OpenGL的学习之路-3

zzz_zzzz_2023-11-14 19:20

前面1、2介绍的都是glut编程

下面就进行opengl正是部分啦。

1.绘制点

cpp 复制代码 
#include <iostream>
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>


void myMainWinDraw();

int main(int argc,char** argv) {
    glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
	glutInitWindowSize(400, 400);
	glutInitWindowPosition(0, 0);

	glutCreateWindow("Hello");

	glutDisplayFunc(myMainWinDraw);

	glutMainLoop();
	return 0;
}

void myMainWinDraw(){
    glClearColor(0.0,0.0,0.0,0.0);//设置清除色
    glClear(GL_COLOR_BUFFER_BIT); //清除颜色缓冲区

    float a[2];
    glGetFloatv(GL_POINT_SIZE_RANGE,a);
    std::cout<<a[0]<<"---"<<a[1]<<"\n";   //输出的是，点大小的范围（不过没有这么严格）

    glPointSize(10);   //设置点的大小

    glBegin(GL_POINTS);

    #if 0
    (0.5f,0.4f);
    (-0.5f,0.4f,0.0f);
    (0.0f,-0.4f,0.0f);
    #else
    glColor3f(1.0f,0.0f,0.0f);  //为点设置颜色
    glVertex3f(0.5f,0.4f,0.0f); //该语句可绘制

    glColor3f(0.0f,0.0f,1.0f);
    glVertex3f(-0.5f,0.4f,0.0f);

    glColor3f(0.0f,1.0f,0.0f);
    glVertex3f(0.0f,-0.4f,0.0f);
    #endif // 0
    
    glEnd();

    glFlush();
}

这里留下小思考题：

掷骰子是随机事件，现在平面上有三个点A、B、C，还有一个点P，位置可随机。令点A代表骰子的点数为1、4，点B代表骰子的点数为2、5，点C代表骰子的点数为3、6。现在开始扔，如果扔的点数为1或者4，那么取AP的中点作为新的P；如果扔到2或者5，则取BP的中点作为新的P；如果扔到的点数为3，6，则同理取CP的中点作为新的P。同时，要把每次取得的新的P绘制出来，并保持与相应的A或B或C同色。前面一定次数（如前20次），我们先不画点（还未进入稳态），后面再开始绘制。看看最终得到的图形是什么样子。

结果很奇妙！

明明是随机的，却呈现了规律性。赞叹数学、赞叹科学？是的，但我也想赞叹让我知道这个的我的老师。

2.绘制线

cpp 复制代码 
#include <iostream>
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>

void myMainWinDraw();

int main(int argc,char** argv) {
    glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
	glutInitWindowSize(400, 400);
	glutInitWindowPosition(0, 0);

	glutCreateWindow("Hello");

	glutDisplayFunc(myMainWinDraw);

	glutMainLoop();
	return 0;
}

void myMainWinDraw(){
    glClearColor(0.0,0.0,0.0,0.0);
    glClear(GL_COLOR_BUFFER_BIT);

    glLineWidth(2);

    glBegin(GL_LINES);

#if 0
    glVertex3f(0.5f,0.0f,0.0f);
    glVertex3f(0.5f,0.4f,0.0f);
    glVertex3f(0.0f,0.4f,0.0f);
    glVertex3f(0.0f,-0.4f,0.0f);
#else
    glColor3f(1.0f,0.0f,0.0f);
    glVertex3f(0.5f,0.0f,0.0f);

    glColor3f(0.0f,1.0f,0.0f);
    glVertex3f(0.5f,0.4f,0.0f);

    glColor3f(1.0f,0.0f,0.0f);
    glVertex3f(0.0f,0.4f,0.0f);

    glColor3f(0.0f,0.0f,1.0f);
    glVertex3f(0.0f,-0.4f,0.0f);

#endif

    glEnd();

    glFlush();

}

两点连成一条直线。点和点之间是配对的，如果给的点的个数是奇数，那么最后一个点没有找到和他配对的点，会不起作用。

关于颜色：

默认状态，是两边点颜色的线性插值，结果如下：

如果不想这样，就需要 glShadeModel(GL_FLAT) 变成：

glShadeModel(GL_SMOOTH) 和 glShadeModel(GL_FLAT) ！！

联系：绘制环

glBegin(GL_LINES_LOOP) :给出的两个相邻的点首尾相连，最后一个点和第一个点相连，构成环。两种颜色模式下：

3.绘制三角形

cpp 复制代码 
#include <iostream>
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>

void myMainWinDraw();

int main(int argc,char** argv) {
    glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
	glutInitWindowSize(400, 400);
	glutInitWindowPosition(0, 0);

	glutCreateWindow("Hello");

	glutDisplayFunc(myMainWinDraw);

	glutMainLoop();
	return 0;
}

void myMainWinDraw(){
    glClearColor(0.0,0.0,0.0,0.0);
    glClear(GL_COLOR_BUFFER_BIT);

    //glShadeModel(GL_FLAT); //GL_SMOOTH

    glBegin(GL_TRIANGLES);

#if 0
    glVertex3f(0.5f,0.0f,0.0f);
    glVertex3f(0.5f,0.4f,0.0f);
    glVertex3f(0.0f,0.4f,0.0f);

    glVertex3f(0.0f,-0.4f,0.0f);
    glVertex3f(0.3f,-0.4f,0.0f);
    glVertex3f(0.0f,-0.2f,0.0f);
#else
    glColor3f(1.0f,0.0f,0.0f);
    glVertex3f(0.5f,0.0f,0.0f);

    glColor3f(0.0f,1.0f,0.0f);
    glVertex3f(0.5f,0.4f,0.0f);

    glColor3f(1.0f,0.0f,0.0f);
    glVertex3f(0.0f,0.4f,0.0f);

    glColor3f(0.0f,0.0f,1.0f);
    glVertex3f(0.0f,-0.4f,0.0f);

    glColor3f(1.0f,0.0f,1.0f);
    glVertex3f(0.3f,-0.4f,0.0f);

    glColor3f(0.0f,1.0f,1.0f);
    glVertex3f(0.0f,-0.2f,0.0f);

#endif

    glEnd();

    glFlush();

}

三个点一组，绘制一个三角形。

推广：

（后面几个平时用不太到）

4.绘制的线型

cpp 复制代码 
#include <iostream>
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>

void myMainWinDraw();

int main(int argc,char** argv)
{
    glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
	glutInitWindowSize(400, 400);
	glutInitWindowPosition(0, 0);

	glutCreateWindow("Hello");

	glutDisplayFunc(myMainWinDraw);

	glutMainLoop();
	return 0;
}

void myMainWinDraw(){
    glClearColor(0.0,0.0,0.0,0.0);
    glClear(GL_COLOR_BUFFER_BIT);

    glLineWidth(2);
    glEnable(GL_LINE_STIPPLE);

    glLineStipple(1,0xF0F0);  //第一个参数是重复度、第二个参数代表线型
    glBegin(GL_LINES);
    glVertex3f(0.5f, 0.4f ,0.0f);
    glVertex3f(-0.5f, 0.4f ,0.0f);
    glEnd();

    glLineWidth(10);
    glLineStipple(5,0xF0F0);
    glColor3f(1.0f,0.0f,0.0f);
    glBegin(GL_LINES);
    glVertex3f(0.5f, 0.0f, 0.0f);
    glVertex3f(-0.5f, 0.0f,0.0f);
    glEnd();

    glLineWidth(20);
    glLineStipple(3,0x7555);
    glColor3f(1.0f,1.0f,0.0f);
    glBegin(GL_LINES);
    glVertex3f(0.5f, -0.4f, 0.0f);
    glVertex3f(-0.5f, -0.8f,0.0f);
    glEnd();

    glLineWidth(5);
    glBegin(GL_LINE_LOOP);
    glVertex3f(-0.8f,  0.8f, 0.0f);
    glVertex3f(-0.8f, -0.8f, 0.0f);
    glVertex3f( 0.8f, -0.8f, 0.0f);
    glVertex3f( 0.8f,  0.8f, 0.0f);
    glEnd();

    glFlush();

}

新的知识点：

  1. glEnable(GL_LINE_STIPPLE) ：将开关打开

  2. glLineStipple(1,0xF0F0）：第一个参数是重复度，第二个参数是线型。这里是，1111000011110000。如果将第一个参数改为2，那么将变成1111111100000000...这个样子。

绘制结果：

5.多边形绘制的模式（填充/线框）

cpp 复制代码 
#include <iostream>
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>

void myMainWinDraw();

int main(int argc,char** argv)
{
    glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
	glutInitWindowSize(400, 400);
	glutInitWindowPosition(0, 0);

	glutCreateWindow("Hello");

	glutDisplayFunc(myMainWinDraw);

	glutMainLoop();
	return 0;
}

void myMainWinDraw(){
    glClearColor(0.0,0.0,0.0,0.0);
    glClear(GL_COLOR_BUFFER_BIT);

    glDisable(GL_LIGHTING);

    glPolygonMode(GL_FRONT,GL_FILL);
    glPolygonMode(GL_BACK,GL_LINE);
    glBegin(GL_TRIANGLES);
    glVertex2f(-1.0f, 0.0f);
    glVertex2f( 0.0f, 0.0f);
    glVertex2f( 0.0f, 1.0f);
    glEnd();

    glPolygonMode(GL_FRONT,GL_LINE);
    glBegin(GL_TRIANGLES);
    glVertex2f( 1.0f, 0.0f);
    glVertex2f( 0.0f, 1.0f);
    glVertex2f( 0.0f, 1.0f);
    glEnd();


    glPolygonMode(GL_FRONT_AND_BACK,GL_FILL);
    glBegin(GL_TRIANGLES);
    glVertex2f(  0.0f, 0.0f);
    glVertex2f( -1.0f, 0.0f);
    glVertex2f(  0.0f,-1.0f);
    glEnd();

    glFrontFace(GL_CW);
    glPolygonMode(GL_BACK,GL_FILL);
    glPolygonMode(GL_FRONT,GL_LINE);
    glBegin(GL_TRIANGLES);
    glVertex2f(  0.0f, 0.0f);
    glVertex2f(  0.0f,-1.0f);
    glVertex2f(  1.0f, 0.0f);
    glEnd();

    glFlush();
}

新的知识点：

  1. glPolygonMode(GL_FRONT,GL_FILL)：设置正面或者背面的填充方式为GL_FILL或者GL＿LINE模式。

  2. glFrontFace(GL_CW)：初始状态将CCW方向（点的顺序）视为正面，该语句将CW方向转为正面。

6.多边形填充的效果

填充图形的定义：

下面就是glBegin()和glEnd() 了

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