OpenGL实现2D正方形公转和自转

1.实验一（改进后使用glTranslate函数）

公转截图1

公转截图2

#include "pch.h"
#include 
#include 
#define Rwidth 0.15
#define Rheight 0.15
#define n 360
#define DEG_TO_RAD 0.017453
GLfloat theta = 0.0;
GLfloat th = 0.0;
const GLfloat radius = 0.6;
const GLfloat Pi = 3.1415926536;
const GLfloat ac = 0.1;   
void init() {
    glClearColor(1.0, 1.0, 1.0, 1.0);
}
void displayFcn()
{
    glClear(GL_COLOR_BUFFER_BIT);       //clear the window

    glBegin(GL_LINE_LOOP);          //draw a circle
    for (GLint i = 0; i < n; i++) {
        glColor3f(0.0, 0.0, 0.0);
        glVertex2f(radius *cos(2 * Pi / n * i), radius * sin(2 * Pi / n * i));
    }
    glEnd();

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef(-radius * cos(th * DEG_TO_RAD), - radius * sin(th * DEG_TO_RAD), 0.0);     //the rectanguler's translation
    glBegin(GL_POLYGON);                        // Rotation
    glVertex2f(-Rwidth / 2, -Rheight / 2 );
    glVertex2f(Rwidth / 2 , -Rheight / 2 );
    glVertex2f(Rwidth / 2 , Rheight / 2);
    glVertex2f(-Rwidth / 2 , Rheight / 2);
    glEnd();

    glFlush();
}
void rotate()
{
    th += 0.1;
    if (th > 360.0)
        th -= 360.0;
    glutPostRedisplay();
}
int main(int argc, char *argv[])
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
    glutInitWindowPosition(100, 100);
    glutInitWindowSize(800, 1000);
    glutCreateWindow("rect");
    glutDisplayFunc(displayFcn);
    init();
    glutIdleFunc(rotate);
    glutMainLoop();
    return 0;
}

2.实验二（只使用了glRotare）

截图1

截图2

#include "pch.h"
#include 
#include 
#define Rwidth 0.2
#define Rheight 0.15
#define n 360
#define DEG_TO_RAD 0.017453
GLfloat theta = 0.0;
GLfloat th = 0.0;
const GLfloat radius = 0.6;
const GLfloat Pi = 3.1415926536;
const GLfloat ac = 0.1;
void init() {
    glClearColor(1.0, 1.0, 1.0, 1.0);
}
void displayFcn()
{
    glClear(GL_COLOR_BUFFER_BIT);       //clear the window

    glBegin(GL_LINE_LOOP);          //draw a circle
    for (GLint i = 0; i < n; i++) {
        glColor3f(0.0, 0.0, 0.0);
        glVertex2f(radius *cos(2 * Pi / n * i), radius * sin(2 * Pi / n * i));
    }
    glEnd();

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef(-radius * cos(th * DEG_TO_RAD), -radius * sin(th * DEG_TO_RAD), 0.0);
    glRotatef(theta *4, 0.0, 0.0, 1);    //4:1
    glBegin(GL_POLYGON);            
    glVertex2f(-Rwidth / 2, -Rheight / 2);
    glVertex2f(Rwidth / 2, -Rheight / 2);
    glVertex2f(Rwidth / 2, Rheight / 2);
    glVertex2f(-Rwidth / 2, Rheight / 2);
    glEnd();

    glFlush();
}
void rotate()
{
    theta += 0.18;
    if (theta > 360.0)
        theta -= 360.0;

    th += 0.18;
    if (th > 360.0)
        th -= 360.0;
    glutPostRedisplay();
}
int main(int argc, char *argv[])
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
    glutInitWindowPosition(100, 100);
    glutInitWindowSize(800, 1000);
    glutCreateWindow("rect");
    glutDisplayFunc(displayFcn);
    init();
    glutIdleFunc(rotate);
    glutMainLoop();
    return 0;
}

注：注意在实验二中，glTranslatef()和glRotatef()是理解这个实验的关键。