How do I determine the direction of another sprite in Scratch

Question

I'm programming a simple game for education in MIT Scratch and want to make a sprite turn towards another sprite (think an alien ship following our hero ship). I can easily make the alien ship point towards the hero:

point towards 'hero'

But what I really want to do is something more gradual like this:

if alien direction (in degrees) > direction of hero: turn -2 degrees
if alien direction (in degrees) < direction of hero: turn 2 degrees

So how do I determine 'direction of hero'?

Answer 1

Unfortunately there doesn't seem to be a built-in way to get this, so some trigonometry is needed. To calculate the direction from sprite 1 to sprite 2 you can calculate the displacement from 1 to 2 in x and y, then use the atan function to find the required angle:

Since you actually want the direction relative to the direction the alien ship is facing, it might be better to use the vector product (aka cross product):

The screenshots here are taken from this Scratch project.

Answer 2

Use point towards as a way of finding out:

set temp to direction
point towards hero
if temp > direction
   set direction to temp-2
else if temp < direction
   set direction to temp-2
else
   set direction to temp