stb_image wont flip vertically when image loads for an opengl texture

Question

The image I am trying to load is turned 90 degrees when rendered. I am using "stbi flip image vertically on load" but when the texture is rendered, the image is turned 90 degrees.

I tried to change the index and tex coords, that didnt work.

//Mesh struct
Mesh mesh = {
// Position         // Color                // Tex coords
0.5f, 0.5f, 0.0f,   1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f,
0.5f, -0.5f, 0.0f,  0.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f,
-0.5f, -0.5f, 0.0f, 0.0f, 0.0f, 1.0f, 1.0f, 1.0f, 1.0f,
-0.5f, 0.5f, 0.0f,  0.0f, 0.0f, 0.5f, 1.0f, 0.0f, 1.0f,
// Index
0,1,2,2,3,0
};

//The other code
/*Texture*/
int width, height, bpp;
unsigned char* image;
string path = "res/textures/Brick.png";
unsigned int texture;

stbi_set_flip_vertically_on_load(1);
image = stbi_load(path.c_str(), &width, &height, &bpp, 4);

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

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_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);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_RGBA, 
GL_UNSIGNED_BYTE, image);

if (image)
    stbi_image_free(image);

glActiveTexture(GL_TEXTURE0);
glUniform1i(glGetUniformLocation(shader, "Texture"), 0);

/*Position*/
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 9 * sizeof(float), 
(void*)0);
glEnableVertexAttribArray(0);
/*Color*/
glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 9 * sizeof(float), 
(void*)(3 * sizeof(float)));
glEnableVertexAttribArray(1);
/*Texture*/
glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 9 * sizeof(float), 
(void*)(7 * sizeof(float)));
glEnableVertexAttribArray(2);

glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);

The texture should apear as the image and not rotated 90 degrees. Image: https://opengameart.org/sites/default/files/oga-textures/brick_base.png

If you want to flip the v coordinate, the simply swap the v coordinates of the attributes. In the last column of the initialization of `mesh` swap 0 and 1. — Rabbid76, Dec 26 '18 at 18:21

score 1 · Accepted Answer · edited Sep 06 '22 at 13:13

You said I tried to change the index and texture coordinates, that didn't work. but I think your problem is exactly in your 2D to 3D coordinate mapping.

90 degree rotation is expected with current mapped coordination you shared. I mean :

0.5f, 0.5f, 0.0f -> 0.0f, 0.0f
0.5f, -0.5f, 0.0f -> 1.0f, 0.0f
-0.5f, -0.5f, 0.0f -> 1.0f, 1.0f
-0.5f, 0.5f, 0.0f -> 0.0f, 1.0f

If you don't want the 90 degree rotation it should be :

0.5f, 0.5f, 0.0f -> 0.0f, 0.0f
0.5f, -0.5f, 0.0f -> 1.0f, 0.0f
-0.5f, -0.5f, 0.0f -> 0.0f, 1.0f
-0.5f, 0.5f, 0.0f -> 1.0f, 1.0f

So your mesh should be like this (didn't swap the colors, change it if you need):

    Mesh mesh = {
//  Position              Color               Texture coordinates
//  X      Y      Z       R     G     B       X     Y
    -0.5f, -0.5f, 0.0f,   1.0f, 0.0f, 0.0f,   0.0f, 0.0f,
    -0.5f, 0.5f,  0.0f,   0.0f, 1.0f, 0.0f,   0.0f, 1.0f,
    0.5f,  0.5f,  0.0f,   0.0f, 0.0f, 1.0f,   1.0f, 1.0f,
    0.5f,  -0.5f, 0.0f,   0.0f, 0.0f, 0.5f,   1.0f, 0.0f,
// Index
    0, 1, 2,
    2, 3, 0
    };

EDITED

The texture is rotated 45 degrees this time. Also the result of not include stbi flip vertically and not including it with the original and your mesh data is the same, so I feel as if the problem is actually in the rest of the code but idk what it is. — , Dec 26 '18 at 15:25
@BobTheTreeGod I edited the coordinates, hope this time works, I still believe your problem is in your coordinates. Tell me the results when you test it. — HMD, Dec 26 '18 at 15:36
@BobTheTreeGod *"The texture is rotated 45 degrees"* are you sure about that!? Note, a full circle has 360 degrees. — Rabbid76, Dec 26 '18 at 18:58

stb_image wont flip vertically when image loads for an opengl texture

1 Answers1