c++ - OpenGL/Glut 无法在其上绘制 [

Question

我正在开发一个非常简单的 OpenGL 项目。我正在尝试模拟牛顿万有引力定律。这段代码还没有完成。我已经创建了粒子，并添加了绘图功能。我真的是 openGL 的新手，但我真的找不到为什么我只看到一个白色的窗口。我不能在上面画任何东西!不知道哪里错了。

#include <GLUT/GLUT.h>
#include <OpenGL/gl.h>
#include <stdlib.h>     /* srand, rand */
#include <time.h>       /* time */
#include <vector>
#include <stdio.h>
#include <iostream>
#include <math.h>
using namespace std;


GLfloat xRotated, yRotated, zRotated;
#define WIDTH 800
#define HEIGHT 1200
#define RAD 2000
// 6.67259(30)*10^-11 N(m/kg)^2

// mi escala sera la proporcion de 1 a 1 millón de toneladas.

#define GE 6.67259
void init(void)
{
    glClearColor(0,1,0,0);

}

typedef struct particulas{
    float x,y,z; // se va a comenza
    float factor;
    void Drawparticulas();
    particulas(float px,float py,float pz,float pfactor){
        x=px;
        y=py;
        z=pz;
        factor=pfactor;
    }
};

void particulas::Drawparticulas()
{
    // clear the drawing buffer.
    glPushMatrix();
    //glLoadIdentity();
    glTranslatef(x,y,z);
    //escala al tamaño pedido
    glScalef(factor,factor,factor);
    glBegin(GL_QUADS);        // Draw The Cube Using quads
    glColor3f(0.0f,1.0f,0.0f);    // Color Blue
    glVertex3f( 1.0f, 1.0f,-1.0f);    // Top Right Of The Quad (Top)
    glVertex3f(-1.0f, 1.0f,-1.0f);    // Top Left Of The Quad (Top)
    glVertex3f(-1.0f, 1.0f, 1.0f);    // Bottom Left Of The Quad (Top)
    glVertex3f( 1.0f, 1.0f, 1.0f);    // Bottom Right Of The Quad (Top)
    glColor3f(1.0f,0.5f,0.0f);    // Color Orange
    glVertex3f( 1.0f,-1.0f, 1.0f);    // Top Right Of The Quad (Bottom)
    glVertex3f(-1.0f,-1.0f, 1.0f);    // Top Left Of The Quad (Bottom)
    glVertex3f(-1.0f,-1.0f,-1.0f);    // Bottom Left Of The Quad (Bottom)
    glVertex3f( 1.0f,-1.0f,-1.0f);    // Bottom Right Of The Quad (Bottom)
    glColor3f(1.0f,0.0f,0.0f);    // Color Red
    glVertex3f( 1.0f, 1.0f, 1.0f);    // Top Right Of The Quad (Front)
    glVertex3f(-1.0f, 1.0f, 1.0f);    // Top Left Of The Quad (Front)
    glVertex3f(-1.0f,-1.0f, 1.0f);    // Bottom Left Of The Quad (Front)
    glVertex3f( 1.0f,-1.0f, 1.0f);    // Bottom Right Of The Quad (Front)
    glColor3f(1.0f,1.0f,0.0f);    // Color Yellow
    glVertex3f( 1.0f,-1.0f,-1.0f);    // Top Right Of The Quad (Back)
    glVertex3f(-1.0f,-1.0f,-1.0f);    // Top Left Of The Quad (Back)
    glVertex3f(-1.0f, 1.0f,-1.0f);    // Bottom Left Of The Quad (Back)
    glVertex3f( 1.0f, 1.0f,-1.0f);    // Bottom Right Of The Quad (Back)
    glColor3f(0.0f,0.0f,1.0f);    // Color Blue
    glVertex3f(-1.0f, 1.0f, 1.0f);    // Top Right Of The Quad (Left)
    glVertex3f(-1.0f, 1.0f,-1.0f);    // Top Left Of The Quad (Left)
    glVertex3f(-1.0f,-1.0f,-1.0f);    // Bottom Left Of The Quad (Left)
    glVertex3f(-1.0f,-1.0f, 1.0f);    // Bottom Right Of The Quad (Left)
    glColor3f(1.0f,0.0f,1.0f);    // Color Violet
    glVertex3f( 1.0f, 1.0f,-1.0f);    // Top Right Of The Quad (Right)
    glVertex3f( 1.0f, 1.0f, 1.0f);    // Top Left Of The Quad (Right)
    glVertex3f( 1.0f,-1.0f, 1.0f);    // Bottom Left Of The Quad (Right)
    glVertex3f( 1.0f,-1.0f,-1.0f);    // Bottom Right Of The Quad (Right)
    glEnd();            // End Drawing The Cube

    glPopMatrix();
}

vector<particulas*> mundo;


void Muevelos()
{

    //Dibujo las lineas del inicio

    glBegin(GL_LINES);
    glVertex3f(-RAD, -RAD, 0.0f);
    glVertex3f(RAD, -RAD, 0.0f);

    glVertex3f(RAD, -RAD, 0.0f);
    glVertex3f(RAD, RAD, 0.0f);

    glVertex3f(RAD, RAD, 0.0f);
    glVertex3f(-RAD, RAD, 0.0f);

    glVertex3f(-RAD, RAD, 0.0f);
    glVertex3f(-RAD, -RAD, 0.0f);

    glEnd();

    for(int i=0;i<mundo.size();i++){
        mundo[i]->Drawparticulas();
    }



}
// Not using this yet

void animation(void)
{
    for(int i=1;i<mundo.size();i++){

            float xd = mundo[0]->x-mundo[i]->x;
            float yd = mundo[0]->y-mundo[i]->y;
            float zd = mundo[0]->x-mundo[i]->x;
            float Distance = sqrt(xd*xd + yd*yd + zd*zd);

            // Ill apply the newtons law.

            //(mi*m2/D)g

            float F=(mundo[0]->factor*mundo[0]->factor/Distance)*GE;

            //Normalized Vector
            float nx,ny,nz;
            nx=mundo[i]->x/Distance;
            ny=mundo[i]->y/Distance;
            nz=mundo[i]->z/Distance;


            mundo[i]->x+=F*nx;
            mundo[i]->y+=F*ny;
            mundo[i]->z+=F*nz;
        }

}


void reshape(int x, int y)
{
    if (y == 0 || x == 0) return;  //Nothing is visible then, so return
    //Set a new projection matrix
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    //Angle of view:40 degrees
    //Near clipping plane distance: 0.5
    //Far clipping plane distance: 20.0
    gluPerspective(100.0,(GLdouble)x/(GLdouble)y,0,1000);
    glMatrixMode(GL_MODELVIEW);
    gluLookAt(-600,-600 , -600,
              0, 0, 0,
              0, 1, 0
              );
    glViewport(0,0,x,y);  //Use the whole window for rendering
}




int main(int argc, char** argv){

    mundo.resize(20);
    mundo[0]=new particulas(0,0,0,2); // centro

    for(int i=1;i<mundo.size();i++){
        float x=-RAD/2.0 + rand()%RAD;
        float y=-RAD/2.0 + rand()%RAD;
        float z=-RAD/2.0 + rand()%RAD;
        float r= 1+rand()%3;
       //  printf("%lf %lf %lf %lf\n",x,y,z,r);
        mundo[i]=new particulas(x,y,z,r);
    }

    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowPosition(1920/2-WIDTH/2,1080/2-HEIGHT/2);
    glutInitWindowSize(WIDTH,HEIGHT);
    glutCreateWindow("Giu");

    // glutInitWindowPosition(100, 100);


    glEnable(GL_DEPTH_TEST);
    //init();
    gluLookAt(-600,-600 , -600,
              0, 0, 0,
              0, 1, 0
              );

    glutDisplayFunc(Muevelos);
    glutReshapeFunc(reshape);
    //Set the function for the animation.
    //glutIdleFunc(animation);

    glutMainLoop();

    return 0;


}

Answer 1

1. gluPerspective() 的zNear 参数必须 大于零。
2. 在 gluLookAt() 之后您需要一个 glLoadIdentity() 否则您的模型 View 矩阵将在第二次调整窗口大小后变成乱码。
3. 您需要在显示回调的末尾使用 glutSwapBuffers()，以便您的后台缓冲区有朝一日可以真正进入前台缓冲区。
4. 您的对象/ View 缩放(可能)有很大偏差。

一个工作示例:

#include <GL/glut.h>

#include <vector>
using namespace std;

#include <glm/glm.hpp>
#include <glm/gtx/norm.hpp>
using namespace glm;


struct Particle
{
    dvec3 pos;
    dvec3 vel;
    double mass;
    dvec3 force;

    void Integrate( double dt )
    {
        const dvec3 accel = force / mass;

        // semi-implicit euler
        vel = vel + accel * dt;
        pos = pos + vel * dt;
    }
};

void Integrate( vector< Particle >& particles, double dt )
{
    // zero out force vectors for this tick
    for( size_t i = 0; i < particles.size(); ++i )
    {
        particles[i].force = dvec3( 0 );
    }

    // accumulate force vectors for each particle
    for( size_t i = 0; i < particles.size(); ++i )
    {
        for( size_t j = i+1; j < particles.size(); ++j )
        {
            Particle& p1 = particles[i];
            Particle& p2 = particles[j];

            // http://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation#Vector_form
            const double BigGee = 1.0;
            const dvec3 diff = ( p2.pos - p1.pos );
            const dvec3 rHat = glm::normalize( diff );
            const double r2 = glm::length2( diff );
            const dvec3 force = BigGee * ( ( p1.mass * p2.mass ) / r2 ) * rHat;

            p1.force += force;
            p2.force -= force;
        }
    }

    // update positions/velocities
    for( size_t i = 0; i < particles.size(); ++i )
    {
        particles[i].Integrate( dt );
    }
}

vector< Particle > particles;
void display()
{
    // use last frame time to calculate delta-t
    static int last = glutGet( GLUT_ELAPSED_TIME );
    int cur = glutGet( GLUT_ELAPSED_TIME );
    double dt = ( cur - last ) / 1000.0;
    last = cur;

    Integrate( particles, dt );


    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    double w = glutGet( GLUT_WINDOW_WIDTH );
    double h = glutGet( GLUT_WINDOW_HEIGHT );
    double ar = w / h;
    glOrtho( -100 * ar, 100 * ar, -100, 100, -1, 1 );

    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();

    // draw particles
    glPointSize( 5 );
    glEnableClientState( GL_VERTEX_ARRAY );
    glVertexPointer( 3, GL_DOUBLE, sizeof( Particle ), &particles[0].pos[0] );
    glDrawArrays( GL_POINTS, 0, particles.size() );
    glDisableClientState( GL_VERTEX_ARRAY );

    glutSwapBuffers();
}

void timer( int value )
{
    glutPostRedisplay();
    glutTimerFunc( 16, timer, 0 );
}

int main(int argc, char **argv)
{
    particles.resize( 2 );

    // "sun"
    particles[0].pos = dvec3( 0, 0, 0 );
    particles[0].vel = dvec3( 0, 0, 0 );
    particles[0].mass = 100000;

    // "planet"
    particles[1].pos = dvec3( 50, 0, 0 );
    particles[1].vel = dvec3( 0, -20, 0 );
    particles[1].mass = 1;

    glutInit( &argc, argv );
    glutInitDisplayMode( GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE );
    glutInitWindowSize( 600, 600 );
    glutCreateWindow( "GLUT" );

    glutDisplayFunc( display );
    glutTimerFunc( 0, timer, 0 );
    glutMainLoop();
    return 0;
}