OpenGL 2D textures not displaying properly c++

Question

I'm fairly new to OpenGL and have run into a problem that I can't seem to crack. I'm trying to add a simple 2D texture to a triangle, the texture seems to be loading fine but it's getting displayed grainy and in black and white.

texture

result

Here's my related code:

main.cxx

#include <iostream>
#include "display.h"
#include "shader.h"
#include "texture.h"
#include "mesh.h"
#include <glm/glm.hpp>
#include <GLFW/glfw3.h>

int main() 
{

    Display display(800, 600, "project2");

    Vertex vertices[] = {
        Vertex(glm::vec3(-0.5f, -0.5f, 0.0f), glm::vec2(0.0f, 0.0f)),
        Vertex(glm::vec3(0.5f, -0.5f, 0.0f), glm::vec2(1.0f, 0.0f)),
        Vertex(glm::vec3(0.0f, 0.5f, 0.0f), glm::vec2(0.5f, 1.0f)),
    };

    Mesh mesh(vertices, sizeof(vertices)/sizeof(vertices[0]));

    Shader shader("./shaders/shader");

    Texture texture("./textures/container.jpg");

    while (!display.IsClosed())
    {
        display.ProcessInput();

        display.Clear(0.0f, 0.15f, 0.3f, 1.0f);

        texture.Bind(0);
        shader.Bind();

        mesh.Draw();

        display.Update();
    } 

    return 0;
}

texture.cxx

#include "texture.h"

Texture::Texture(const std::string &filePath)
{
    int width, height, numComponents;
    unsigned char* imageData = stbi_load(filePath.c_str(), &width, &height, &numComponents, 4);

    if (!imageData) {
        std::cerr << "Failed to load texture: " << filePath << std::endl;
        return;
    }

    stbi_set_flip_vertically_on_load(true);

    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);

    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);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, imageData);
    glGenerateMipmap(GL_TEXTURE_2D);

    stbi_image_free(imageData);
}

Texture::~Texture()
{
    glDeleteTextures(1, &texture); 
}

void Texture::Bind(unsigned int unit)
{
    glActiveTexture(GL_TEXTURE0 + unit); 
    glBindTexture(GL_TEXTURE_2D, texture);
}

fragment shader

#version 330 core

out vec4 FragColor;
uniform sampler2D diffuse;
in vec2 texCoord0;

void main() {
    FragColor = texture(diffuse, texCoord0);
}

vertex shader

#version 330 core
layout (location=0) in vec3 position;
layout (location=1) in vec2 texCoord;

out vec2 texCoord0;

void main() {
    gl_Position = vec4(position, 1.0);
    texCoord0 = texCoord;
}

I had textures working before in another project and my code looks almost identical, if anyone could help me out that would be much appreciated.

Answer 1

When a RGB image with 3 color channels is loaded to a texture object, then GL_UNPACK_ALIGNMENT has to be set to 1:

glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB,
             GL_UNSIGNED_BYTE, imageData);

GL_UNPACK_ALIGNMENT specifies the alignment requirements for the start of each pixel row in memory. By default GL_UNPACK_ALIGNMENT is set to 4. This means the start of each line of the image is assumed to be aligned to an address which is a multiple of 4. Since the image data are tightly packed and each pixel has a size of 3 bytes, the alignment has to be changed.

To proper read the image the last parameter of stbi_load has to be 0 (since the jpg format provides 3 color channesl) or 3 (to force 3 color channels):

unsigned char* imageData = stbi_load(filePath.c_str(),
     &width, &height, &numComponents, 0);

---

stbi_load can be forced to generate an image with 4 color channels, by explicitly pass 4 to the last parameter:

See stb_image.h:

Basic usage (see HDR discussion below for HDR usage):
      int x,y,n;
      unsigned char *data = stbi_load(filename, &x, &y, &n, 0);
      // ... process data if not NULL ...
      // ... x = width, y = height, n = # 8-bit components per pixel ...

// ... replace '0' with '1'..'4' to force that many components per pixel

      // ... but 'n' will always be the number that it would have been if you said 0
      stbi_image_free(data)

In this case the format parameter has to be changed from GL_RGB to GL_RGBA when loading the image:

unsigned char* imageData = stbi_load(filePath.c_str(),
     &width, &height, &numComponents, 0);

// [...]

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGBA,
             GL_UNSIGNED_BYTE, imageData);