用C++ OpenGL和GLFW绘制一个简单的立方体

Question

用C++ OpenGL和GLFW绘制一个简单的立方体

c++openglglfw

7

所以，我正在尝试在openGL和GLFW中绘制一个简单的立方体。

在下面的代码中，我可以绘制立方体，但它只显示为一个简单的矩形。这里发生了什么？

我尝试了"glTransformf(0,0,-10);"，但如果我做任何小于-2的事情，那么立方体就会消失。在-2时，前面的面出现了。在默认位置0处，我可以看到立方体的背面。

此外，当我尝试旋转它时，只有一个矩形从窗口顶部移动到底部。看起来非常奇怪。

有人可以帮我找出程序为什么会这样表现吗？

#if defined(_WIN32) || defined(_WIN64)
#include <windows.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <fstream>

#define GLEW_STATIC
#include <GL/glew.h>
#include <GL/gl.h>
#include <GLFW/glfw3.h>

const char* gameTitle = "TEST";
GLFWwindow* window;

GLfloat vertices[] =
{
-1, -1, -1,   -1, -1,  1,   -1,  1,  1,   -1,  1, -1,
 1, -1, -1,    1, -1,  1,    1,  1,  1,    1,  1, -1,
-1, -1, -1,   -1, -1,  1,    1, -1,  1,    1, -1, -1,
-1,  1, -1,   -1,  1,  1,    1,  1,  1,    1,  1, -1,
-1, -1, -1,   -1,  1, -1,    1,  1, -1,    1, -1, -1,
-1, -1,  1,   -1,  1,  1,    1,  1,  1,    1, -1,  1
};

GLfloat colors[] =
{
0, 0, 0,   0, 0, 1,   0, 1, 1,   0, 1, 0,
1, 0, 0,   1, 0, 1,   1, 1, 1,   1, 1, 0,
0, 0, 0,   0, 0, 1,   1, 0, 1,   1, 0, 0,
0, 1, 0,   0, 1, 1,   1, 1, 1,   1, 1, 0,
0, 0, 0,   0, 1, 0,   1, 1, 0,   1, 0, 0,
0, 0, 1,   0, 1, 1,   1, 1, 1,   1, 0, 1
};

static void controls(GLFWwindow* window, int key, int scancode, int action, int mods)
{
if(action == GLFW_PRESS)
    if(key == GLFW_KEY_ESCAPE)
        glfwSetWindowShouldClose(window, GL_TRUE);
}

bool initWindow(const int resX, const int resY)
{
if(!glfwInit())
{
    fprintf(stderr, "Failed to initialize GLFW\n");
    return false;
}
glfwWindowHint(GLFW_SAMPLES, 4); // 4x antialiasing

// Open a window and create its OpenGL context
window = glfwCreateWindow(resX, resY, gameTitle, NULL, NULL);

if(window == NULL)
{
    fprintf(stderr, "Failed to open GLFW window.\n");
    glfwTerminate();
    return false;
}

glfwMakeContextCurrent(window);
glfwSetKeyCallback(window, controls);

// Get info of GPU and supported OpenGL version
printf("Renderer: %s\n", glGetString(GL_RENDERER));
printf("OpenGL version supported %s\n", glGetString(GL_VERSION));

glEnable(GL_DEPTH_TEST); // Depth Testing
glDepthFunc(GL_LEQUAL);
glDisable(GL_CULL_FACE);
glCullFace(GL_BACK);
return true;
}

static void drawCube()
{
static float alpha = 0;
glMatrixMode(GL_PROJECTION_MATRIX);
glLoadIdentity();
glTranslatef(0,0,-2);
glMatrixMode(GL_MODELVIEW_MATRIX);
//attempt to rotate cube
//glRotatef(alpha, 1, 0, 0);

/* We have a color array and a vertex array */
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, vertices);
glColorPointer(3, GL_FLOAT, 0, colors);

/* Send data : 24 vertices */
glDrawArrays(GL_QUADS, 0, 24);

/* Cleanup states */
glDisableClientState(GL_COLOR_ARRAY);
glDisableClientState(GL_VERTEX_ARRAY);
alpha += 0.1;
}

static void display()
{
glClearColor(0.0, 0.8, 0.3, 1.0);
while(!glfwWindowShouldClose(window))
{
    // Draw stuff
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    drawCube();

    // Update Screen
    //glFlush();
    glfwSwapBuffers(window);

    // Check for any input, or window movement
    glfwPollEvents();

    // Scale to window size
    GLint windowWidth, windowHeight;
    glfwGetWindowSize(window, &windowWidth, &windowHeight);
    glViewport(0, 0, windowWidth, windowHeight);
}
}

int main(int argc, char** argv)
{
if(initWindow(1024, 620))
{
    display();
}
printf("Goodbye!\n");
glfwDestroyWindow(window);
glfwTerminate();
return 0;
}

- user3707591

如果你感到好奇，你正在直接绘制到剪辑空间中，即一个以原点为中心的2x2x2立方体，如此描述：https://dev59.com/hX7aa4cB1Zd3GeqPwOff#23187139（这就是为什么你观察到的边缘在移出该视野体积时会“消失”的原因）。 - user755921

2个回答

5

我认为你的问题在于，你基本上是在使用正交投影，或者至少不是透视投影，而透视投影是能够给予立方体更多“3D”外观的。

尝试使用以下代码来设置正确的透视投影矩阵：

glMatrixMode(GL_PROJECTION_MATRIX);
glLoadIdentity();
gluPerspective(45, windowWidth / windowHeight, 0.1f, 100.0f);

// Draw calls.

- kevintodisco

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- genpfault · Accepted Answer

您从未设置（有意义的）投影矩阵。
不要滥用投影矩阵堆栈。
不要在drawCube()中设置您的矩阵，遵循单一职责原则等等。
在尝试绘制之前设置您的视口。
C++有C头文件的以c为前缀的版本（stdio.h -> cstdio），请使用它们。

#include <GL/glew.h>
#include <GLFW/glfw3.h>

#include <cstdio>

void controls(GLFWwindow* window, int key, int scancode, int action, int mods)
{
    if(action == GLFW_PRESS)
        if(key == GLFW_KEY_ESCAPE)
            glfwSetWindowShouldClose(window, GL_TRUE);
}

GLFWwindow* initWindow(const int resX, const int resY)
{
    if(!glfwInit())
    {
        fprintf(stderr, "Failed to initialize GLFW\n");
        return NULL;
    }
    glfwWindowHint(GLFW_SAMPLES, 4); // 4x antialiasing

    // Open a window and create its OpenGL context
    GLFWwindow* window = glfwCreateWindow(resX, resY, "TEST", NULL, NULL);

    if(window == NULL)
    {
        fprintf(stderr, "Failed to open GLFW window.\n");
        glfwTerminate();
        return NULL;
    }

    glfwMakeContextCurrent(window);
    glfwSetKeyCallback(window, controls);

    // Get info of GPU and supported OpenGL version
    printf("Renderer: %s\n", glGetString(GL_RENDERER));
    printf("OpenGL version supported %s\n", glGetString(GL_VERSION));

    glEnable(GL_DEPTH_TEST); // Depth Testing
    glDepthFunc(GL_LEQUAL);
    glDisable(GL_CULL_FACE);
    glCullFace(GL_BACK);
    return window;
}

void drawCube()
{
    GLfloat vertices[] =
    {
        -1, -1, -1,   -1, -1,  1,   -1,  1,  1,   -1,  1, -1,
        1, -1, -1,    1, -1,  1,    1,  1,  1,    1,  1, -1,
        -1, -1, -1,   -1, -1,  1,    1, -1,  1,    1, -1, -1,
        -1,  1, -1,   -1,  1,  1,    1,  1,  1,    1,  1, -1,
        -1, -1, -1,   -1,  1, -1,    1,  1, -1,    1, -1, -1,
        -1, -1,  1,   -1,  1,  1,    1,  1,  1,    1, -1,  1
    };

    GLfloat colors[] =
    {
        0, 0, 0,   0, 0, 1,   0, 1, 1,   0, 1, 0,
        1, 0, 0,   1, 0, 1,   1, 1, 1,   1, 1, 0,
        0, 0, 0,   0, 0, 1,   1, 0, 1,   1, 0, 0,
        0, 1, 0,   0, 1, 1,   1, 1, 1,   1, 1, 0,
        0, 0, 0,   0, 1, 0,   1, 1, 0,   1, 0, 0,
        0, 0, 1,   0, 1, 1,   1, 1, 1,   1, 0, 1
    };

    static float alpha = 0;
    //attempt to rotate cube
    glRotatef(alpha, 0, 1, 0);

    /* We have a color array and a vertex array */
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_COLOR_ARRAY);
    glVertexPointer(3, GL_FLOAT, 0, vertices);
    glColorPointer(3, GL_FLOAT, 0, colors);

    /* Send data : 24 vertices */
    glDrawArrays(GL_QUADS, 0, 24);

    /* Cleanup states */
    glDisableClientState(GL_COLOR_ARRAY);
    glDisableClientState(GL_VERTEX_ARRAY);
    alpha += 1;
}

void display( GLFWwindow* window )
{
    while(!glfwWindowShouldClose(window))
    {
        // Scale to window size
        GLint windowWidth, windowHeight;
        glfwGetWindowSize(window, &windowWidth, &windowHeight);
        glViewport(0, 0, windowWidth, windowHeight);

        // Draw stuff
        glClearColor(0.0, 0.8, 0.3, 1.0);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        glMatrixMode(GL_PROJECTION_MATRIX);
        glLoadIdentity();
        gluPerspective( 60, (double)windowWidth / (double)windowHeight, 0.1, 100 );

        glMatrixMode(GL_MODELVIEW_MATRIX);
        glTranslatef(0,0,-5);

        drawCube();

        // Update Screen
        glfwSwapBuffers(window);

        // Check for any input, or window movement
        glfwPollEvents();
    }
}

int main(int argc, char** argv)
{
    GLFWwindow* window = initWindow(1024, 620);
    if( NULL != window )
    {
        display( window );
    }
    glfwDestroyWindow(window);
    glfwTerminate();
    return 0;
}