Distance to ()

Distance to ()
distance to ( v)
Category	Sensing
Type	Reporter
Introduced in	11Oct03 (0.x)

The Distance to () block is a Sensing block and a Reporter block. The block reports the Euclidean distance, in pixels, between it and the mouse-pointer or a specified sprite's costume center, even if the specified sprite is hidden.

The Scratch Cat saying its distance from the toad.

If there is nothing in the drop-down insert of the block, or if a sprite that was deleted is still in the drop-down insert, it reports the distance as 10,000. In v432 of Scratch 2.0 and earlier, it reported 0 instead, but this was changed in order to maintain compatibility with Scratch 1.4.

This block is case-sensitive.

Example Uses

As this block can give distances between objects, it is very useful in projects that require a great deal of careful sensing and movement.

Some common uses for the Distance to () block:

• Estimating when collisions will occur

if <(distance to (snowball v)) < (40)> then
say [Watch out!]
wait until <touching (snowball v)?>
say [] // stop saying the message
stop [all v]

• Helping determine how long it should take a sprite to move somewhere, judging from the distance

set [movements v] to ([ceiling v] of ((distance to (meteor v)) / (10))) // "movements" being the number of 10-pixel motions to reach the meteor

• Determining how far a rocket should fire

set [real distance v] to (join ((distance to (asteroid v)) * (10000)) [ kilometers]) // for relating pixel distance to real life

• Detecting distances from an invisible sprite and displaying the score as a game

change [score v] by ((1800) - ((10) * (distance to (bullseye v))))

• Making a variable change when you move the sprite around from another sprite

forever
set [safety v] to ((100) - ((distance to (house v)) / (3))

Workaround

Main article: List of Block Workarounds

This block can be replicated with the following code:

([sqrt v] of (((([x position v] of (Target Sprite v)) - (x position)) * (([x position v] of (Target Sprite v)) - (x position))) + ((([y position v] of (Target Sprite v)) - (y position)) * (([y position v] of (Target Sprite v)) - (y position))))

This can be visualized as a right-angled triangle. The Pythagorean theorem can be used to find the length of the hypotenuse.

Related Suggestion

Some Scratchers want a block that gives the distance to any location, not just a sprite. It would be like this:

(distance to x: () y: ():: sensing)

However, it can be replicated with a similar workaround:

([sqrt v] of ((((target x) - (x position)) * ((target x) - (x position))) + (((target y) - (y position)) * ((target y) - (y position)))))

Alternatively, a sprite can be moved to the wanted location:

//Inside sprite1:
broadcast (move v) and wait
set [result v] to (distance to (Move sprite v))

//Inside Move sprite:
when I receive [move v]
go to x: (target x) y: (target y)

Note:

If the sprite needs to move to an off-screen target position, see How to Go Off the Screen Edge.