sampler2DArray - setup and use - opengl

Question

I'm studying OpenGL and I had to use sampler2DArray. I am in torment all day long - all to no avail. I have two questions:
How to create a list of textures?
How to use sampler2DArray in the shader?
Here is the result of my attempts to create a list of textures:
// textures - ids loaded textures
private int createTextureArray(GL2 gl, int[] textures, int width, int height) {
int layerCount = textures.length;
int mipLevelCount = 1;
IntBuffer texture = IntBuffer.allocate(1);
gl.glGenTextures(1, texture);
gl.glActiveTexture(GL.GL_TEXTURE0);
gl.glBindTexture(GL2.GL_TEXTURE_2D_ARRAY, texture.get(0));
gl.glTexStorage3D(GL2.GL_TEXTURE_2D_ARRAY, mipLevelCount, GL2.GL_RGBA8, width, height, layerCount);
for (int i = 0; i<textures.length; i++) {
gl.glTexSubImage3D(GL2.GL_TEXTURE_2D_ARRAY, i, // error here
0, 0, 0,
width, height, layerCount,
GL2.GL_RGBA, GL2.GL_UNSIGNED_BYTE,
textures[i]);
}
// Always set reasonable texture parameters
gl.glTexParameteri(GL2.GL_TEXTURE_2D_ARRAY, GL2.GL_TEXTURE_MIN_FILTER, GL2.GL_LINEAR);
gl.glTexParameteri(GL2.GL_TEXTURE_2D_ARRAY, GL2.GL_TEXTURE_MAG_FILTER, GL2.GL_LINEAR);
gl.glTexParameteri(GL2.GL_TEXTURE_2D_ARRAY, GL2.GL_TEXTURE_WRAP_S, GL2.GL_CLAMP_TO_EDGE);
gl.glTexParameteri(GL2.GL_TEXTURE_2D_ARRAY, GL2.GL_TEXTURE_WRAP_T, GL2.GL_CLAMP_TO_EDGE);
return texture.get(0);
}
Shader example:
#version 130
uniform sampler2DArray textures;
varying vec2 UV;
...
void main() {
...
int layer = 0;
gl_FragColor = texture2DArray(textures, vec3(UV, layer));
}
I will be grateful for the help.

Answer 1

An array texture is not a "list of textures". An array texture is a single OpenGL texture, one which individually has a number of quasi-independent layers in it. While you may conceptually think of each layer of an array texture as a separate conceptual texture, in OpenGL (and GLSL), it is a single object.
Given this, the interface in your function is incorrect. It should return a single texture object, and it should take as a parameter, not an array of int (note: OpenGL objects are unsigned integers), but a single integer: the number of array layers to create in that texture.
How you use an array texture in GLSL is simple. Your uniform for the sampler uses an array-texture sampler type (for example sampler2DArray for 2D array textures). You bind the array texture to the same texture image unit that you specified as the binding for the sampler uniform (just as you would for a non-array 2D texture).
Your GLSL is missing one thing. There is no texture2DArray function. The correct function to use is just texture. The texture type in post-GL 3.0 is specified solely by the parameter, not by the name of the function anymore.

Answer 2

In addition to what #NicolBolas already said: There is a bunch of problems with the shader code, mostly due to functionality that has been deprecated in version 130:
There is no method texture2DArray in any standard glsl version. There has been one in the EXT_texture_array extension, but this has never been integrated since in glsl 130 all texture lookup functions (texture2D, texture3D, ...) have been replaced by a overloaded texture command. If you are targeting 130 without extensions, you should use texture(textures, vec3(UV, layer))
The varying keyword is deprecated in glsl 130 and should be replaced by in/out
gl_FragColor is deprecated and a user defined output (out) variable should be used.
You might want to have a look at Section 1.2.1 of the GLSL 130 Spec which describes the deprecations and how they should be handled. In general I would encourage everyone not to use 130 at all today unless there is a special reason for it. Better move to OpenGL 3.3+ Core Profile and GLSL 330+.