OpenGL GL_TEXTURE_CUBE_MAP no textures / black

Question

I want to do a simple CG task: draw a skymap cube with textures on the 6 sides. Read already a lot of tutorials, but there is some problem with the textures. All 6 sides of the cubes are completely black (but if I replace in the fragment shader the texture(..) call with a simple vec4(1.0f, ...), the walls will be colored, so it must be something with the textures).

So, here's an excerpt of what I'm doing:

void SkyCube::init() {
    mShader = new Shader("./Shader/skybox.vs", "./Shader/skybox.fs");

    // from: https://www.opengl.org/wiki/Common_Mistakes#Creating_a_Cubemap_Texture

    glEnable(GL_TEXTURE_CUBE_MAP);
    glGenTextures(1, &mTextureId);
    glBindTexture(GL_TEXTURE_CUBE_MAP, mTextureId);
    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);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_BASE_LEVEL, 0);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAX_LEVEL, 0);

    // now load the textures from TGA files and make them available to OpenGL
    TgaLoader * tgaLoader = new TgaLoader();
    string texturefilenames[] = {"back", "front", "bottom", "top", "left", "right"};
    int texturedefs[] = {GL_TEXTURE_CUBE_MAP_POSITIVE_X, GL_TEXTURE_CUBE_MAP_NEGATIVE_X,
        GL_TEXTURE_CUBE_MAP_POSITIVE_Y, GL_TEXTURE_CUBE_MAP_NEGATIVE_Y,
        GL_TEXTURE_CUBE_MAP_POSITIVE_Z, GL_TEXTURE_CUBE_MAP_NEGATIVE_Z};
    for (int i = 0; i < 6; i++) {
        tgaLoader->loadTga(mTextures[i], "data/skycube/" + texturefilenames[i] + ".tga");
        glTexImage2D(texturedefs[i], 0, GL_RGB, mTextures[i].width, mTextures[i].height,
                0, GL_BGR, GL_UNSIGNED_BYTE, mTextures[i].imageData);
    }
    delete tgaLoader;

    mVboSkyCube = this->generateSkyCubeVBO(vec3(-1.0f, -1.0f, -1.0f), vec3(1.0f, 1.0f, 1.0f));

    glDisable(GL_TEXTURE_CUBE_MAP);
}

The generateSkyCubeVBO method basically generates all the vertices and texture normalized coords:

VertexBufferObjectAttribs* SkyCube::generateSkyCubeVBO(const vec3 &mi, const vec3 &ma) {
    vector<vec3> vertices;
    vector<vec3> normals;
    vector<vec2> textureUV;
    // tofo liste mit texture koords
    // 00 01
    // 10 11
    // 2d vec

    vertices.push_back(vec3(mi.x, ma.y, mi.z));
    vertices.push_back(vec3(mi.x, ma.y, ma.z));
    vertices.push_back(vec3(ma.x, ma.y, ma.z));
    vertices.push_back(vec3(ma.x, ma.y, mi.z));

    normals.push_back(vec3(0.0f, 1.0f, 0.0f));
    normals.push_back(vec3(0.0f, 1.0f, 0.0f));
    normals.push_back(vec3(0.0f, 1.0f, 0.0f));
    normals.push_back(vec3(0.0f, 1.0f, 0.0f));

    textureUV.push_back(vec2(0.0f, 0.0f));
    textureUV.push_back(vec2(0.0f, 1.0f));
    textureUV.push_back(vec2(1.0f, 0.0f));
    textureUV.push_back(vec2(1.0f, 1.0f));


    vertices.push_back(vec3(mi.x, mi.y, mi.z));
    vertices.push_back(vec3(ma.x, mi.y, mi.z));
    vertices.push_back(vec3(ma.x, mi.y, ma.z));
    vertices.push_back(vec3(mi.x, mi.y, ma.z));

    normals.push_back(vec3(0.0f, -1.0f, 0.0f));
    normals.push_back(vec3(0.0f, -1.0f, 0.0f));
    normals.push_back(vec3(0.0f, -1.0f, 0.0f));
    normals.push_back(vec3(0.0f, -1.0f, 0.0f));

    textureUV.push_back(vec2(0.0f, 0.0f));
    textureUV.push_back(vec2(0.0f, 1.0f));
    textureUV.push_back(vec2(1.0f, 0.0f));
    textureUV.push_back(vec2(1.0f, 1.0f));


    vertices.push_back(vec3(mi.x, mi.y, mi.z));
    vertices.push_back(vec3(mi.x, ma.y, mi.z));
    vertices.push_back(vec3(ma.x, ma.y, mi.z));
    vertices.push_back(vec3(ma.x, mi.y, mi.z));

    normals.push_back(vec3(0.0f, 0.0f, -1.0f));
    normals.push_back(vec3(0.0f, 0.0f, -1.0f));
    normals.push_back(vec3(0.0f, 0.0f, -1.0f));
    normals.push_back(vec3(0.0f, 0.0f, -1.0f));

    textureUV.push_back(vec2(0.0f, 0.0f));
    textureUV.push_back(vec2(0.0f, 1.0f));
    textureUV.push_back(vec2(1.0f, 0.0f));
    textureUV.push_back(vec2(1.0f, 1.0f));


    vertices.push_back(vec3(mi.x, mi.y, ma.z));
    vertices.push_back(vec3(ma.x, mi.y, ma.z));
    vertices.push_back(vec3(ma.x, ma.y, ma.z));
    vertices.push_back(vec3(mi.x, ma.y, ma.z));

    normals.push_back(vec3(0.0f, 0.0f, 1.0f));
    normals.push_back(vec3(0.0f, 0.0f, 1.0f));
    normals.push_back(vec3(0.0f, 0.0f, 1.0f));
    normals.push_back(vec3(0.0f, 0.0f, 1.0f));

    textureUV.push_back(vec2(0.0f, 0.0f));
    textureUV.push_back(vec2(0.0f, 1.0f));
    textureUV.push_back(vec2(1.0f, 0.0f));
    textureUV.push_back(vec2(1.0f, 1.0f));


    vertices.push_back(vec3(mi.x, mi.y, mi.z));
    vertices.push_back(vec3(mi.x, mi.y, ma.z));
    vertices.push_back(vec3(mi.x, ma.y, ma.z));
    vertices.push_back(vec3(mi.x, ma.y, mi.z));

    normals.push_back(vec3(-1.0f, 0.0f, 0.0f));
    normals.push_back(vec3(-1.0f, 0.0f, 0.0f));
    normals.push_back(vec3(-1.0f, 0.0f, 0.0f));
    normals.push_back(vec3(-1.0f, 0.0f, 0.0f));

    textureUV.push_back(vec2(0.0f, 0.0f));
    textureUV.push_back(vec2(0.0f, 1.0f));
    textureUV.push_back(vec2(1.0f, 0.0f));
    textureUV.push_back(vec2(1.0f, 1.0f));


    vertices.push_back(vec3(ma.x, mi.y, mi.z));
    vertices.push_back(vec3(ma.x, ma.y, mi.z));
    vertices.push_back(vec3(ma.x, ma.y, ma.z));
    vertices.push_back(vec3(ma.x, mi.y, ma.z));

    normals.push_back(vec3(1.0f, 0.0f, 0.0f));
    normals.push_back(vec3(1.0f, 0.0f, 0.0f));
    normals.push_back(vec3(1.0f, 0.0f, 0.0f));
    normals.push_back(vec3(1.0f, 0.0f, 0.0f));

    textureUV.push_back(vec2(0.0f, 0.0f));
    textureUV.push_back(vec2(0.0f, 1.0f));
    textureUV.push_back(vec2(1.0f, 0.0f));
    textureUV.push_back(vec2(1.0f, 1.0f));


    GLuint nrVertices = vertices.size();
    VertexBufferObjectAttribs::DATA *attrData = new VertexBufferObjectAttribs::DATA[nrVertices];

    for (GLuint i = 0; i < nrVertices; ++i) {
        vec3 v = vertices[i];
        vec3 n = normals[i];
        vec2 t = textureUV[i];

        attrData[i].vx = v.x;
        attrData[i].vy = v.y;
        attrData[i].vz = v.z;
        attrData[i].vw = 1.0f;

        attrData[i].nx = n.x;
        attrData[i].ny = n.y;
        attrData[i].nz = n.z;
        attrData[i].nw = 0.0f;

        attrData[i].tx = t.x;
        attrData[i].ty = t.y;
        attrData[i].tz = 0.0f;
        attrData[i].tw = 0.0f;
    }

    VertexBufferObjectAttribs *vbo = new VertexBufferObjectAttribs();
    vbo->setData(attrData, GL_STATIC_DRAW, nrVertices, GL_QUADS);

    vbo->addAttrib(VERTEX_POSITION);
    vbo->addAttrib(VERTEX_NORMAL);
    vbo->addAttrib(VERTEX_COLOR);
    vbo->addAttrib(VERTEX_TEXTURE);
    vbo->bindAttribs();

    delete[] attrData;

    return vbo;
}

That works fine, all textures are successfully loaded. The vertex shader:

// OpenGL 3.3
#version 130

// following is probably not really needed
#define VERT_POSITION   0
#define VERT_NORMAL     1
#define VERT_COLOR  2
#define VERT_TEXTURE    3

uniform mat4x4 matModel;
uniform mat4x4 matView;
uniform mat4x4 matProjection;

attribute vec4 Position;
attribute vec4 Normal;
attribute vec4 Color;
attribute vec4 Texture;

out vec4 VertPosition;
out vec4 VertNormal;
out vec4 VertColor;
out vec4 VertTexture;

void main()
{      
    VertPosition = Position; 
    VertNormal   = Normal;
    VertColor    = Color;
    VertTexture  = Texture;

    gl_Position = matProjection * matView * matModel * vec4(Position.xyz, 1);
}

The fragment shader:

// OpenGL 3.3
#version 130

in vec4 VertPosition;
in vec4 VertNormal;
in vec4 VertColor;
in vec4 VertTexture; // Interpolated values from the vertex shaders, similar to the tutorial :-)

uniform vec3 lightPos;
uniform sampler2D skyBoxTextureSampler; // to know which texture to access, from the tutorial :-)

void main()
{
    vec4 color = VertColor;
    gl_FragColor = texture( skyBoxTextureSampler, VertTexture.xy);   //vec4( 1.0f, 1.0f, 0.9f, 1.0f); //
}

The render method:

void SkyCube::render(const Transform& trans) {
    mat4 projection = trans.projection;
    mat4 view = trans.view;
    mat4 model = mat4::identitiy();

    glPushAttrib(GL_ALL_ATTRIB_BITS);
    glPushClientAttrib(GL_CLIENT_ALL_ATTRIB_BITS);
    glEnable(GL_TEXTURE_CUBE_MAP);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_CUBE_MAP, mTextureId);

    mShader->bind();

    mShader->setMatrix("matProjection", projection, GL_TRUE);
    mShader->setMatrix("matView", view, GL_TRUE);
   // mShader->setMatrix("Texture")

    model = mat4::scale(20.0f, 20.0f, 20.0f);
    mShader->setMatrix("matModel", model, GL_TRUE);

    // set the texture
    mShader->seti("skyBoxTextureSampler", 0);


    mVboSkyCube->render();

    mShader->release();

    glPopClientAttrib();
    glPopAttrib();
}

The render method of the VBO object looks like this:

void VertexBufferObjectAttribs::render() {
    GLint size = m_attribLocations.size();
    glBindBuffer(GL_ARRAY_BUFFER, m_bufferId);
    for (GLint i = 0; i < size; ++i) {
        GLint attribLoc = m_attribLocations[i];
        glVertexAttribPointer(attribLoc, 4, GL_FLOAT, GL_FALSE, sizeof (DATA), ((GLchar*) NULL + 4 * sizeof (GLfloat) * i));
    }
    glBindBuffer(GL_ARRAY_BUFFER, 0);

    for (GLint i = 0; i < size; ++i)
        glEnableVertexAttribArray(m_attribLocations[i]);


    if (m_useIndexBuffer) {
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_indexBufferId);

        if (m_dynamicRendering) {
            glDrawElements(m_primitiveMode, m_nrDynamicIndices, GL_UNSIGNED_INT, 0);
        } else {
            glDrawElements(m_primitiveMode, m_nrIndices, GL_UNSIGNED_INT, 0);
        }
    } else {
        if (m_dynamicRendering) {
            glDrawArrays(m_primitiveMode, 0, m_nrDynamicVertices);
        } else {
            glDrawArrays(m_primitiveMode, 0, m_nrVertices);
        }
    }


    for (GLint i = 0; i < size; ++i)
        glDisableVertexAttribArray(m_attribLocations[i]);

}

If I compare this code with the steps from the tutorials, I cannot see anything missing or being in the wrong order.

Note that I cannot use a newer GLSL version as my current Linux version only supports 1.3.

Answer 1

Okay, so the answer - as already written in the comment above, is that the problem was that the shader contained a sampler2D, whereas instead it should have been using samplerCube. This is because in the C++ code I also was using the ...Cube functions correspondingly.