Can't bind a texture to a GL_QUADS

Question

I try to do an animation in OpenGL, my vertices and animations are working, but I would like to put a background image to it, with a file such as a bmp, or whatever.

So after a few reads I try the quads technique, which is simply to show a quad and bind a texture to it.

I use the STB_Image library, and it seems that I correctly point to my file (if I make mistakes on the filename I definitely got a much faster response from my program).

And I implemented a print to see if it catches the right file and it does!

My code look like this, and my result is a white square that appears in the correct coordinates, but no texture appears, the file is correctly loaded (with correct sizes printed), it just doesn't bind or appear on the square...

glClear(GL_COLOR_BUFFER_BIT);
glColor3f(1.0, 1.0, 1.0);

int width, height, nrChannels;
unsigned char* data = stbi_load("test.jpg", &width, &height, &nrChannels, 0);
if (data == NULL) {
    printf("Error in loading the image\n");
    exit(1);
}
printf("Loaded image with a width of %dpx, a height of %dpx and %d channels\n", width, height, nrChannels);
unsigned int texture;

glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glBegin(GL_QUADS);
glVertex2f(2.0, 1.0);
glTexCoord2f(2.0, 1.0);
glVertex2f(8.0, 1.0);
glTexCoord2f(8.0, 1.0);
glVertex2f(8.0, 7.0);
glTexCoord2f(8.0, 7.0);
glVertex2f(2.0, 7.0);
glTexCoord2f(2.0, 7.0);
glEnd();
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
if (data)
{
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
}
else
{
    std::cout << "Failed to load texture" << std::endl;
}

glDisable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, 0);

Any ideas?

Why are you setting the texture data *after* drawing the quad? — user253751, Jan 24 '20 at 13:44

Rabbid76 · Accepted Answer · 2020-01-24T13:41:52.660

glTexImage2D specify the two-dimensional texture image for the texture object. You have to do that the quad is drawn.
Furthermore 2 dimensional texturing has to be enabled by glEnable(GL_TEXTURE_2D). The texture coordinates have to be in range [0.0, 1.0] (See How do opengl texture coordinates work?).
glTexCoord2f has to be set before glVertex2f, because the current color, normal and texture coordinates are associated with the vertex when glVertex is called.
Since you don't generate mipmaps (glGenerateMipmap), the texture minifying function (GL_TEXTURE_MIN_FILTER) has to be set to GL_LINEAR or GL_NEAREST. Else the texture would be mipmap incomplete.

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_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
if (data)
{
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
}
else
{
    std::cout << "Failed to load texture" << std::endl;
}
glBindTexture(GL_TEXTURE_2D, 0);

glClear(GL_COLOR_BUFFER_BIT);

glBindTexture(GL_TEXTURE_2D, texture);
glEnable(GL_TEXTURE_2D);

glColor4f(1.0, 1.0, 1.0, 1.0);
glBegin(GL_QUADS);
glTexCoord2f(0.0, 1.0);
glVertex2f(2.0, 1.0);
glTexCoord2f(1.0, 1.0);
glVertex2f(8.0, 1.0);
glTexCoord2f(1.0, 0.0);
glVertex2f(8.0, 7.0);
glTexCoord2f(0.0, 0.0);
glVertex2f(2.0, 7.0);
glEnd();

glDisable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, 0);

glColor3f(1.0, 1.0, 1.0);

Thanks so much ! It works ! I will take a complete lecture about texture coordinates, thanks again ! — FortKnox, Jan 24 '20 at 17:52

Can't bind a texture to a GL_QUADS

1 Answers1