C++ OpenGL, GLFW Drawing a simple cube

Question 1

C++ OpenGL, GLFW Drawing a simple cube

c++ opengl glfw

user3707591 · Jun 4, 2014 · Viewed 16.6k times · Source

Answer

Answer

You never set a (meaningful) projection matrix.
Abuse not the projection matrix stack.
Don't set your matrices in drawCube(), single responsibility principle and all that.
Set your viewport before trying to draw.
C++ has c-prefixed versions (stdio.h -> cstdio) of the C headers. Use those instead.

All together:

#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;
}

Question 2

So, I am trying to draw a simple cube in openGL and GLFW.

In the code below, I can draw the cube, but it just appears as a simple rectangle. what is happening here?

I've tried "glTransformf(0,0,-10);", but if I do anything less than -2, than the cube dissappears. at -2, the front face side appears. at the default position of 0, I can see the back side of the cube.

also, when I try to rotate it, all that shows up is a rectangle moving from the top of the window, to the bottom. Seems very odd.

Can anyone help me find out why the program is behaving this way?

#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;
}

C++ OpenGL, GLFW Drawing a simple cube

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