OpenGL不绘图

Question

我使用GLFW作为OpenGL项目的GUI。我正在使用我的红皮书和测试代码，第一部分代码根本不起作用。我想说这是一个GLFW问题，因为我在JOGL中没有这个问题。

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

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

    if( !glfwOpenWindow( 300,300, 0,0,0,0,0,0, GLFW_WINDOW ) )
    {
        glfwTerminate();
        return 0;
    }

    while( running )
    {
        //GL Code here
        glClear(GL_COLOR_BUFFER_BIT);
        glClearColor(0.0, 0.0, 0.0, 0.0);

        glColor3f(1.0, 1.0, 1.0);
        glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
        glBegin(GL_POLYGON);
            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();


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

    glfwTerminate();

    return 0;
}

Answer 1

添加glLoadIdentity();修复了代码：

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

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
        glLoadIdentity();

        glClearColor(0.0, 0.0, 0.0, 0.0);
        glClearDepth(1.0);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        glColor3f(1.0, 1.0, 1.0);
        glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
        glBegin(GL_POLYGON);
            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();


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

    glfwTerminate();

    return 0;
}

Answer 2

你必须指定你希望glOrtho转换的矩阵

.....
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
......