Opengl Texture rendering without color

Question

I am writing an openGl wrapper in rust for educational purposes. However, I have a problem displaying textures from an image file (jpg). The image is displayed as a grayscale image with some buggy red and green lines.

I am loading the image using the "image" crate and converting it to a ImageBuffer. The loading part is working, what i have checked by saving the image again.

I think that the conversion of the buffer to rgb is also working because the second time i save the image it is also working.

code to load the image:

extern  crate image;

use gl;

use std::{path, ffi::c_void};

#[derive(Debug)]
pub struct Texture {
    id: u32,
    location: gl::types::GLenum,
    path: path::PathBuf,
}

enum TextureError {
    FileNotFound(path::PathBuf),
    InvalidFileType(String)
}

impl Texture {
    pub fn new(file_path: &str, location: u32) -> Texture {
        let mut id = 0;

        let img = image::open(file_path).unwrap();
        img.save("res/test.jpg").unwrap();
        let img = match img {
            image::DynamicImage::ImageRgb8(img) => img,
            x => x.to_rgb8()
        };
        let width = img.width();
        let height = img.height();
        img.save("res/test2.jpg").unwrap();

        unsafe {
            gl::ActiveTexture(gl::TEXTURE0 + location);
            gl::GenTextures(1, &mut id);
            gl::BindTexture(gl::TEXTURE_2D, id);

            gl::TexParameteri(gl::TEXTURE_2D, gl::TEXTURE_WRAP_S, gl::REPEAT as i32);
            gl::TexParameteri(gl::TEXTURE_2D, gl::TEXTURE_WRAP_T, gl::REPEAT as i32);
            gl::TexParameteri(gl::TEXTURE_2D, gl::TEXTURE_MIN_FILTER, gl::LINEAR_MIPMAP_LINEAR as i32);
            gl::TexParameteri(gl::TEXTURE_2D, gl::TEXTURE_MAG_FILTER, gl::LINEAR as i32);

            gl::TexImage2D(gl::TEXTURE_2D, 0, gl::RGB8 as i32, width as i32, height as i32, 0, gl::RGB, gl::UNSIGNED_BYTE, (&img as &[u8]).as_ptr() as *const c_void);
            gl::GenerateMipmap(gl::TEXTURE_2D);
        }
        Texture {
            id,
            location,
            path: path::PathBuf::from(file_path)
        }
    }
}

main code:

The modules fundamental, shader, window, etc. are modules i wrote and tested. (they work as inteded)

extern crate gl;
extern crate glfw;

#[macro_use]
extern crate lazy_static;

mod fundamental;
mod shader;
mod window;

use window::Window;

use crate::fundamental::{Buffer, VertexArray, VertexAttribPtr, Texture};

fn main() {
    //setup glfw
    let mut window = Window::new();

    //load OpenGL
    gl::load_with(|s| window.glfw_window.get_proc_address(s) as *const _);
    unsafe {
        gl::Viewport(0, 0, 600, 600);
    }

    let vertices: Vec = vec![
        -0.5, -0.5, 0.0, 0.0, 0.0,
         0.5, -0.5, 0.0, 1.0, 0.0,
        -0.5, 0.5, 0.0, 0.0, 1.0,
         0.5, 0.5, 0.0, 1.0, 1.0
    ];
    
    let indices: Vec = vec![0, 1, 2, 1, 2, 3];

    let vao = VertexArray::new();
    vao.bind();
    let vbo = Buffer::new(gl::STATIC_DRAW, gl::ARRAY_BUFFER);
    let ebo = Buffer::new(gl::STATIC_DRAW, gl::ELEMENT_ARRAY_BUFFER);
    vbo.set_data(&vertices);
    ebo.set_data(&indices);
    let _v_a_ptr0 = VertexAttribPtr::new(0, 3, gl::FLOAT, 5 * 4, 0);
    let _v_a_ptr1 = VertexAttribPtr::new(1, 2, gl::FLOAT, 5 * 4, 3 * 4);
    vao.unbind();

    let shader = shader::Shader::new("shaders/shader.vs", "shaders/shader.fs", None);

    let _texture_bonfire = Texture::new("res/bonfire.jpg", 0);

    //rendering loop
    println!("---Starting rendering loop---");
    while window.not_closed() {
        window.poll_events();
        unsafe {
            gl::ClearColor(0.2, 0.3, 0.3, 1.0);
            gl::Clear(gl::COLOR_BUFFER_BIT);
            let mut error = gl::GetError();
            while error != 0 {
                println!("{}", error);
                error = gl::GetError();
            }
            shader.bind();
            vao.bind();
            gl::DrawElements(
                gl::TRIANGLES,
                indices.len() as i32,
                gl::UNSIGNED_INT,
                std::ptr::null(),
            );
        }
        window.swap_buffers();
    }
}

the code of the vertex_attrib_ptr moule:

(just in case it is needed)

use std::ffi::c_void;

pub struct VertexAttribPtr {
    location: u32,
}

impl VertexAttribPtr {
    pub fn new(
        location: u32,
        size_of_attribute: i32,
        vertex_type: gl::types::GLenum,
        vertex_size: i32,
        offset: u32,
    ) -> VertexAttribPtr {
        unsafe {
            gl::VertexAttribPointer(
                location,
                size_of_attribute,
                vertex_type,
                gl::FALSE,
                vertex_size,
                offset as *const c_void,
            );
            gl::EnableVertexAttribArray(location);
        }
        VertexAttribPtr { location }
    }

    #[allow(unused)]
    pub fn enable(&self) {
        unsafe {
            gl::EnableVertexAttribArray(self.location);
        }
    }

    #[allow(unused)]
    pub fn disable(&self) {
        unsafe {
            gl::DisableVertexAttribArray(self.location);
        }
    }
}

vertex shader

#version 460 core
layout (location = 0) in vec3 pos;
layout (location = 1) in vec2 tex_coord;

out vec2 texture_cord;

void main()
{
    gl_Position = vec4(pos.x, pos.y, pos.z, 1.0);
    texture_cord = tex_coord;
}

fragment shader

#version 460 core
out vec4 FragColor;

in vec2 texture_cord;

uniform sampler2D texture0;

void main()
{
    FragColor = texture(texture0, texture_cord);
    //FragColor = vec4(1.0);
}

rendered texture:

The texture image is also upside down, but this is a problem for later.

original image

Rabbid76 · Accepted Answer

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. Since the image has 3 color channels (gl::RGB), and is tightly packed the size of a row of the image may not be aligned to 4 bytes. When a RGB image with 3 color channels is loaded to a texture object and 3*width is not divisible by 4, gl::UNPACK_ALIGNMENT has to be set to 1, before specifying the texture image with gl::TexImage2D:

gl::PixelStorei(gl::UNPACK_ALIGNMENT, 1);
gl::TexImage2D(gl::TEXTURE_2D, 0, gl::RGB8 as i32, width as i32, height as i32, 0, gl::RGB, gl::UNSIGNED_BYTE, (&img as &[u8]).as_ptr() as *const c_void);

The texture is also flipped. You have to "swap" the 2nd component of the texture coordinates:

let vertices: Vec = vec![
   -0.5, -0.5, 0.0, 0.0, 1.0,
    0.5, -0.5, 0.0, 1.0, 1.0,
   -0.5,  0.5, 0.0, 0.0, 0.0,     
    0.5,  0.5, 0.0, 1.0, 0.0
];

Opengl Texture rendering without color

Answers (1)

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