Assignment 2 使用OpenGL画安卓机器人

一. 实现简述

Assignment 2 Report

目标:画一个安卓机器人。

代码结构:在 glutDisplayFunc(drawRobot)中的参数 drawRobot 函数是实 现画机器人的最外层函数,其中包括画脸、画身体、画手和画脚。每个函数又继 续细分画的步骤和方法。如下图所示:

二. 心得体会
这次任务让我对 OpenGl 有了初步认识。通过阅读课本和网上的资料,掌握

使用 OpenGl 的基本功能,比如如何画基本的点、线和多边形。并理解了一些之
前没明白的重要概念,比如 glLoadIdentity 和 glPushMatrix、glPopMatrix 的区
别。根据我现在的理解,glLoadIdentity 是将矩阵堆栈中栈顶的矩阵置为单位矩
阵,相当于坐标原点回到一开始的设置,也就忽略了之前平移、旋转等导致坐标
原点位置的改变。而 glPushMaxtrix 和 glPopMatrix 则是用于将当前矩阵压入栈
中,然后执行一些变换,这些变换是基于之前已经变换过的坐标,最后再出栈,
回到入栈前的坐标。

接下来我将继续学习 OpenGL 更多强大的功能。

代码如下：

#include <gl/glut.h>
#include <math.h>

int i;
const GLfloat PI = 3.1415926536f;
const int n = 1000;
const GLfloat eyeR = 0.025f; //radius of eye
const GLfloat faceR = 0.3f; //radius of face
const GLfloat bodyR = 0.05f; //radius of the corner of body
const GLfloat limbR = 0.06f; //radius of limb in both ends

void drawLimb(void) {
    //draw a half circle at one end
    glBegin(GL_POLYGON);
    for (i = 0; i < n; i++) {
        glVertex2f(limbR * cos(2 * PI / n * i), limbR * sin(2 * PI / n * i));
    }
    glEnd();

    //draw a rectangle
    glTranslatef(-0.06f, 0.0f, 0.0f);
    glRectf(0.0f, 0.0f, 0.12f, -0.3f);
    glEnd();

    //draw a half circle at the other end
    glTranslatef(0.06f, -0.3f, 0.0f);
    glBegin(GL_POLYGON);
    for (i = 0; i < n; i++) {
        glVertex2f(limbR * cos(2 * PI / n * i), limbR * sin(2 * PI / n * i));
    }
    glEnd();
    glFlush();
}

void drawHands(void)
{
    glLoadIdentity();
    glTranslatef(-0.38f, 0.2f, 0.0f);
    drawLimb();

    glLoadIdentity();
    glTranslatef(0.38f, 0.2f, 0.0f);
    drawLimb();
}

void drawBody(void)
{
    glLoadIdentity();

    //draw a rectangle first
    glTranslatef(-0.3f, 0.25f, 0.0f);
    glRectf(0.0f, 0.0f, 0.6f, -0.45f);
    glEnd();

    //draw a half circle at the left bottom
    glTranslatef(0.05f, -0.45f, 0.0f);
    glBegin(GL_POLYGON);
    for (i = 0; i < n; i++) {
        if (sin(2 * PI / n * i) < 0) {
            glVertex2f(bodyR * cos(2 * PI / n * i), bodyR * sin(2 * PI / n * i));
        }
    }
    glEnd();

    //draw a half circle at the right bottom
    glTranslatef(0.5f, 0.0f, 0.0f);
    glBegin(GL_POLYGON);
    for (i = 0; i < n; i++) {
        if (sin(2 * PI / n * i) < 0) {
            glVertex2f(bodyR * cos(2 * PI / n * i), bodyR * sin(2 * PI / n * i));
        }
    }
    glEnd();

    //draw the bottom rectangle
    glRectf(0.0f, 0.0f, -0.5f, -0.05f);
    glEnd();

    glFlush();
}

void drawLegs(void)
{
    glLoadIdentity();
    glTranslatef(-0.11f, -0.08f, 0.0f);
    drawLimb();

    glLoadIdentity();
    glTranslatef(0.11f, -0.08f, 0.0f);
    drawLimb();

}

void drawLine(void) {
    glLineWidth(5.0f);

    glBegin(GL_LINES);
    glVertex2f(0.0f, 0.0f);
    glVertex2f(0.0f, 0.15f);
    glEnd();

    glFlush();
}

void drawEye(void) {
    glColor3f(1.0f, 1.0f, 1.0f);
    glBegin(GL_POLYGON);
    for (i = 0; i < n; i++) {
        glVertex2f(eyeR * cos(2 * PI / n * i), eyeR * sin(2 * PI / n * i));
    }
    glEnd();
    glColor3ub(164, 202, 57);

    glFlush();
}

void drawFaceShape(void) {
    glBegin(GL_POLYGON);

    for (i = 0; i < n; i++) {
        if (sin(2 * PI / n * i) >= 0) {
            glVertex2f(faceR * cos(2 * PI / n * i), faceR * sin(2 * PI / n * i));
        }
    }
    glEnd();
    glFlush();
}

void drawFace(void)
{
    glLoadIdentity();
    glTranslatef(0.0f, 0.27f, 0.0f);
    drawFaceShape();//draw the overall shape of face

    //draw left eye
    glLoadIdentity();
    glTranslatef(-0.13f, 0.42f, 0.0f);
    drawEye();

    //draw right eye
    glLoadIdentity();
    glTranslatef(0.13f, 0.42f, 0.0f);
    drawEye();

    //draw left line
    glLoadIdentity();
    glTranslatef(-0.13f, 0.5f, 0.0f);
    glRotated(30.0f, 0.0f, 0.0f, 1.0f);
    drawLine();

    //draw right line
    glLoadIdentity();
    glTranslatef(0.13f, 0.5f, 0.0f);
    glRotated(-30.0f, 0.0f, 0.0f, 1.0f);
    drawLine();

}

void drawRobot(void)
{
    glClearColor(1.0f, 1.0f, 1.0f, 0.0f);//set background color to white
    glClear(GL_COLOR_BUFFER_BIT);

    glLoadIdentity();
    glColor3ub(164, 202, 57);//color of robot

    drawFace();
    drawBody();
    drawHands();
    drawLegs();
}

int main(int argc, char *argv[])
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
    glutInitWindowPosition(100, 100);
    glutInitWindowSize(400, 400);
    glutCreateWindow("Android Robot");
    glutDisplayFunc(drawRobot);
    glutMainLoop();

    return 0;
}