第一次實驗：理解語句

#include<GL/glut.h>
#include<math.h>
int i;
const int n=1000;
const GLfloat R=0.5f;
const GLfloat Pi=3.1415926536f;
void myDisplay(void)
{
	glClearColor(0.0,0.0,0.0,0.0);
	glClear(GL_COLOR_BUFFER_BIT);
        //畫正方形
	glColor3f(1.0f,1.0f,1.0f);
	glRectf(-0.5f,-0.5f,0.5f,0.5f);

        // 畫三角形
	glBegin(GL_TRIANGLES);//glBegin()和glEnd()函式之間呼叫函式完成點、線、和多邊形的繪製。</span>
	glColor3f(1.0f,0.0f,0.0f);glVertex2f(0.0f,1.0f);
	glColor3f(0.0f,1.0f,0.0f);glVertex2f(0.8f,-0.5f);
	glColor3f(0.0f,0.0f,1.0f);glVertex2f(-0.8f,-0.5f);
	glEnd();
       //圓
   glColor3f(1.0f, 0.0f, 1.0f);
   glBegin(GL_POLYGON);
   for(i=0; i<n; ++i)
        glVertex2f(R*cos(2*Pi/n*i), R*sin(2*Pi/n*i));
    glEnd();

    //五角星
   glColor3f (0.0f, 0.0f, 1.0f);
   GLfloat a = 1 / (2-2*cos(72*Pi/180));
   GLfloat bx = a * cos(18 * Pi/180);
   GLfloat by = a * sin(18 * Pi/180);
   GLfloat cy = -a * cos(18 * Pi/180);
   GLfloat
        PointA[2] = { 0, a },      PointB[2] = { bx, by },
        PointC[2] = { 0.5, cy },   PointD[2] = { -0.5, cy },
        PointE[2] = { -bx, by };  
    glBegin(GL_LINE_LOOP);
    glVertex2fv(PointA);    glVertex2fv(PointC);
    glVertex2fv(PointE);    glVertex2fv(PointB);
    glVertex2fv(PointD);
    glEnd();

    //點
	glPointSize(3);
	glBegin(GL_POINTS);
	glColor3f(1.0f,0.0f,0.0f);glVertex2f(-0.6f,0.6f);
	glColor3f(0.0f,1.0f,0.0f);glVertex2f(0.6f,-0.0f);
	glColor3f(0.0f,0.0f,1.0f);glVertex2f(-0.6f,-0.6f);
	glEnd();

	glFlush();//函式啟動OpenGL繪圖命令的執行，並將圖形光柵化後輸出在裝置上。</span>
}

int main(int argc,char *argv[])//注意
{
    glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_RGB|GLUT_SINGLE);
	glutInitWindowPosition(100,100);
	glutInitWindowSize(400,400);
	glutCreateWindow("Hello world!");
	glutDisplayFunc(&myDisplay);
	glutMainLoop();
	return 0;
}
 

執行結果: