Function to find these 4 points? (simple math problem)

[Eglaios]

I have a point A (x,y), and want to generate 4 points around, like this :

(A here is [0,0], but could have different coords)

I want to generate them from a for() loop into a table, so it would look like this :

Code: Select all

function genPoints(x,y) --Coords of A
 local points = {}
 local point = {}
 for i = 1, 4 do
  point.x, point.y = [?]
  point.otherData = [...]
  table.insert(points, point)
 end
 return points
end

Pretty sure it would be achievable using modulo and that kind of stuff, I'll still search, but if someone have an answer meanwhile, please share it, thanks!


Edit : I ended up with this :
point.x = x + (50*i-150)%100,
point.y = y + (50*i-100)%100,
...but the modulo automatically converts invert negative values... still searching...

[BrotSagtMist]

I dont see why you want a for loop for just 4 points here, that is just overcomplicating it.
Are you planning to add more points later?

[darkfrei]

Code: Select all

for i = 1, 4 do
  point.x, point.y = -50*math.cos(i*math.pi/2), 50*math.sin(i*math.pi/2)
  point.otherData = [...]
  table.insert(points, point)
 end

But positive y is bottom, not at the top.

[BrotSagtMist]

random pointnumbers:

Code: Select all

num=4 
len=50
for x=0, math.pi*2-0.01,math.pi*(2/num) do
 print(math.cos(x)*len,math.sin(x)*len) -- +point of origin
end

[darkfrei]

also

Code: Select all

for i, p in ipairs ({{x=1,y=0}, {x=0,y=1}, {x=-1,y=0}, {x=0,y=-1}}) do
	table.insert(points, {x=p.x*50, y=p.y*50})
end

[Eglaios]

Are you planning to add more points later?

These are particles, and the full loop looks like this :

Code: Select all

function particleEvent(x,y)
 for i=1, 4 do
  table.insert(particles,{
   posX = x + (50*i-150)%100,
   posY = y + (50*i-100)%100,
   particleData = ...,
   particleData2 = ...,
   etc.
  })
 end
end

I could simply have different lines for each of the 4 particles but it'd really look cleaner if I could manage to fit that into the loop itself...

I'll look at the answers and see if something works

[darkfrei]

I want to generate them from a for() loop into a table, so it would look like this :

Code: Select all

function genPoints(x,y) --Coords of A
 local points = {}
 local point = {} -- not in the loop
 for i = 1, 4 do
  point.x, point.y = [?]
  point.otherData = [...]
  table.insert(points, point)
 end
 return points
end

Please note that you insert here THE SAME POINT!

The point definition must be in the loop:

Code: Select all

function genPoints(x,y) --Coords of A
 local points = {}
 for i = 1, 4 do
  local point = {} -- in the loop
  point.x, point.y = [?]
  point.otherData = [...]
  table.insert(points, point)
 end
 return points
end

[Eglaios]

Code: Select all

for i = 1, 4 do
  point.x, point.y = -50*math.cos(i*math.pi/2), 50*math.sin(i*math.pi/2)
  point.otherData = [...]
  table.insert(points, point)
 end

Looks perfect for me! All the operations are written next to x and y without touching the loop

But positive y is bottom, not at the top.

I actually forgot to mention that my coordinates system is upside down :
It's basically a vertical-scrolling "climb-the-tower" game, so Y=0 is the floor, and it increases as it goes up

[BrotSagtMist]

I still dont get what you try to archieve here.
Writing a loop instead
points={x,y+50,x+50,y,x,y-50,x-50,y} ?
*scratches head*
There is nothing clean about this loop.

[milon]

I'd recommend either darkfrei or BrotSagtMist's approach to this. There's absolutely no benefit to using trig (sin/cos functions) unless you must - it's computationally expensive, less easy to maintain, etc.

Also, if you need to do a bunch of stuff with each particle, create a separate function to handle that. Then you just call that function 4 times - one for each point. Much cleaner!