c++ - opengl画半圆

Question

我正在尝试画半个圆；当我运行代码时，我没有收到任何错误，但没有打印任何内容。有人可以让我知道我做错了什么吗？我尝试更改窗口位置，但没有成功。

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

void DrawHalfCircle()
 {
     glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
     glClear(GL_COLOR_BUFFER_BIT);
     glColor4f(1, 0, 0, 0);
     int number = 20; //number of vertices,
     float radius = 0.4f; // radius of the circle
     float twopi = 2.0f*3.14159f;
    glMatrixMode(GL_MODELVIEW); //operate in model view
    glLoadIdentity();//after every matrixmode, loadidentity is used.
    glTranslatef(0.5f, 0.0f, 0.0f); //to move the position of circle towards +ve x axis
glBegin(GL_TRIANGLE_FAN); //drawing circle using triangle fan
    glColor3f(0.0f, 0.0f, 1.0f); //blue in color
    glVertex2f(0.0f, 0.0f); //placing at the origin
    for (int i = 0; i <= 21; i++)
           glVertex2f(radius*cosf(i*twopi / number), radius*sinf(i*twopi / number));
     glEnd();
     glFlush();
}

主要内容

 int main()

{
       glutInit(&argc, argv);  //initialize glut
       glutInitWindowSize(640, 480); //width and height
       glutInitWindowPosition(0, 50); //bottom-left corner
       glutCreateWindow("drawing half a circle"); 
       glutDisplayFunc(DrawHalfCircle);
       glutMainLoop(); //loops itself again and again
      return 0;

}

Answer 1

这两个函数画了 2 个半圆，一个是实心的，另一个是空心的。(在 C++ 中)，我猜你的 main 是正确的。

void drawLeftCircle()   // the filled one
{
    float radius = 70;
    float twoPI = 2 * PI;

    glBegin(GL_TRIANGLE_FAN);

    for (float i = PI; i <= twoPI; i += 0.001)
        glVertex2f((sin(i)*radius), (cos(i)*radius));

    glEnd();
    glFlush();
}


void drawRightHalfCircle()  // the empty one
{
    float radius = 70;
    float twoPI = 2 * PI;

    glBegin(GL_POINTS);

    for (float i = 0.0; i <= twoPI / 2; i += 0.001)
        glVertex2f((sin(i)*radius), (cos(i)*radius));

    glEnd();
    glFlush();
}