"iba a comer" = "estaba comiendo"?

Question

I have been wondering that do these two different forms of Spanish grammar mean the same thing. For example "(yo) iba a comer" and "(yo) estaba comiendo". And what about the third form which - I think - is very close too, "(yo) estuve comiendo"

Answer 1

• Iba a comer justo cuando me llamaste. (no se sabe si al final empezó o no)

• Estaba comiendo cuando me llamaste. (ya había empezado. No se sabe si pudo terminar de comer o no)

• Estuve comiendo hasta las 3. (began to eat and finished eating at 3)

Answer 2

Thank you very much. Would you give also some examples? Because those always help a lot to understand difficult things.

Answer 3

"Iba a comer" is like "voy a comer", but in imperfect. It means that you were going to eat, and then... whatever. Since it is imperfect, you are watching the past action from inside, so you have to wait and see how it ends.
"Estaba comiendo" is in the imperfect too, but there is no "ir a + infinitivo". Here, you were in the middle of your meal, which had already started. The story is pictured from inside, as it happens.
"Estuve comiendo" contemplates the whole finished action from outside, after it is finished.