Here's how to find the distance between 2 points

Tom2012

Had this in my folder of notes for a while and it's pretty useful.

The math is:

distance between = square root of distanceX² + distanceY²

In this example, the code is added to a bullet and hero is the main character.

-- Get distance between x points   self.dx = self:getX() - self.scene.hero:getX();   -- get distance between y points   self.dy = self:getY() - self.scene.hero:getY();   self.distance = math.sqrt((self.dx*self.dx)+(self.dy*self.dy))

techdojo

You can avoid the nasty (expensive) math.sqrt function by just pre-squaring the distance you want to check against,

so if you want to check if an object is within say 25 pixels instead of checking if self.distance <= 25, just set self.distance = ((self.dx * self.dx) + (self.dy * self.dy)) and then check if self.distance <= (25*25).

If you've got a lot of checks to do the savings will start to mount up.

Also - there used to be a quick hack in the old 8/16bit days where you could "guestimate" distance to +/-10% by calculating dx and dy as above and then simply using the max of dx or dy plus half the min of dx or dy, using a single bit shift right the "half" practically came for free.

Tom2012

Hey techdojo

That works perfectly. Thank you.

For anyone interested, here's my example:

(self.maxLength is the max length in this example)

-- Work out the distance from hero   self.dx = self:getX() - self.scene.hero:getX(); self.dy = self:getY() - self.scene.hero:getY();   self.distance = (self.dx*self.dx)+(self.dy*self.dy)   -- Distance went over maxLength   if(self.distance >= (self.maxLength*self.maxLength)) then   -- do something here   end

Teranth

@Tom2012 thanks for the share

talis

Thanks for the share guys:-)