计算机图形学（二）输出图元_20_章节总结_程序展示_折线图和直方图

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折线图和直方图

第一个程序展示使用一条折线、一组多点标记和位图字符标号来生成一年内按月的折线图。尽管等宽字体与图中的位置比较容易对齐，但此处给出了比例空间的字体。由于位图左下角提供了当前光栅位置的参考，所以我们必须移动参考位置以使文字串中心与绘制数据的位置对齐。图3.67给出了折线图程序的输出。

#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 ( );}

第二个程序使用同样的数据集生成图3.68所示的直方图。该程序展示了矩形填充区及位图字符标号的应用。

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 ( );}

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