Games [Performance] Use (inlined) DistanceSquared to compare distances

[wonder]

Variables:

'pX: Point X-coordinate
'pY: Point Y-coordinate
'cX: Circle center X-coordinate
'cY: Circle center Y-coordinate
'cR: Circle Radius

Bad:

'- Function calls are expensive. We have 2: Power() and Sqrt()
'- The Power() function itself is more expensive than simple multiplication (see why below)
'- The Sqrt() function itself is an iterative function that should always be avoided.
Sub isPointInCircle(pX As Double, pY As Double, cX As Double, cY As Double, cR As Double) As Boolean
    Return Sqrt(Power(cX - pX, 2) + Power(cY - pY, 2)) <= cR
End

Good:

'- No function calls
'- No Sqrt()
'- No Power()
Sub isPointInCircle(pX As Double, pY As Double, cX As Double, cY As Double, cR As Double) As Boolean
    '----------------------------------------
    'DistanceSquared = (dX * dX) + (dY * dY)
    'RadiusSquared   = (cR * cR)
    'Return DistanceSquared < RadiusSquared
    '----------------------------------------
    Dim dX = cX - pX As Double
    Dim dY = cY - pY As Double
    Return (dX * dX) + (dY * dY) <= (cR * cR)
End

'Note that I commented DistanceSquare and RadiusSquared,
'instead of declaring them as variables or function calls.

Now, let's have a look at the junk we just got rid of:

Power() function algorithm in Java:

Sqrt() function algorithm in Java:

Happy coding!

 

[sorex]

what's the use of <= in this line?

Return Sqrt(Power(cX - pX, 2) + Power(cY - pY, 2)) <= cR

 

[wonder]

@sorex, it allows the (Boolean) function to return whether or nor the distance is less or equal than the radius (as either True or False).
Using an IF statement to return a boolean which stems from a binary decision ("either this or that"), is in my opinion, very amateurish.

Ugly:

If a > b Then
    Return True
Else
    Return False
End If

Pretty:

Return a > b

 

[sorex]

sweet

Using an IF statement to return a boolean which stems from a binary decision ("either this or that"), is very amateurish.

I know someone who would answer "it reads easier"