OpenGL glDrawElements只有黑屏 [英] OpenGL glDrawElements only Black Screen

问题描述

我试图绘制一个立方体，使用glDrawElements函数，但即使下面的简单代码只给了我一个黑色的屏幕。如果有帮助，我在XCode 6上编程。

  // 
 // main.cpp 
 //版权所有（c）2014 Guilherme Cardoso。版权所有。 
 // 
 
 #include< iostream> 
 #include< OpenGL / OpenGL.h> 
 #include< GLUT / GLUT.h> 
 #include< vector> 
 #include< math.h> 
 
 const GLfloat width = 500; 
 const GLfloat height = 500; 
 
 GLubyte cubeIndices [24] = {0,3,2,1,2,3,7,6 
，0,4,7,3,1,2,6,5 ，4,5,6,7,0,1,5,4}; 
 
 GLfloat vertices [] [3] = 
 {{-1.0，-1.0，-1.0}，{1.0，-1.0，-1.0}，
 {1.0,1.0 ，-1.0}，{-1.0,1.0，-1.0}，{-1.0，-1.0,1.0}，
 {1.0，-1.0,1.0}，{1.0,1.0,1.0}，{-1.0， 1.0,1.0}}; 
 
 GLfloat colors [] [3] = 
 {{0.0,0.0,0.0}，{1.0,0.0,0.0}，
 {1.0,1.0,0.0}，{ 0.0,1.0,0.0}，{0.0,0.0,1.0}，
 {1.0,0.0,1.0}，{1.0,1.0,1.0}，{0.0,1.0,1.0}}; 
 
 void display（）{
 glEnableClientState（GL_COLOR_ARRAY）; 
 glEnableClientState（GL_VERTEX_ARRAY）; 
 glColorPointer（3，GL_FLOAT，0，colors）; 
 glVertexPointer（3，GL_FLOAT，0，vertices）; 
 
 // glDrawArrays（GL_QUADS，0，24）; 
 glDrawElements（GL_QUADS，24，GL_UNSIGNED_BYTE，cubeIndices）; 
 glDisableClientState（GL_VERTEX_ARRAY）; 
 glutSwapBuffers（）; 
} 
 
 void mouse（int button，int state，int x，int y）{
 
} 
 
 void keyboard char（）{
 if（key =='q'|| key =='Q'）exit（0）; 
} 
 
 void init（）{
 glEnable（GL_DEPTH_TEST）; 
 glMatrixMode（GL_PROJECTION）; 
 glLoadIdentity（）; 
 gluOrtho2D（0，width，height，0）; 
 glMatrixMode（GL_MODELVIEW）; 
 
 glClearColor（1.0，1.0，1.0,1.0）; 
 //glColor3f(0.0,0.0,0.0）; 
} 
 
 void void（）{
 
} 
 
 int main（int argc，char ** argv）{
 glutInit（& argc，argv）; 
 glutInitDisplayMode（GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH）; 
 glutInitWindowSize（width，height）; 
 glutCreateWindow（Assignment 3）; 
 glutPositionWindow（0，0）; 
 
 
 glutDisplayFunc（display）; 
 glutMouseFunc（mouse）; 
 glutKeyboardFunc（keyboard）; 
 glutIdleFunc（idle）; 
 
 init（）; 
 glutMainLoop（）; 
} 
  

我已经检查过一些教程， 。

解决方案

实际上，你的代码正在绘制多维数据集。仔细观察：P

/ p>

主要的问题是你的投影。初始GL查看量是一个-1到1的立方体，但是你正在绘制的立方体是 -1到1.调用 gluOrtho2D 在OpenGL坐标中定义投影，它与像素相同，但是因为您的立方体是-1到1，它只有两个像素，其余的是在屏幕外。

而是将 c> gluOrtho2D ，将 Z 维度-1设为1，只允许您设定 / ，并创建一个略大的投影...

  glOrtho（-2， -2，2，-2,2）; 
  

---

注意：如@derhass建议，调用 glClear 是重要的，特别是在启用深度测试的情况下（没有它，上次绘图调用的多维数据集将隐藏更新的多维数据集）。

i was trying to draw a cube, using the glDrawElements function, but even the simple code below only gives me a black screen. If helps, i'm programming on XCode 6.

//
//  main.cpp
//  Copyright (c) 2014 Guilherme Cardoso. All rights reserved.
//

#include <iostream>
#include <OpenGL/OpenGL.h>
#include <GLUT/GLUT.h>
#include <vector>
#include <math.h>

const GLfloat width = 500;
const GLfloat height = 500;

GLubyte cubeIndices[24] = {0,3,2,1,2,3,7,6
    ,0,4,7,3,1,2,6,5,4,5,6,7,0,1,5,4};

GLfloat vertices[][3] =
{{-1.0,-1.0,-1.0},{1.0,-1.0,-1.0},
    {1.0,1.0,-1.0}, {-1.0,1.0,-1.0}, {-1.0,-1.0,1.0},
    {1.0,-1.0,1.0}, {1.0,1.0,1.0}, {-1.0,1.0,1.0}};

GLfloat colors[][3] =
{{0.0,0.0,0.0},{1.0,0.0,0.0},
    {1.0,1.0,0.0}, {0.0,1.0,0.0}, {0.0,0.0,1.0},
    {1.0,0.0,1.0}, {1.0,1.0,1.0}, {0.0,1.0,1.0}};

void display(){
    glEnableClientState(GL_COLOR_ARRAY);
    glEnableClientState(GL_VERTEX_ARRAY);
    glColorPointer(3, GL_FLOAT, 0, colors);
    glVertexPointer(3, GL_FLOAT, 0, vertices);

    //glDrawArrays(GL_QUADS, 0, 24);
    glDrawElements(GL_QUADS, 24,GL_UNSIGNED_BYTE, cubeIndices);
    glDisableClientState(GL_VERTEX_ARRAY);
    glutSwapBuffers();
}

void mouse(int button, int state, int x, int y){

}

void keyboard(unsigned char key, int x, int y){
    if(key=='q' || key == 'Q') exit(0);
}

void init(){
    glEnable(GL_DEPTH_TEST);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0,width ,height, 0);
    glMatrixMode(GL_MODELVIEW);

    glClearColor (1.0, 1.0, 1.0,1.0);
    //glColor3f(0.0,0.0,0.0);
}

void idle(){

}

int main(int argc,  char **argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(width, height);
    glutCreateWindow("Assignment 3");
    glutPositionWindow(0, 0);


    glutDisplayFunc(display);
    glutMouseFunc(mouse);
    glutKeyboardFunc(keyboard);
    glutIdleFunc(idle);

    init();
    glutMainLoop();
}

i already checked some tutorials, and is no much different of what i'm doing.

解决方案

Actually your code is drawing the cube just fine. Look closely :P

The main issue is your projection. The initial GL viewing volume is a -1 to 1 cube, but the cube you're drawing is -1 to 1. The call to gluOrtho2D defines the projection in OpenGL coordinates, which you make the same as pixels, but since your cube is -1 to 1 it is only two pixels big, the rest being offscreen.

Instead, drop the gluOrtho2D, which sets the Z dimension -1 to 1 and only allows you to set X/Y, and create a slightly bigger projection...

glOrtho(-2, 2, -2, 2, -2, 2);

---

Note: As @derhass suggests, calling glClear is important especially with depth testing enabled (without it, the cube from the last draw call will hide the updated cube).

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