Using the < > and > < custom Gideros operators.

SinisterSoft · September 2017

The Gideros version of Lua has some extra operators not present in regular Lua.

Two of them are <> and >< (remember these are custom to Gideros Lua)

<> is used to compare two numbers and return the greater of them
>< is used to compare two numbers and return the lesser of them

You may not think so initially, but these are two really handy operators and can save your game both a lot of code and cpu time.

eg:

Instead of this:

pos=10
function gameLoop(e)
   x=x-1
   if x<5 then x=5 end
   print(x)
.
.

You can put this:

pos=10
function gameLoop(e)
   x=(x-1)<>5
   print(x)
.
.

Both of these routines will produce:

9
8
7
6
5
5
5 and so on...

To limit a number going up just use the other operator:

pos=10
function gameLoop(e)
   x=(x+1)><15
   print(x)
.
.

This will produce:

11
12
13
14
15
15
15 and so on...

hgy29 · September 2017

When I need to ensure a value is within ttwo specific bounds (for exemple when positionning my scene so that the player is visible without showing blank spaces if the player goes to the corner of the scene), I use:

 x=(x<>min)><max

SinisterSoft · September 2017

Furthering @hgy29 's very nice example - This is showing something you may do in your game:

dir=-1
x=10
min=5
max=15
function gameLoop(e)
	x=x+dir
	if x<min then
		x=min
	elseif x>max then
		x=max
	end
	print(x)

Can be turned into...

dir=-1
x=10
min=5
max=15
function gameLoop(e)
	x=((x+dir)<>min)><max
	print(x)

SinisterSoft · September 2017

Here is another example to always return the negative of a number:

x=10
function gameLoop(e)
	x=-x><x
	print(x)

And another to always return the positive of a number:

x=-10
function gameLoop(e)
	x=-x<>x
	print(x)

This should be faster than

x=math.abs(x)

or

if x<0 then x=-x end

But I haven't done any speed check to make sure.

hgy29 · September 2017

Nice tip for abs() replacement!

SinisterSoft · September 2017

I don't know if Lua (internally) does any caching of variables for the result, left or right sides. It would be good if it did - or maybe I could add a check for this in the comparison. Searching though tables for variables must be the thing that slows things down the most.

snooks · September 2017

Interesting additions... incidentally, are the Gideros Lua extensions documented in one place anywhere? If not, what are they all?

SinisterSoft · September 2017

to find the greater
a <> b

to find the lesser
a >< b

to convert from degrees to radian
^< a

to convert from radians to degrees
^> a

bitwise operators
a|b bor
a&b and
~a not
a~b xor
a<<b shift a left by b bits
a>>b shift a right by b bits
a//b integer divide use instead of floor(a/b)

macros
pi@3.142 set pi to 3.142 - isn't a variable so it acts like a constant

also the saving/loading of lua byte code is universal between different processor word sizes - eg 32 and 64 bit - unlike regular Lua.

snooks · September 2017

Cool, thanks.

SinisterSoft · September 2017

Don't forget that x=-x<>x should also be faster than math.abs(x) or if x<0 then x=-x end

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