c++ - 具有两个循环的OpenGL，一个循环不起作用

Question

我的 OpenGL 程序运行不正常。在 drawScene() 函数中，我创建了两个循环。一个循环用于 GL_LINES 另一个循环用于 GL_POINTS。 GL_LINES 循环工作正常，但 GL_POINTS 循环不起作用。任何帮助表示赞赏。

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

#define PI 3.14159265

using namespace std;

//Called when a key is pressed
void handleKeypress(unsigned char key, int x, int y) {
    switch (key) {
        case 27: //Escape key
            exit(0);
    }
}

//Initializes 3D rendering
void initRendering() {
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_COLOR_MATERIAL); //Enable color
    glClearColor(0.7f, 0.9f, 1.0f, 1.0f); //Change the background to sky blue
}

//Called when the window is resized
void handleResize(int w, int h) {
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45.0, (double)w / (double)h, 1.0, 200.0);
}

float _angle = 0.0f;
float _cameraAngle = 0.0f;
float x = -1.5;
float y = -0.5;

//Draws the 3D scene
void drawScene() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();


    glLineWidth (9.0f);
    glBegin(GL_LINES);

    glColor3f(1.0f, 0.0f, 0.0f);
    double r = 0.5;

    for(int c = 0;c<=360;c++){
        double y = r*cos (c*PI/180);
        double x = r*sin (c*PI/180);
        glVertex3d(x,y,-5.0);
        glVertex3d(0.0,0.0,-5.0);
    }
    glEnd();


    glPointSize (7.0f);
    glBegin(GL_POINTS);

    glColor3f(0.0f, 1.0f, 0.0f);
    double r = 1.0;

    for(int c = 0;c<=360;c++){
        double y = r*cos (c*PI/180);
        double x = r*sin (c*PI/180);
        glVertex3d(x,y,-5.0);
        //glVertex3d(0.0,0.0,-5.0);
    }
    glEnd();

    glutSwapBuffers();
    //glutPostRedisplay();
}

void update(int value) {
    _angle += 2.0f;
    if (_angle > 360) {
        _angle -= 360;
    }

    glutPostRedisplay();
    glutTimerFunc(60, update, 0);
}

int main(int argc, char** argv) {
    //Initialize GLUT
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(400, 400);

    //Create the window
    glutCreateWindow("two circle");
    initRendering();

    //Set handler functions
    glutDisplayFunc(drawScene);
    glutKeyboardFunc(handleKeypress);
    glutReshapeFunc(handleResize);

    glutTimerFunc(25, update, 0); //Add a timer

    glutMainLoop();
    return 0;
}

Answer 1

现在，您在两个地方声明变量 r:设置 double r = 0.5; 的地方和 double r = 1.0;

尝试将其更改为:

double r = 0.5;
//First loop

r = 1.0;
//Second loop