openGL实现二维图形和三维图形

  openGL是一个强大的底层图形库,其命令最初的时候使用C语言实现的。openGL定义了一个图形程序接口,常用于制作处理三维图像,功能强大,调用方便,在图像处理十分受欢迎。

  实现图形主要使用的是openGL的一个工具包:GLUT。

  GLUT (pronounced like the glut in gluttony) is the OpenGL Utility Toolkit, a window system independent toolkit for writing OpenGL programs. It implements a simple windowing application programming interface (API) for OpenGL.

  GLUT is designed for constructing small to medium sized OpenGL programs. While GLUT is well-suited to learning OpenGL and developing simple OpenGL applications, GLUT is not a full-featured toolkit so large applications requiring sophisticated user interfaces are better off using native window system toolkits like Motif. GLUT is simple, easy, and small.

  GLUT对于大型的项目来说可能功能不全,它主要针对一些中小型的openGL项目而设计。

  1.实现二维图像相对简单些,直接下代码:

#include <GL/glut.h>

void Rectangle(void) {
//gl开头的函数为openGL的标准函数 //(使用当前缓冲区的值来)清除指定的缓冲区
glClear(GL_COLOR_BUFFER_BIT);

     //画矩形
//glRectf(-0.5f, -0.5f, 0.5f, 0.5f); //画直线
glBegin(GL_LINES);
glVertex2f(0.5f, 0.5f);
glVertex2f(-0.5f, -0.5f);
glEnd(); //刷新缓冲,保证绘图命令能被执行
glFlush();
} int main(int argc, char *argv[]) { //初始化GLUT library
glutInit(&argc, argv);
//对窗口的大小进行初始化
glutInitWindowSize(300, 300);
// 设置窗口出现的位置
//glutInitWindowPosition(int x, int y);
//初始化程序展示模式
glutInitDisplayMode(GLUT_RGBA);
glutCreateWindow("project of openGL");
//win: 指定子窗口的父窗口
//glutCreateSubWindow(int win, int x, int y, int width, int height);
//为当前窗口设置函数回调,用于画图
glutDisplayFunc(&Rectangle);
//进行glut事件循环,否则看不到图形效果(一闪而过)
glutMainLoop(); return 0;
}

  实现效果:

  openGL实现二维图形和三维图形      openGL实现二维图形和三维图形

  也可以在窗口中画一个圆:

#include <math.h>
GLfloat r = 0.5f;
GLfloat PI = 3.141592653f;
int pre = 30;
glBegin(GL_POLYGON);//画多边形
for (int i = 0; i < pre; i++) {
glVertex2f(r * cos(2 * PI*i / pre), r * sin(2 * PI*i / pre));
}
glEnd();

  实际上这个圆并不是圆,而是多边形的近似。GL_POLYGON用于绘制多边形,边数达到一定程度,显示出来的形状近似于圆。

  openGL实现二维图形和三维图形

  2.接下来来实现三维图像Cube。

  三维变换:  

  模型视图变换(GL_MODELVIEW):从“相对移动”的观点来看,改变观察点的位置与方向和改变物体本身的位置与方向具有等效性。

  透视投影变换(GL_PROJECTION):定义一个可视空间,可视空间以外的物体不会被绘制到屏幕上。

  视口变换(glViewPort):通常情况下,程序默认像素填充整个窗口,通过视口变换设置像素在窗口上的填充情况。

  每次对物体进行变换的时候,都需要先设置当前操作的矩阵为某种变换的矩阵,在进行变换之前还需要将矩阵转换为单位矩阵才能进行操作。

glMatrixMode(GL_PROJECTION);
glLoadIdentity();

  完整代码:

#include <GL/glut.h>
#include <math.h> void setCube(void) {
glClearColor(1.0, 1.0, 1.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(0, 0, 0);//设置黑色
glLoadIdentity();//加载单位矩阵
gluLookAt(6, 0, 2.5, 0, 0, 0, 1, 1, 0);
//前三个参数设置观察者的观察位置,中三个参数设置观察点的位置,后三个参数设置观察者的观察方向
glLineWidth(2.0f);//设置边的像素宽,默认为1.0f
glutWireCube(2.0);
glFlush();
} void drawCube(void) {
glClearColor(1.0, 1.0, 1.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity();
gluLookAt(4, 0, 1.5, 0, 0, 0, 1, 1, 0); //绘制正方体的面
glColor3f(0, 1, 0);
glBegin(GL_QUADS);
//---1---
glNormal3f(-1, 0, 0);//设置点的法向量
glVertex3f(0.5, 0.5, 0.5);
glVertex3f(0.5, -0.5, 0.5);
glVertex3f(0.5, -0.5, -0.5);
glVertex3f(0.5, 0.5, -0.5);
//---2---
glNormal3f(-1, 0, 0);
glVertex3f(-0.5, 0.5, 0.5);
glVertex3f(-0.5, -0.5, 0.5);
glVertex3f(-0.5, -0.5, -0.5);
glVertex3f(-0.5, 0.5, -0.5);
//---3---
glNormal3f(0, 1, 0);
glVertex3f(0.5, 0.5, 0.5);
glVertex3f(-0.5, 0.5, 0.5);
glVertex3f(-0.5, 0.5, -0.5);
glVertex3f(0.5, 0.5, -0.5);
//---4---
glNormal3f(0, -1, 0);
glVertex3f(0.5, -0.5, 0.5);
glVertex3f(-0.5, -0.5, 0.5);
glVertex3f(-0.5, -0.5, -0.5);
glVertex3f(0.5, -0.5, -0.5);
//---5---
glNormal3f(0, 0, 1);
glVertex3f(0.5, 0.5, 0.5);
glVertex3f(-0.5, 0.5, 0.5);
glVertex3f(-0.5, -0.5, 0.5);
glVertex3f(0.5, -0.5, 0.5);
//---6---
glNormal3f(0, 0, -1);
glVertex3f(0.5, 0.5, 0.5);
glVertex3f(-0.5, 0.5, 0.5);
glVertex3f(-0.5, -0.5, 0.5);
glVertex3f(0.5, -0.5, 0.5);
glEnd(); //draw
glColor3f(0, 0, 0);
glLineWidth(2.0f);
//绘制正方体的边
glBegin(GL_LINES);
//---1---
glVertex3f(0.5, 0.5, 0.5);
glVertex3f(-0.5, 0.5, 0.5);
glVertex3f(-0.5, 0.5, 0.5);
glVertex3f(-0.5, -0.5, 0.5);
glVertex3f(-0.5, -0.5, 0.5);
glVertex3f(0.5, -0.5, 0.5);
glVertex3f(0.5, -0.5, 0.5);
glVertex3f(0.5, 0.5, 0.5);
//---2---
glVertex3f(0.5, 0.5, -0.5);
glVertex3f(-0.5, 0.5, -0.5);
glVertex3f(-0.5, 0.5, -0.5);
glVertex3f(-0.5, -0.5, -0.5);
glVertex3f(-0.5, -0.5, -0.5);
glVertex3f(0.5, -0.5, -0.5);
glVertex3f(0.5, -0.5, -0.5);
glVertex3f(0.5, 0.5, -0.5);
//---3---
glVertex3f(0.5, 0.5, 0.5);
glVertex3f(0.5, -0.5, 0.5);
glVertex3f(0.5, -0.5, 0.5);
glVertex3f(0.5, -0.5, -0.5);
glVertex3f(0.5, -0.5, -0.5);
glVertex3f(0.5, 0.5, -0.5);
glVertex3f(0.5, 0.5, -0.5);
glVertex3f(0.5, 0.5, 0.5);
//---4---
glVertex3f(-0.5, 0.5, 0.5);
glVertex3f(-0.5, -0.5, 0.5);
glVertex3f(-0.5, -0.5, 0.5);
glVertex3f(-0.5, -0.5, -0.5);
glVertex3f(-0.5, -0.5, -0.5);
glVertex3f(-0.5, 0.5, -0.5);
glVertex3f(-0.5, 0.5, -0.5);
glVertex3f(-0.5, 0.5, 0.5);
glEnd();
glFlush();
} void threeD(int w, int h) {
glViewport(0, 0, (GLsizei)w, (GLsizei)h);//调整视图窗口大小
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glFrustum(-1.0, 1.0, -1.0, 1.0, 2.0, 10.0);
glMatrixMode(GL_MODELVIEW); } int main(int argc, char *argv[]) { //初始化GLUT library
glutInit(&argc, argv);
//对窗口的大小进行初始化
glutInitWindowSize(500, 500);
// 设置窗口出现的位置
//glutInitWindowPosition(int x, int y);
//初始化程序展示模式
glutInitDisplayMode(GLUT_RGBA);
glutCreateWindow("project of openGL");
//为当前窗口设置函数回调,用于画图
glutDisplayFunc(drawCube);
//窗口改变时的函数
glutReshapeFunc(threeD);
glutMainLoop(); return 0;
}

  可以调用openGL的glutWireCube(GLFloat size)来绘制立体正方形,如setCube函数。

  我想要实现带有黑色边缘的绿色正方体,必须对正方体进行绘制,如drawCube函数。

  实现效果:

  openGL实现二维图形和三维图形

  openGL实现二维图形和三维图形

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