OpenGL學習（二）——鍵盤輸入處理與三維對象運動

一 目標

    用線框繪製兩個球體，命名爲地球和月球。實現月球的自裝和公轉，並通過鍵盤輸入控制旋轉的方向

二 參考資料

1、glPushMatrix()和glPopMatrix()：https://blog.csdn.net/tyxkzzf/article/details/40907273

2、鍵盤控制：https://blog.csdn.net/xie_zi/article/details/1911891

三 源代碼

#include<GL\glut.h>
#include<math.h>

#define pi 3.1415926

//----------------//
// 觀察座標系參數 //
//----------------//

//觀察座標系原點
GLdouble x = 0.0;
GLdouble y = 2.0;
GLdouble z = 20.0;
//視點
GLdouble X = 0.0;
GLdouble Y = 0.0;
GLdouble Z = 0.0;
//向上向量
GLdouble vx = 0.0;
GLdouble vy = 1.0;
GLdouble vz = 0.0;

//---------------------------//
//    定義星球旋轉相關參數    //
//---------------------------//

GLint distance = 25; //星球間距離
GLdouble moonAngle = 0; //月球自轉角度
GLdouble revoAngle = 0; //公轉角度

//地球座標
GLdouble earthX = 0;
GLdouble earthY = 0;
GLdouble earthZ = 0;

//月球座標
GLdouble moonX = distance;
GLdouble moonY = 0;
GLdouble moonZ = 0;

//星球大小
GLint earthSize = 8;
GLint moonSize = 5;

//月球自轉、公轉方向
bool direction1 = false;//控制自轉
bool direction2 = false;//控制公轉

void init_observe()
{
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glMatrixMode(GL_MODELVIEW);
    gluLookAt(x, y, z, X, Y, Z, vx, vy, vz);
    glMatrixMode(GL_PROJECTION);
    glFrustum(-3.0, 3.0, -3.0, 3.0, 1.0, 30.0);
}

void drawPlanet(GLfloat x, GLfloat y, GLfloat z, GLfloat angle, GLint size)
{
    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();

    glTranslatef(x, y, z); //平移座標系
    glRotatef(angle, 0.0, 0.0, 1.0); //旋轉座標系
    glutWireSphere(size, 10, 10); //繪製線框球體，包括10條經線和10條緯線

    glPopMatrix();
}

void revolution()
{
    if (direction1)
    {
        moonAngle += 0.1;
        if (moonAngle >= 360)
            moonAngle -= 360;
    }
    else
    {
        moonAngle -= 0.1;
        if (moonAngle <= 0)
            moonAngle += 360;
    }
    if (direction2)
    {
        revoAngle += 0.01;
        if (revoAngle >= 360)
            revoAngle -= 360;
    }
    else
    {
        revoAngle -= 0.01;
        if (revoAngle <= 0)
            revoAngle += 360;
    }

    moonX = (GLdouble)distance*cos(revoAngle*pi/180);
    moonY = (GLdouble)distance*sin(revoAngle*pi/180); //計算月球座標
}

void keyboard(unsigned char k, int x, int y)
{
    if (k == 27)
        exit(0);

    int mod;
    if (k == 'd'||k == 'D')
    {
        mod = glutGetModifiers();
        if (mod == GLUT_ACTIVE_SHIFT) // shift 被按下
            direction1 = false;
        else
            direction1 = true;
    }
    else if (k == 'y'||k == 'Y')
    {
        mod = glutGetModifiers();
        if (mod == GLUT_ACTIVE_SHIFT)
            direction2 = false;
        else
            direction2 = true;
    }
}

void display()
{
    glClear(GL_COLOR_BUFFER_BIT);

    //draw earth
    glColor3f(0.0, 0.0, 1.0);
    drawPlanet(earthX, earthY, earthZ, 0, earthSize);
    //draw moon
    glColor3f(0.0, 1.0, 1.0);
    drawPlanet(moonX, moonY, moonZ, moonAngle, moonSize);

    glFlush();
    revolution();
    glutPostRedisplay();
}

void main(int argc, char**argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
    glutInitWindowPosition(10, 10);
    glutInitWindowSize(700, 700);
    glutCreateWindow("Planet");
    init_observe();

    glutDisplayFunc(display);
    glutKeyboardFunc(keyboard);
    glutMainLoop();
}