Texture isn't loading properly OpenGL

Question

I am using MS visual studio 2019 and just learning opengl in c++. I started learning from https://learnopengl.com and it showed many ways to load textures . I just used stb image for loading textures and here's the function for loading a texture :

 
static 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, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, 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 tried loading it in a rectangle but somehow it doesn't seem to print properly on it. I'm stuck for a couple of hours and still couldn't find what mistake I've made. here's the code for initializing the VAO and VBO:

    inline void InitTextureBuffer(const char* img_filepath)
    {
        texture_shader.Bind();
        tex_img_id = loadTexture(img_filepath);
        glGenVertexArrays(1, &tex_VAO);
        glGenBuffers(1, &tex_VBO);
        glBindVertexArray(tex_VAO);
        glBindBuffer(GL_ARRAY_BUFFER, tex_VBO);
        glBufferData(GL_ARRAY_BUFFER, sizeof(float) * 6 * 4, NULL, GL_DYNAMIC_DRAW);
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float), 0);
        glEnableVertexAttribArray(1);
        glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float), (void*)(2 * sizeof(float)));
        glBindBuffer(GL_ARRAY_BUFFER, 0);
        glBindVertexArray(0);
        texture_shader.Unbind();
    }

and function to draw the rect :

    inline void Draw_Rectangle_IMG(_Point _min, _Point _max)
    {
        glActiveTexture(GL_TEXTURE0);
        glBindVertexArray(tex_VAO);
        texture_shader.Bind();
        float vertices[] =
        {
             _min.x, _min.y,   0.0f, 0.0f ,
             _max.x, _min.y,   0.0f, 1.0f ,
             _max.x, _max.y,   1.0f, 1.0f ,

             _min.x, _min.y,   0.0f, 0.0f ,
             _max.x, _max.y,   1.0f, 1.0f ,
             _min.x, _max.y,   1.0f, 0.0f ,
        };
        glBindTexture(GL_TEXTURE_2D, tex_img_id);

        glBindBuffer(GL_ARRAY_BUFFER, tex_VBO);
        glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertices), vertices);
        glBindBuffer(GL_ARRAY_BUFFER, 0);
        glDrawArrays(GL_TRIANGLES, 0, 6);

        glBindVertexArray(0);
        glBindTexture(GL_TEXTURE_2D, 0);
        texture_shader.Unbind();
    }

the shaders I've used:

const std::string texture_shader_vs =
{
    "#version 330 core\n"
    "layout(location = 0) in vec2 aPos;\n"
    "layout(location = 1) in vec2 aTexCoord;\n"
    "\n"
    "out vec2 TexCoord;\n"
    "\n"
    "void main()\n"
    "{\n"
    "   gl_Position = vec4(aPos,0.0f, 1.0f);\n"
    "   TexCoord = aTexCoord;\n"
    "}\n"
};
const std::string texture_shader_fs =
{
    "#version 330 core\n"
    "out vec4 FragColor;\n"
    "\n"
    "in vec2 TexCoord;\n"
    "\n"
    "// texture sampler\n"
    "uniform sampler2D texture1;\n"
    "\n"
    "void main()\n"
    "{\n"
    "   FragColor = texture(texture1, TexCoord);\n"
    "}\n"
};

And the function where I did the calls:

    _Point p1, p2;
    p1 = _Point(-0.5f, -0.25f);
    p2 = _Point(0.5f, 0.25f);

    ogl.InitTextureBuffer("resources/textures/1.png");
    while (!glfwWindowShouldClose(ogl.GetWindow()))
    {
        glClear(GL_COLOR_BUFFER_BIT);

        ogl.Draw_Rectangle_IMG(p1, p2);

        glfwSwapBuffers(ogl.GetWindow());
        glfwPollEvents();
    }

The texture i tried to print is :

but the result I get is

I can't seem to find the error .Any help would be appreciated. Thanks!

@AlexF I tried changing vertices and it resulted in an access violation error in glGenerateMipmap(GL_TEXTURE_2D); — Shreeyash Shrestha
– Shreeyash Shrestha, Commented Jun 16, 2021 at 7:27
I would assume that the alignment of the image rows doesn't match the alignment of the texture image. I know that certain image file formats (like e.g. BMP) requires row alignment to multiples of 4. FYI: Texture upload and pixel reads — Scheff's Cat
– Scheff's Cat, Commented Jun 16, 2021 at 7:38

Rabbid76 · Accepted Answer · 2021-06-16 08:11:36Z

4

The association of the texture coordinates to the vertices is wrong. Change to:

float vertices[] =
{
    _min.x, _min.y,   0.0f, 1.0f,
    _max.x, _min.y,   1.0f, 1.0f,
    _max.x, _max.y,   1.0f, 0.0f,

    _min.x, _min.y,   0.0f, 1.0f,
    _max.x, _max.y,   1.0f, 0.0f,
    _min.x, _max.y,   0.0f, 0.0f,
};

By default OpenGL assumes that the start of each row of an image is aligned to 4 bytes.
This is because the GL_UNPACK_ALIGNMENT parameter by default is 4. When a RGB image with 3 color channels is loaded to a texture object and 3*width is not divisible by 4 this may cause a misalignment.

Change the alignment by setting the GL_UNPACK_ALIGNMENT to 1, before specifying the texture image with glTexImage2D:

glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);

When you remove glGenerateMipmap(GL_TEXTURE_2D);, then you have to change the minifying function (GL_TEXTURE_MIN_FILTER) as well. Since the filter is GL_LINEAR_MIPMAP_LINEAR, the texture would be "Mipmap Incomplete" if you do not change the minimize function to GL_NEAREST or GL_LINEAR.

edited Jun 16, 2021 at 8:11

answered Jun 16, 2021 at 7:34

Rabbid76

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1 Comment

Rabbid76 Over a year ago

@ShreeyashShrestha Do exactly what I've done in the answer. Use the texture coordinates (which I've changed right now) and glPixelStorei(GL_UNPACK_ALIGNMENT, 1);. (but change nothing else). I've tested the code and it works now fine for me.

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