Question

为什么我无法使用此代码显示任何内容？

#include <iostream>
#include "GL/glfw.h"
#ifndef MAIN
#define MAIN
#include "GL/gl.h"
#include "GL/glu.h"
#endif
using namespace std;

void display();

int main()
{
    int running = GL_TRUE;
    glfwInit();

    if( !glfwOpenWindow( 640,480, 0,0,0,0,0,0, GLFW_WINDOW ) )
    {
        glfwTerminate();
        return 0;
    }

    while( running )
    {
        //GL Code here
        display();

        glfwSwapBuffers();
        // Check if ESC key was pressed or window was closed
        running = !glfwGetKey( GLFW_KEY_ESC ) &&
        glfwGetWindowParam( GLFW_OPENED );
    }

    glfwTerminate();

    return 0;
}

void display()
{
    glClearColor(0,0,0,0);
    glClear(GL_COLOR_BUFFER_BIT);
    glViewport(0,0,640,480);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    //glTranslatef(0, 0, -2);
    glBegin(GL_POLYGON);
        glColor3f(1.0, 0.2, 0.2);
        glVertex3f(0.25, 0.25, 0.0);
        glVertex3f(0.75, 0.25, 0.0);
        glVertex3f(0.75, 0.75, 0.0);
        glVertex3f(0.25, 0.75, 0.0);
    glEnd();
    glFlush();
}

Answer 1

我认为问题是当你没有指定坐标系时例如

void glOrtho(GLdouble   left,
             GLdouble   right,
             GLdouble   bottom,
             GLdouble   top,
             GLdouble   nearVal,
             GLdouble   farVal);

或

void glFrustum(GLdouble  left,
               GLdouble  right,
               GLdouble  bottom,
               GLdouble  top,
               GLdouble  nearVal,
               GLdouble  farVal);

默认坐标系是：

-1,1，-1,1，-1,1

所以glTranslate将对象移动到坐标系之外，openGL会剪切对象。

如果您将glTranslate（）调用更改为1.0，则该对象可见。

Answer 2

您尚未使用glViewport设置视口，也未设置投影矩阵。如果您将清晰颜色更改为黑色以外的颜色，您会在窗口中看到这种颜色吗？

尝试将代码更改为：

void display()
{
    glClearColor(0,0,0,0);
    glClear(GL_COLOR_BUFFER_BIT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(-1, 1, -1, 1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    //glTranslatef(0, 0, -2);
    glBegin(GL_POLYGON);
        glColor3f(1.0, 0.2, 0.2);
        glVertex3f(0.25, 0.25, 0.0);
        glVertex3f(0.75, 0.25, 0.0);
        glVertex3f(0.75, 0.75, 0.0);
        glVertex3f(0.25, 0.75, 0.0);
    glEnd();
    glFlush();
}

（创建OpenGL窗口时可能已正确设置视口，否则使用窗口宽度和高度初始化视图）

如果您的多边形有不正确的缠绕，{p <1}}

也会禁用背面剔除

OpenGL什么都不会显示

2 个答案: