]);
	glEnd ();
	
	glColor3f (1.0, 0.0, 0.0);       // Set marker color to red.
	for (k = 0; k < 12; k++){        // Plot data as asterisk polymarkers.
	    glRasterPos2i (xRaster + k * 50, dataValues [k] - 4);
		glutBitmapCharacter (GLUT_BITMAP_9_BY_15, '*');
	}
	
	glColor3f (0.0, 0.0, 0.0);       // Set test color to black.
	xRaster = 20;                    // Display chart labels.
	for (month = 0; month < 12; month++) {
	    glRasterPos2i (xRaster, yRaster);
		for (k = 3 * month; k < 3 * month + 3; k++)
		    glutBitmapCharacter (GLUT_BITMAP_HELVETICA_12, label [k]);
		xRaster += 50;
	}
	glFlush ( );
}


void winReshpeFcn (GLint newWidth, GLint newHeight)
{
    glMatrixMode (GL_PROJECTION);
	glLoadIdetity ( );
	gluOrtho2D (0.0, GLdouble (newWidth), 0.0, GLdouble (newHeight));
	glClear (GL_COLOR_BUFFER_BIT);


}


void main (int argc, char** argv)
{
    glutInit (&argc, argv);
	glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
	glutInitWindowPosition (100, 100);
	glutInitWindowSize (winWidth, winHeight);
	glutCreateWindow ("Line Chart Data Plot");
	
	init ( );
	glutDisplayFunc (lineGraph);
	glutReshapeFunc (winReshpeFcn);
	
	glutMainLoop ( );
}
 

第二個程式使用同樣的資料集生成圖3.68所示的直方圖。該程式展示了矩形填充區及點陣圖字元標號的應用。

void barChart (void)
{
    GLint month, k;
	glClear (GL_COLOR_BUFFER_BIT); // Clear display window.
	glColor3f (1.0, 0.0, 0.0);     // Set bar color to red.
	for (k = 0, k < 12; k++)
	    glRecti (20 + k * 50, 165, 40 + k * 50, dataValues [k]);
	glColor3f (0.0, 0.0, 0.0);     // Set text color to black.
	xRaster = 20;                  // Display chart labels.
	for (month = 0; month < 12; month++){
	    glRasterPos2i (xRaster, yRaster);
		for (k = 3 * month; k < 3 * month + 3; k++)
		    glutBitmapCharacter (GLUT_BITMAP_HELVETICA_12, label [h]);   
		xRaster += 50;
	}
	glFlush ( );


}