Can't render Skybox in OpenGL

Question

There's no visible skybox, but the code seems to be working correctly.

That's what I finally see:

screen

I'm new to OpenGL, so this may be a problem in the binding or position of the code for GL. For full code you can visit: https://github.com/ZigoRiloo96/Riloo_Engine

Here I have class Skybox:

class Skybox
{
public:
    Skybox();
    ~Skybox();

    void Draw(const glm::mat4& view, const glm::mat4& projection);

private:
    unsigned int cubemapTexture;

    GLuint VAO;
    GLuint VBO;

    Shader* shader;

    GLuint loadCubemap(std::vector<std::string> faces);
};

Shaders:

#version 330 core
layout (location = 0) in vec3 aPos;

out vec3 TexCoords;

uniform mat4 projection;
uniform mat4 view;

void main()
{
    TexCoords = aPos;
    vec4 pos = projection * view * vec4(aPos, 1.0);
    gl_Position = pos.xyww;
}

#version 330 core
out vec4 FragColor;

in vec3 TexCoords;

uniform samplerCube skybox;

void main()
{    
    FragColor = texture(skybox, TexCoords);
}

And class realization:

Skybox::Skybox()
{
    GLfloat skyboxVertices[108] = 
    {
        // positions          
        -1.0f,  1.0f, -1.0f,
        -1.0f, -1.0f, -1.0f,
        1.0f, -1.0f, -1.0f,
        1.0f, -1.0f, -1.0f,
        1.0f,  1.0f, -1.0f,
        -1.0f,  1.0f, -1.0f,

        -1.0f, -1.0f,  1.0f,
        -1.0f, -1.0f, -1.0f,
        -1.0f,  1.0f, -1.0f,
        -1.0f,  1.0f, -1.0f,
        -1.0f,  1.0f,  1.0f,
        -1.0f, -1.0f,  1.0f,

        1.0f, -1.0f, -1.0f,
        1.0f, -1.0f,  1.0f,
        1.0f,  1.0f,  1.0f,
        1.0f,  1.0f,  1.0f,
        1.0f,  1.0f, -1.0f,
        1.0f, -1.0f, -1.0f,

        -1.0f, -1.0f,  1.0f,
        -1.0f,  1.0f,  1.0f,
        1.0f,  1.0f,  1.0f,
        1.0f,  1.0f,  1.0f,
        1.0f, -1.0f,  1.0f,
        -1.0f, -1.0f,  1.0f,

        -1.0f,  1.0f, -1.0f,
        1.0f,  1.0f, -1.0f,
        1.0f,  1.0f,  1.0f,
        1.0f,  1.0f,  1.0f,
        -1.0f,  1.0f,  1.0f,
        -1.0f,  1.0f, -1.0f,

        -1.0f, -1.0f, -1.0f,
        -1.0f, -1.0f,  1.0f,
        1.0f, -1.0f, -1.0f,
        1.0f, -1.0f, -1.0f,
        -1.0f, -1.0f,  1.0f,
        1.0f, -1.0f,  1.0f
    };

    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glBindVertexArray(VAO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(skyboxVertices), &skyboxVertices, GL_STATIC_DRAW);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);

    std::vector<std::string> faces
    {
        "Resources/skybox/right.jpg",
        "Resources/skybox/left.jpg",
        "Resources/skybox/top.jpg",
        "Resources/skybox/bottom.jpg",
        "Resources/skybox/front.jpg",
        "Resources/skybox/back.jpg"
    };

    cubemapTexture = loadCubemap(faces);

    shader = new Shader("Resources/Shaders/skybox.vp", "Resources/Shaders/skybox.frag");

    shader->Use();
    shader->setInt("skybox", 0);
}

Skybox::~Skybox()
{
}

void Skybox::Draw(const glm::mat4& view, const glm::mat4& projection)
{
    glDepthFunc(GL_LEQUAL);
    shader->Use();
    shader->setMat4("view", glm::mat4(glm::mat3(view)));
    shader->setMat4("projection", projection);
    // skybox cube
    glBindVertexArray(VAO);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_CUBE_MAP, cubemapTexture);
    glDrawArrays(GL_TRIANGLES, 0, 36);
    glBindVertexArray(0);
    glDepthFunc(GL_LESS); 
}

GLuint Skybox::loadCubemap(std::vector<std::string> faces)
{
    unsigned int textureID;
    glGenTextures(1, &textureID);
    glBindTexture(GL_TEXTURE_CUBE_MAP, textureID);

    int width, height, nrChannels;
    for (unsigned int i = 0; i < faces.size(); i++)
    {
        unsigned char *data = stbi_load(faces[i].c_str(), &width, &height, &nrChannels, 0);
        if (data)
        {
            glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
            stbi_image_free(data);
        }
        else
        {
            printf("Stb can't load this sh*t: %s\n", faces[i].c_str());
            stbi_image_free(data);
        }
    }
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);

    return textureID;
}

Make sure that a) you can render a simple polygon so that it is visible b) the skybox is facing you, i.e. it is not showing outside b) you are actually inside the skybox — Yunnosch, Mar 06 '18 at 05:57
Above includes the basic global method for solving any problem: https://ericlippert.com/2014/03/21/find-a-simpler-problem/ — Yunnosch, Mar 06 '18 at 05:59
I removed the C tag, if you reinsert it please make sure to calrify what is C about this question. And, if it is obvious to most readers, sorry. — Yunnosch, Mar 06 '18 at 06:04
see [swift sphere combine star data](https://stackoverflow.com/a/40171880/2521214) it use old style gl but that is not important. Yunnosch is right you have either wrong matrices or wrong winding rule. try to render your skybox geometry without textures it might be out of your frustrum (too far or near) , or behind camera. Also try `glDisable(GL_CULL_FACE);`. — Spektre, Mar 06 '18 at 09:22
It might also be that your near clipping plane (see projection matrix) is too close. It should be at most 1 as the sky box has a radius of 1. — Nico Schertler, Mar 06 '18 at 09:39
also zfar should be `>=sqrt(3)` or else the corners of 1x1x1 cube would cut off the frustrum — Spektre, Mar 07 '18 at 07:13

score 2 · Answer 1 · edited Mar 08 '18 at 07:44

Thanks to everyone for their help, but I made a silly mistake. After I rendered the skybox on an ordinary cube, I understood what the problem is. That is my function to set the matrices to shader (there he is, this scoundrel):

void Shader::setMat4(const char* char_s, const glm::mat4& mat)
{
    glUniformMatrix4fv(glGetUniformLocation(Program, "projection"), 1, GL_FALSE, glm::value_ptr(mat));
}

And solution is to replace "projection" with char_s.

Can't render Skybox in OpenGL

1 Answers1