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If on Edge, Bounce (block)

If on Edge, Bounce
2.0 If On Edge, Bounce.png
Category Motion
Type Stack

The If on Edge, Bounce block is a Motion Block and a Stack Block. The block checks to see if its sprite is touching the edge of the screen with the move steps block — and if it is, the sprite will point in a direction that mirrors the direction from which it is coming. It uses a line perpendicular to the edge to determine the reflection angle.

Example Uses

  • Preventing a sprite from partially leaving the screen (often, this is followed by the Point in Direction block to stop reflection)
  • Reflection
  • Games such as "Pong"
  • Allowing sprites to bounce off the screen:
when gf clicked
if on edge, bounce
move (5) steps
  • It also works for games such as Fish.
turn cw (pick random (-10) to (10)) degrees
move (3) steps
if on edge, bounce
wait (0.01) secs


Main article: List of Block Workarounds

The If on Edge, Bounce block can be replicated with the following code, which uses some trigonometry:

if <touching [edge v]?> then
change x by (([sin v] of (direction)) * (-1))
if <touching [edge v]?> then
point in direction ((180) - (direction))
point in direction ((0) - (direction))
change x by ([sin v] of (direction))
  • This page was last modified on 25 March 2014, at 12:06.