openGL中的隨機點生成

Question

我想用openGL在屏幕上繪製100個點。這意味着每次運行程序時，屏幕上都會隨機顯示100個GL_POINTS。目前屏幕上只剩下一個點，並且它的位置是以前給出的。但是，我的隨機點只出現一段時間，然後消失。我不知道我錯過了什麼才能使它工作。以下是我的代碼

#include <stdlib.h> 
#include <GL/freeglut.h> 
#include <math.h> 

GLfloat cameraPosition[] = { 0.0, 0.2, 1.0 }; 

/* Random Star position */ 
GLfloat starX, starY, starZ; 
GLint starNum = 0; 

void myIdle(void){ 
    starNum += 1; 

    /* Generate random number between 1 and 4. */ 
    starX = 1.0 + static_cast <float> (rand())/(static_cast <float> (RAND_MAX/3.0)); 
    starY = 1.0 + static_cast <float> (rand())/(static_cast <float> (RAND_MAX/3.0)); 
    starZ = 1.0 + static_cast <float> (rand())/(static_cast <float> (RAND_MAX/3.0)); 

    /* Now force OpenGL to redraw the change */ 
    glutPostRedisplay(); 
} 

// Draw a single point 
void stars(GLfloat x, GLfloat y, GLfloat z){ 
    glBegin(GL_POINTS); 
    glColor3f(1.0, 0.0, 0.0); 
    glVertex3f(x, y, z); 
    glEnd(); 
} 

// Draw random points. 
void myDisplay(void){ 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
    glEnable(GL_LINE_SMOOTH); 
    glEnable(GL_BLEND); 
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); 
    glLoadIdentity(); 
    gluLookAt(cameraPosition[0], cameraPosition[1], cameraPosition[2], 0.0, 0.0, 0.0, 0.0, 1.0, 0.0); 

    /* They show up on the screen randomly but they disappear after starNum greater than 100 */ 
    if (starNum < 100){ 
     glPushMatrix(); 
     stars(starX, starY, starZ); 
     glPopMatrix(); 
    } 

    /* This point will remain on the screen. */ 
    glPushMatrix(); 
    stars(2.0, 2.0, 2.0); 
    glPopMatrix(); 

    /* swap the drawing buffers */ 
    glutSwapBuffers(); 
} 

void initializeGL(void){ 
    glEnable(GL_DEPTH_TEST); 
    glClearColor(0, 0, 0, 1.0); 
    glMatrixMode(GL_PROJECTION); 
    glLoadIdentity(); 
    glPointSize(2.0); 
    glOrtho(-4.0, 4.0, -4.0, 4.0, 0.1, 10.0); 
    glMatrixMode(GL_MODELVIEW); 
} 

void main(int argc, char** argv){ 
    glutInit(&argc, argv); 
    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH); 
    glutInitWindowSize(1800, 1000); 
    glutInitWindowPosition(100, 150); 
    glutCreateWindow("Random points"); 

    /* Register display function */ 
    glutDisplayFunc(myDisplay); 

    /* Register the animation function */ 
    glutIdleFunc(myIdle); 

    initializeGL(); 
    glutMainLoop(); 
} 

任何想法我錯過了什麼？

Answer 1

建立在@Reto_Koradi在他的評論中說過的話，每次你的顯示函數被調用時，你正在繪製2顆星。你正在畫一個隨機星（只要starnum小於100），然後你在位置（2,2,2）畫一顆星。你看到的恆星是（2,2,2）處的恆星。

什麼你可能想要做的是這樣的：

// Draw random points. 
void myDisplay(void){ 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
    glEnable(GL_LINE_SMOOTH); 
    glEnable(GL_BLEND); 
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); 
    glLoadIdentity(); 
    gluLookAt(cameraPosition[0], cameraPosition[1], cameraPosition[2], 0.0, 0.0, 0.0, 0.0, 1.0, 0.0); 

    /* They show up on the screen randomly but they disappear after starNum greater than 100 */ 
    for (starnum = 0; starnum < 100; starnum++) { 
     glPushMatrix(); 

     starX = 1.0 + static_cast <float> (rand())/(static_cast <float> (RAND_MAX/3.0)); 
     starY = 1.0 + static_cast <float> (rand())/(static_cast <float> (RAND_MAX/3.0)); 
     starZ = 1.0 + static_cast <float> (rand())/(static_cast <float> (RAND_MAX/3.0)); 

     stars(starX, starY, starZ); 
     glPopMatrix(); 
    } 

    /* This point will remain on the screen. */ 
    glPushMatrix(); 
    stars(2.0, 2.0, 2.0); 
    glPopMatrix(); 

    /* swap the drawing buffers */ 
    glutSwapBuffers(); 
} 

，然後刪除該改變的starnum和starX，starY和starZ從myIdle()函數值的代碼。

Answer 2

正如@Reet Koradi所說，我需要在每次調用顯示函數時畫出所有100顆星。爲此，我需要一個GLfloat數據結構，它在開始時存儲x，y，z隨機值，然後訪問數據數組以繪製星星，這將使它們全部保留在屏幕上。這裏是沒有'myIdle'功能的解決方案，一切都在'myDisplay'函數中完成。

/* Data structure for generating stars at random location */ 
typedef GLfloat star2[100]; 
star2 randomX = {}; 
star2 randomY = {}; 
star2 randomZ = {}; 

// Draw random points. 
void myDisplay(void){ 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
    glEnable(GL_LINE_SMOOTH); 
    glEnable(GL_BLEND); 
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); 
    glLoadIdentity(); 
    gluLookAt(cameraPosition[0], cameraPosition[1], cameraPosition[2], 0.0, 0.0, 0.0, 0.0, 1.0, 0.0); 

    /* Generate random number of stars */ 
    if (starNum < 100){ 
     /* This will store 100 stars' location to a data array. */ 
     for (starNum = 0; starNum < 100; starNum++) { 


     starX = -4.0 + static_cast <float> (rand())/(static_cast <float> (RAND_MAX/8.0)); 
     starY = -4.0 + static_cast <float> (rand())/(static_cast <float> (RAND_MAX/8.0)); 
     starZ = -4.0 + static_cast <float> (rand())/(static_cast <float> (RAND_MAX/8.0)); 

     randomX[starNum] = { starX }; 
     randomY[starNum] = { starY }; 
     randomZ[starNum] = { starZ }; 
     } 
    } 
    else{ 
     /* This will draw 100 stars on the screen */ 
     for (int i = 0; i < starNum; i++){ 
      glPushMatrix(); 
      stars(randomX[i],randomY[i], randomZ[i]); 
      glPopMatrix(); 
     } 
    } 

    /* swap the drawing buffers */ 
    glutSwapBuffers(); 
}