Difference between revisions of "Math.distance"

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=== Description ===
 
=== Description ===
 
Returns the distance betwen two points.
 
Returns the distance betwen two points.
−
<source lang="lua">
+
<syntaxhighlight lang="lua">
 
(number) = math.distance(x1,y1,z1,x2,y2,z2)
 
(number) = math.distance(x1,y1,z1,x2,y2,z2)
 
(number) = math.distance({x1,y1,z1},{x2,y2,z2})
 
(number) = math.distance({x1,y1,z1},{x2,y2,z2})
 
(number) = math.distance({x=x1,y=y1,z=z1},{x=x2,y=y2,z=z2})
 
(number) = math.distance({x=x1,y=y1,z=z1},{x=x2,y=y2,z=z2})
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</source>
+
</syntaxhighlight>
  
 
'''Note''': the number will always be a positive number
 
'''Note''': the number will always be a positive number
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=== Example ===
 
=== Example ===
−
<source lang="lua">
+
<syntaxhighlight lang="lua">
 
local mydist = 256
 
local mydist = 256
 
function LevelX:onEnterFrame(e)
 
function LevelX:onEnterFrame(e)
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end
 
end
 
end
 
end
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</source>
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</syntaxhighlight>
 +
 
 +
=== '''Alternatives''' ===
 +
The math.distance may not be the fastest. Here are some tests:
 +
<syntaxhighlight lang="lua">
 +
-- simple function timer by @antix
 +
local x1, y1, x2, y2 = math.random(-100000, 100000), math.random(-100000, 100000), math.random(-100000, 100000), math.random(-100000, 100000)
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local dx, dy
 +
 
 +
-- init
 +
local dist = math.distance(x1, y1, x2, y2)
 +
print("*** POINT A: "..x1, y1, "POINT B: "..x2, y2)
 +
print("*** DISTANCE: "..dist)
 +
 
 +
-- tests
 +
local sqrt = math.sqrt
 +
 
 +
local data = {
 +
{
 +
"sqrt",
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function()
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dx, dy = x2-x1, y2-y1
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dist = sqrt(dx*dx + dy*dy)
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end, -- 56ms
 +
},
 +
{
 +
"exponent",
 +
function()
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dx, dy = x2-x1, y2-y1
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dist = (dx^2 + dy^2)^0.5
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end, -- 40ms
 +
},
 +
{
 +
"multiply/exponent",
 +
function()
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dx, dy = x2-x1, y2-y1
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dist = (dx*dx + dy*dy)^0.5
 +
end, -- 43ms
 +
},
 +
{
 +
"multiply/exponent without power",
 +
function()
 +
dx, dy = x2-x1, y2-y1
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dist = dx*dx + dy*dy
 +
end, -- 40ms but wrong result!
 +
},
 +
{
 +
"math.distance",
 +
function()
 +
dist = math.distance(x1, y1, x2, y2)
 +
end, -- 73ms
 +
},
 +
}
 +
 +
-- run all functions
 +
for i = 1, #data do
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local block = data[i]
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local func = block[2]
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local start = os.timer()
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for i = 1, 1000000 do -- 1 million repetitions!
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func()
 +
end
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local elapsed = math.floor((os.timer() - start) * 1000)
 +
print(block[1].." ("..elapsed.."ms)", "", "", "", "", "distance: "..dist)
 +
end
 +
 
 +
--[[ RESULTS
 +
*** POINT A: -95201 388 POINT B: -75997 76396
 +
*** DISTANCE: 78396.49022756057
 +
sqrt (56ms) distance: 78396.49022756057
 +
exponent (40ms) distance: 78396.49022756057
 +
multiply/exponent (43ms) distance: 78396.49022756057
 +
multiply/exponent without power (40ms) distance: 6146009680
 +
math.distance (73ms) distance: 78396.49022756057
 +
]]
 +
</syntaxhighlight>
  
 
{{Math}}
 
{{Math}}

Latest revision as of 20:54, 28 October 2024

Available since: Gideros 2020.9
Class: math

Description

Returns the distance betwen two points. 

(number) = math.distance(x1,y1,z1,x2,y2,z2)
(number) = math.distance({x1,y1,z1},{x2,y2,z2})
(number) = math.distance({x=x1,y=y1,z=z1},{x=x2,y=y2,z=z2})

Note: the number will always be a positive number

Parameters

x1: (number) X component of the first point
y1: (number) Y component of the first point
z1: (number) Z component of the first point optional
x2: (number) X component of the second point
y2: (number) Y component of the second point
z2: (number) Z component of the second point optional

Return values

Returns (number) the distance between the two points (always positive)

Example

local mydist = 256
function LevelX:onEnterFrame(e)
	-- player position
	posx, posy = self.player1.body:getPosition()
	-- for perfs
	for k, v in pairs(self.myobjects) do -- k=sprite, v=box2d body
		local x1, y1 = v:getPosition()
		if math.distance(x1, y1, posx, posy) > mydist then
			k:setVisible(false)
		else
			k:setVisible(true)
		end
	end
end

Alternatives

The math.distance may not be the fastest. Here are some tests: 

-- simple function timer by @antix
local x1, y1, x2, y2 = math.random(-100000, 100000), math.random(-100000, 100000), math.random(-100000, 100000), math.random(-100000, 100000)
local dx, dy

-- init
local dist = math.distance(x1, y1, x2, y2)
print("*** POINT A: "..x1, y1, "POINT B: "..x2, y2)
print("*** DISTANCE: "..dist)

-- tests
local sqrt = math.sqrt

local data = {
	{
		"sqrt",
		function()
			dx, dy = x2-x1, y2-y1
			dist = sqrt(dx*dx + dy*dy)
		end, -- 56ms
	},
	{
		"exponent",
		function()
			dx, dy = x2-x1, y2-y1
			dist = (dx^2 + dy^2)^0.5
		end, -- 40ms
	},
	{
		"multiply/exponent",
		function()
			dx, dy = x2-x1, y2-y1
			dist = (dx*dx + dy*dy)^0.5
		end, -- 43ms
	},
	{
		"multiply/exponent without power",
		function()
			dx, dy = x2-x1, y2-y1
			dist = dx*dx + dy*dy
		end, -- 40ms but wrong result!
	},
	{
		"math.distance",
		function()
			dist = math.distance(x1, y1, x2, y2)
		end, -- 73ms
	},
}
 
-- run all functions
for i = 1, #data do
	local block = data[i]
	local func = block[2]
	local start = os.timer()
	for i = 1, 1000000 do -- 1 million repetitions!
		func()
	end
	local elapsed = math.floor((os.timer() - start) * 1000)
	print(block[1].." ("..elapsed.."ms)", "", "", "", "", "distance: "..dist)
end

--[[ RESULTS
*** POINT A: -95201	388	POINT B: -75997	76396
*** DISTANCE: 78396.49022756057
sqrt (56ms)					distance: 78396.49022756057
exponent (40ms)					distance: 78396.49022756057
multiply/exponent (43ms)					distance: 78396.49022756057
multiply/exponent without power (40ms)					distance: 6146009680
math.distance (73ms)					distance: 78396.49022756057
]]



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