[OpenGL]課後案例05：產生正方形的程式

//A.5  產生正方形的程式/* This program illustrates the use of the GLUT library forinterfacing with a Window System *//* The program opens a window, clears it to black,then draws a box at the location of the mouse each time theleft button is clicked. The right button exits the program.The program also reacts correctly when the window ismoved or resized by clearing the new window to black.  */#include <GL/glut.h>#include <stdlib.h>/* globals */GLsizei wh = 500, ww = 500; /* initial window size */GLfloat size = 3.0;   /* half side length of square */void drawSquare(int x, int y){    y=wh-y;    glColor3ub( (char) rand()%256, (char) rand()%256, (char) rand()        %256);    glBegin(GL_POLYGON);    glVertex2f(x+size, y+size);    glVertex2f(x-size, y+size);    glVertex2f(x-size, y-size);    glVertex2f(x+size, y-size);    glEnd();    glFlush();}/* reshaping routine called whenever window is resizedor moved */void myReshape(GLsizei w, GLsizei h){    /* adjust clipping box */    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    glOrtho(0.0, (GLdouble)w, 0.0, (GLdouble)h, -1.0, 1.0);    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();    /* adjust viewport and clear */    glViewport(0,0,w,h);    glClear(GL_COLOR_BUFFER_BIT);    glFlush();    /* set global size for use by drawing routine */    ww = w;    wh = h;}void myinit(void){    glViewport(0,0,ww,wh);    /* Pick 2D clipping window to match size of screen window.    This choice avoids having to scale object coordinates    each time window is resized. */    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    glOrtho(0.0, (GLdouble) ww, 0.0, (GLdouble) wh, -1.0, 1.0);    /* set clear color to black and clear window */    glClearColor (0.0, 0.0, 0.0, 1.0);    glClear(GL_COLOR_BUFFER_BIT);    glFlush();}void mouse(int btn,int state,int x,int y){    if(btn==GLUT_RIGHT_BUTTON &&state==GLUT_DOWN)  exit(0);}/* display callback required by GLUT*/void display(){}int main(int argc,char** argv){    glutInit(&argc,argv);    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);    glutCreateWindow("square");    myinit();    glutReshapeFunc (myReshape);    glutMouseFunc (mouse);    glutMotionFunc (drawSquare);    glutDisplayFunc (display);    glutMainLoop();}