用OpenGL繪製一個帶有四個三角形的四面體

Question

我決定手動創建一個四面體（4個三角形）並旋轉它。它有點工作，唯一的問題是其中一個三角形從未畫出。在我的示例代碼中，前三角形（紅色）首先繪製，但是當我渲染它時，它從不出現。出現左半邊三角形（白色）和直角三角形（藍色）的一半。但是，當我更改代碼並將前三角形的三個頂點放在其他三角形的頂點之後時，我確實得到了前三角形。儘管如此，另外兩個三角形中的一個消失了。我究竟做錯了什麼？

#include <stdio.h> 
#include <stdlib.h> 
#include <GLUT/glut.h> 
#include <OpenGL/glu.h> 
#include <OpenGL/gl.h> 

float posx = 0; 
float posy = 0; 

void drawLines(void) 
{ 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
    //THIS ROTATES THE WHOLE SCENCE 
    /*glMatrixMode(GL_MODELVIEW); 
    glLoadIdentity(); 
    glRotatef(posx, 0.0f, 1.0f, 0.0f);*/ 

    //THIS ROTATES ONLY THE OBJECTS INSIDE THE GLPUSHMATRIX AND GLPOPMATRIX FUNCTIONS 
    glPushMatrix(); 
    glRotatef(posx, 0.0f, 1.0f, 0.0f); 

    //TETAEDRON BY HAND 
    glBegin(GL_TRIANGLES); 

    //front triangle 
    glColor4f(1.0f, 0.0f, 0.0f, 1.0f); 
    glVertex3f(0.0f, 5.0f, 0.0f); 
    glVertex3f(-5.0f, -5.0f, 0.0f); 
    glVertex3f(5.0f, -5.0f, 0.0f); 

    //right side triangle 
    glColor4f(0.0f, 0.0f, 1.0f, 1.0f); 
    glVertex3f(5.0f, -5.0f, 0.0f); 
    glVertex3f(0.0f, 5.0f, 0.0f); 
    glVertex3f(0.0f, -5.0f, -5.0f); 

    //left side triangle 
    glColor4f(1.0f, 1.0f, 1.0f, 1.0f); 
    glVertex3f(-5.0f, -5.0f, 0.0f); 
    glVertex3f(0.0f, 5.0f, 0.0f); 
    glVertex3f(0.0f, -5.0f, -5.0f); 

    //bottom triangle 
    glColor4f(0.0f, 1.0f, 0.0f, 1.0f); 
    glVertex3f(-5.0f, -5.0f, 0.0f); 
    glVertex3f(5.0f, -5.0f, 0.0f); 
    glVertex3f(0.0f, -5.0f, -5.0f); 

    glEnd(); 

    //glutSolidTeapot(5.0); 
    glPopMatrix(); 
    glutWireTeapot(5.0); 
    glFlush(); 
} 

void init() 
{ 
    /*glClearDepth(1.0f); 
    glEnable(GL_DEPTH_TEST); 
    glDepthFunc(GL_LEQUAL);*/ 
    glClearColor(0, 0, 0, 0); 
    glMatrixMode(GL_PROJECTION); 
    glLoadIdentity(); 
    glOrtho(-10.0f, 10.0f, -10.0f, 10.0f, -10.0f, 10.0f);//range of x,y,z axis 
    //gluOrtho2D(0.0f, 500.0f, 500.0f, 0.0f);//setup the camera in 2d mode 

    glMatrixMode(GL_MODELVIEW); 
    glLoadIdentity(); 
} 

void keyboard(unsigned char key, int x, int y) 
{ 
    switch (key) 
    { 
     case 'd':posx+=10; 
      printf("derecha %f\n",posx); 
      break; 
     case 'a':posx-=10; 
      printf("izquierda\n"); 
      break; 
     case 'w':posy-=10; 
      printf("arriba\n"); 
      break; 
     case 's':posy+=10; 
      printf("abajo\n"); 
      break; 
    } 

//glMatrixMode(GL_MODELVIEW); 
//glLoadIdentity(); 
//glViewport(100.0f, 100.0f, 500.0f, 500.0f); 
//glTranslatef(posx, posy, 0.0); 
if(posx>=360) 
    posx = 0; 
//glRotatef(posx, 0.0f, 1.0f, 0.0f); 
} 

int main(int argc, const char * argv[]) 
{ 

    // insert code here... 

    glutInit(&argc, argv); 
    glutInitDisplayMode(GLUT_RGBA | GLUT_SINGLE); 
    glutInitWindowPosition(400, 200); 
    glutInitWindowSize(500, 500); 
    glutCreateWindow("OpenGLTest"); 

    init(); 

    glutDisplayFunc(drawLines); 
    glutIdleFunc(drawLines); 
    glutKeyboardFunc(keyboard); 
    glutMainLoop(); 
    return 1; 
} 

Answer 1

您需要啓用深度測試。目前它已在您的init()函數中註釋掉。