用OpenGL绘制圆 [英] Drawing Circle with OpenGL

问题描述

我正在尝试使用C ++/OpenGl绘制简单的圆圈

I'm trying to draw simple circle with C++/OpenGl

我的代码是:

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

void Draw() {
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1.0, 1.0, 1.0);

    glBegin(GL_QUADS);
      glColor3f (0.0, 0.0, 0.0);

      glVertex3f (0.1, 0.1, 0.0);
      glVertex3f (0.9, 0.1, 0.0);
      glVertex3f (0.9, 0.9, 0.0);
      glVertex3f (0.1, 0.9, 0.0);

    glEnd();

    glFlush();
}

void DrawCircle(float cx, float cy, float r, int num_segments)
{
    glBegin(GL_LINE_LOOP);
    for(int ii = 0; ii < num_segments; ii++)
    {
        float theta = 2.0f * 3.1415926f * float(ii) / float(num_segments);//get the current angle

        float x = r * cosf(theta);//calculate the x component
        float y = r * sinf(theta);//calculate the y component

        glVertex2f(x + cx, y + cy);//output vertex

    }
    glEnd();
}


void Initialize() {
    glClearColor(1.0, 1.0, 1.0, 0.0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
}

int main(int iArgc, char** cppArgv) {
    glutInit(&iArgc, cppArgv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(950, 500);
    glutInitWindowPosition(200, 200);
    glutCreateWindow("Universum");
    Initialize();
    glutDisplayFunc(Draw);
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1.0, 1.0, 1.0);
    DrawCircle(0.5, 0.5, 0.2, 5);

    glutMainLoop();
    return 0;

}

我是OpenGL的初学者，现在我开始学习， 有人可以向我解释为什么我不认识这个圈子(我只看到黑框)， 谢谢！

I'm beginner with OpenGL and now i'm starting to learn, Can someone please explain me why i don't get the circle (i only see the black box), Thanks!

推荐答案

绘制圆后，您立即进入主glut循环，在其中设置了Draw()函数以每次绘制循环.因此，它可能是绘制圆，然后立即将其擦除并绘制正方形.您可能应该将DrawCircle()设置为glutDisplayFunc()，或者从Draw()调用DrawCircle().

It looks like immediately after you draw the circle, you go into the main glut loop, where you've set the Draw() function to draw every time through the loop. So it's probably drawing the circle, then erasing it immediately and drawing the square. You should probably either make DrawCircle() your glutDisplayFunc(), or call DrawCircle() from Draw().

这篇关于用OpenGL绘制圆的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！