How to properly load an image to use as an OpenGL texture?

Question

I am trying to load an image into an OpenGL texture using SOIL2; however, it never seems to be correct unless I use SOIL2's load to texture function. I have tried using STB image and Devil, but both get similar results.

Code:

GLuint load_image(const std::string& path) {
    int iwidth, iheight, channels;
    unsigned char* image = SOIL_load_image(path.c_str(), &iwidth, &iheight, &channels, SOIL_LOAD_RGBA);
    //  std::cout << SOIL_last_result() << std::endl;
    //  float* image = stbi_loadf(path.c_str(), &iwidth, &iheight, &channels, STBI_rgb_alpha);
    //  if(!ilLoadImage(path.c_str()))
    //      std::cout << "Devil Failed to load image: " << iluErrorString(ilGetError()) << std::endl;
    //
    //  unsigned char* image = ilGetData();
    //
    //  int iwidth = ilGetInteger(IL_IMAGE_WIDTH);
    //  int iheight = ilGetInteger(IL_IMAGE_HEIGHT);
    //  int channels = ilGetInteger(IL_IMAGE_CHANNELS);

    GLuint texture;
    glGenTextures(1, &texture);

    glActiveTexture(GL_TEXTURE0 + texture);
    GLint old_unpack_alignment;
    glGetIntegerv(GL_UNPACK_ALIGNMENT, &old_unpack_alignment);
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

    glBindTexture(GL_TEXTURE_2D, texture);
    glCheckError();

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glCheckError();

    GLenum original_format = (channels == 4 ? GL_RGBA : GL_RGB);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, image);
    glGenerateMipmap(GL_TEXTURE_2D);

    glPixelStorei(GL_UNPACK_ALIGNMENT, old_unpack_alignment);
    return texture;
}

Screenshot:

What I should get:

I would like to know how to properly load an image into a texture.

Why are you calculating original_format and then not using it? — genpfault
– genpfault, Commented Jan 21, 2018 at 6:56

Francis Cugler · Accepted Answer · 2018-01-21 19:31:28Z

Here is an example of what my texture loading function looks like:

unsigned int loadTexture(char const * path)
{
    unsigned int textureID;
    glGenTextures(1, &textureID);

    int width, height, nrComponents;
    unsigned char *data = stbi_load(path, &width, &height, &nrComponents, 0);
    if (data)
    {
        GLenum format;
        if (nrComponents == 1)
            format = GL_RED;
        else if (nrComponents == 3)
            format = GL_RGB;
        else if (nrComponents == 4)
            format = GL_RGBA;

        glBindTexture(GL_TEXTURE_2D, textureID);
        glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, format == GL_RGBA ? GL_CLAMP_TO_EDGE : GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, format == GL_RGBA ? GL_CLAMP_TO_EDGE : GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

        stbi_image_free(data);
    }
    else
    {
        std::cout << "Texture failed to load at path: " << path << std::endl;
        stbi_image_free(data);
    }

    return textureID
}

I will usually set up my VAO & VBO before hand, then I'll use this to load in a texture. After this I'll configure my shader(s) for use, then within the render loop is where I'll use my shader, set the matrices passing in any of the needed uniforms, then after all the "model" information is completed I'll finally bind the VertexArrays, set the approrpriate texture to Active, then Bind those Texture(s) and fish up with drawing the arrays or primitives.

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