OpenGL texture element Texture Target Understanding Glactivetexture glbindtexture

It can be simply understood as: There are n texture units in the graphics card (the number depends on your graphics card capabilities), each texture unit (GL_TEXTURE0, GL_TEXTURE1, etc.) have gl_texture_1d, gl_texture_2d, and so on, the following code:

struct Textureunit
{
    gluint targettexture1d;
    Gluint targettexture2d;
    Gluint Targettexture3d;
    Gluint Targettexturecube;
    ...
};
 
Textureunit Textureunits[gl_max_texture_image_units]
gluint currenttextureunit = 0;

By default, the currently active texture unit is 0.

void Glactivetexture (Glenum textureunit)
{
    currenttextureunit = textureunit  -gl_texture0;
}

Instead of activating the texture unit, Glactivetextue selects the currently active texture cell.

void Glbindtexture (Glenum texturetarget, Gluint textureobject)
{
    Textureunit *texunit = &textureunits[ Currenttextureunit];
    Switch (texturetarget)
    {case
    gl_texture_1d:texunit->targettexture1d = textureobject;
    Case gl_texture_2d:texunit->targettexture2d = Textureobject; break;
    Case Gl_texture_3d:texunit->targettexture3d = Textureobject; break;
    Case gl_texture_cubemap:texunit->targettexturecube = Textureobject; break;
    }
}

As you can see from the sample code: When you bind a texture target, it is the currently active texture cell.