How to assign a texture to a single entry of a texture array?

Question

The C++ psuedo code to transmit the idea of what I want to do would be:

Texture_array tarr = Texture_array(6);
tarr[0] = texture;

Which I am attempting to do as follows:

    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glTexStorage3D(GL_TEXTURE_2D_ARRAY, 1, GL_RGBA8, 894, 894, 6);
    glTexSubImage3D(GL_TEXTURE_2D_ARRAY, 0, 0, 0, 0, 894, 894, 0, color_format, GL_UNSIGNED_BYTE, data);
    //Set the texture parameters of the image
    glTexParameteri(target, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(target, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(target, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(target, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

On the fragment shader I attempt to read the value as:

vec3 c = vec3(texture(text, vec3(f_uv.xy,0)));

However the end result is completely blak, despite data being an array of a valid texture (I have tested it and know data has been properly initialized, it works with normal textures, just not texture arrays)

Answer 1

glTexSubImage3D(GL_TEXTURE_2D_ARRAY, 0, 0, 0, 0, 894, 894, 0, color_format, GL_UNSIGNED_BYTE, data);

You're transmitting 3D data. But you told OpenGL that the 3D block of data has a depth of 0. So the number of pixels you're transmitting is... 0.

I have no idea why OpenGL doesn't provide an error when passing 0 for any of the sizing components (since that means you're not passing data). But that's your problem. You need to pass 1 for the depth if you're uploading a single 2D slice to the array.

Answer 2

The full explanation of what I was doing wrong is:

The depth parameter in the glTexSubimage3D refers to the depth of the data being sent. Since I am trying to send a single layer this depth should be 1 not 0 (the depth of an image/layer) (As explained by Nicol Bolas).

The zoffset parameter in the same function refers to the offset in layers where the data will be put inside the texture array.

In other words, following the array analogy, this is the value inside of the brackets.

The correct approach would thus be:

glTexSubImage3D(GL_TEXTURE_2D_ARRAY, 0, 0, 0, 2, 894, 894, 1, color_format, GL_UNSIGNED_BYTE, data);

Which in C++ pseudo code would be:

Texture_Array[2] = texture;