What is the function of glActiveTexture and GL_TEXTURE0 in OpenGL?

Question

I'm finding a way to understand why glActiveTexture is needed. I have the code below:

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

If I imagine that the GL_TEXTURE_2D is a picture's frame hanging on the wall and textureId is the real picture, the glBindTexture is the only command for assigning a real picture to the frame, so, what are GL_TEXTURE0 and glActiveTexture?

Will my code below work fine?

glActiveTexture(GL_TEXTURE0); glGenTextures(1, &textureId); glBindTexture(GL_TEXTURE_2D, textureId);  glActiveTexture(GL_TEXTURE1); glTexImage2D(GL_TEXTURE_2D, .....) glTexParameteri(GL_TEXTURE_2D, ...) 

I'm currently working with OpenGL2.1.

Answer 1

If I imagine that the GL_TEXTURE_2D is a picture's frame hangging on the wall and textureId is the real picture,

Actually a very good analogy :)

so, what GL_TEXTURE0 and glActiveTexture are?

Think about a wall with multiple picture frames, the first frame being labeled GL_TEXTURE0, the second GL_TEXTURE1 and so on.