[SOLVED] Make an object follow another object.

[MarekkPie]

To add to the above: when you divide by the magnitude of the vector, you are "normalizing" it. Your original vector was

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{ magnitude * direction_of_x, magnitude * direction_of_y }

When you normalize it, you are doing this:

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{ magnitude * direction_of_x / magnitude, magnitude * direction_of_y / magnitude }

Therefore, you just end up with a vector simply pointing at the other object, rather than point and stretching to it. From there, you can add any speed you want, and it will be constant no matter how close you are to the other object.

[Chroteus]

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distance = sqrt(dx*dx+dy*dy)

Oh, I see. We use Pythagoras' Theorem to find out the distance. Thanks a lot. Now it *finally* struck me

[NathanGaming2005]

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function fish_move(dt)
	dx = (player.x - fish.x) * (fish.speed * dt)
	dy = (player.y - fish.y) * (fish.speed * dt)
	fish.x = fish.x + (dx * dt)
	fish.y = fish.y + (dy * dt)
end

I'd do it the same way, with two further modification.
First, you put in dt twice. You only need it once for each coordinate. So either remove it in the first two lines or in the second two lines.
Second, you probably noticed, that the fish is faster, if it is further away from the player. This is because, dx and dy both become larger, the larger the distance is.
Maybe this is what you want. If not, here is how to fix it. Divide the distance vector by its length:

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function fish_move(dt)
  dx = player.x - fish.x
  dy = player.y - fish.y
  distance = sqrt(dx*dx+dy*dy)
  fish.x = fish.x + (dx / distance * fish.speed * dt)
  fish.y = fish.y + (dy / distance * fish.speed * dt)
end

the sqrt don't working why?