Problem to make an Orbit (circle with sin(x) and cos(x)) [SOLVED]

[nickelodeon0077]

i have an problem with the algorythm of make an circle with sin and cos
when i call this algorythm i have an spiral and not a circle
pls help

an example

Code: Select all

x = 100
y = 50
point = {x = 50, y = 50}

function foo()
	a = math.atan2(y-point.y, x-point.x)
	x = x + sin(a)
	y = y + cos(a)
end

[monkyyy]

Logic bug?

Floats don't follow indentity laws as the rounding errors stack up

If you want the distance to not change you can't really use addition and subtraction, try fixing the distance at the start of a step then scale the position after your logic

[monolifed]

formula is (x_0, y_0) + (R1 * sin(t), R2 *cos(t)) for t= 0 to 2* PI
and R1 = R2 for circle
it seems like you are updating your initial points in the function foo, you probably meant "x = point.x + sin(a)" ?

edit: I tried something random... rather than fixing it

Code: Select all

--#region
Vector2 = {}
Vector2.__index = vector2
function vector2(x, y)
  vec2 = {}
  setmetatable(Vector2, vec2)
  vec2.x = x
  vec2.y = y
  return vec2
end
--#endregion

-- sun
sunPos = vector2(0, 0)
sunGM = 100

--planet1
Planet1 = {R_min  = 50, R_max = 125, tilt = math.pi/3, phase = 0, orbit = vector2(50, 0)}
Planet1.color = {0.2, 1, 0.2, 1}
Planet1.pos = vector2(0, 0)
Planet1.angle = Planet1.phase

--planet2
Planet2 = {R_min  = 150, R_max = 100, tilt = math.pi/6, phase = 0, orbit = vector2(0, 40)}
Planet2.color = {1, 0.2, 0.2, 1}
Planet2.pos = vector2(0, 0)
Planet2.angle = Planet2.phase


function initPlanetPos(planet)
    local p = planet.phase
    
    local x = planet.orbit.x
    local y = planet.orbit.y
    
    local R = planet.R_max
    local r = planet.R_min

    planet.pos.x, planet.pos.y = x + R * math.cos(p), y + r * math.sin(p)
end

function updatePlanetPos(planet, dt)
    local a = planet.angle
    --local v = planet.velocity
    local R = planet.R_max
    local r = planet.R_min
    local d1 = planet.pos.x - sunPos.x
    local d2 = planet.pos.y - sunPos.y
    local d = math.sqrt(d1 * d1 + d2 * d2)
    local v = math.sqrt(sunGM * (2 / d - 1 / R))
    a = (a + v * dt) % (2 * math.pi)
    planet.angle = a
    planet.pos.x, planet.pos.y = planet.orbit.x + R * math.cos(a), planet.orbit.y + r * math.sin(a)
end

function love.load(arg)
  love.window.setTitle("Galaxy example 0.5")
  love.window.setMode(512, 512, {msaa = 16, vsync = true}) --if disable the vsync the spiral decreases the curve
  initPlanetPos(Planet1)
  initPlanetPos(Planet2)
end



function love.update(dt)
  if not paused then
    updatePlanetPos(Planet1, dt)
    updatePlanetPos(Planet2, dt)
  else
    --paused
  end
end

function love.draw()
  --if not paused then
  love.graphics.translate(256, 256)

  love.graphics.setColor(Planet1.color)
  
  love.graphics.rotate(-Planet1.tilt)
  love.graphics.ellipse( "line", Planet1.orbit.x, Planet1.orbit.y, Planet1.R_max, Planet1.R_min, 32 )
  love.graphics.rotate(Planet1.tilt)

  love.graphics.setColor(Planet2.color)
  
  love.graphics.rotate(-Planet2.tilt)
  love.graphics.ellipse( "line", Planet2.orbit.x, Planet2.orbit.y, Planet2.R_max, Planet2.R_min, 32 )
  love.graphics.rotate(Planet2.tilt)
  
  love.graphics.setColor(1, 0.7, 0, 1)
  love.graphics.circle("fill", sunPos.x, sunPos.y, 32)

  love.graphics.setColor(Planet1.color)

  love.graphics.rotate(-Planet1.tilt)
  love.graphics.circle("fill", Planet1.pos.x, Planet1.pos.y, 8)
  love.graphics.rotate(Planet1.tilt)

  love.graphics.setColor(Planet2.color)

  love.graphics.rotate(-Planet2.tilt)
  love.graphics.circle("fill", Planet2.pos.x, Planet2.pos.y, 8)
  love.graphics.rotate(Planet2.tilt)
  
  --else
    --paused
  --end
end

function love.keypressed(key, scancode, isrepeat)
  if key == "escape" then
    paused = not paused
  end
end

[nickelodeon0077]

formula is (x_0, y_0) + (R1 * sin(t), R2 *cos(t)) for t= 0 to 2* PI
and R1 = R2 for circle
it seems like you are updating your initial points in the function foo, you probably meant "x = point.x + sin(a)" ?

edit: I tried something random... rather than fixing it

man thnks with your code i understood better
anyway, what is the github link in the code

[monolifed]

Ignore it, it is a copy-paste error (I was searching through some github projects at the time)
I used the equation from the following page to calculate speed
https://en.wikipedia.org/wiki/Elliptic_orbit

[nickelodeon0077]

Ignore it, it is a copy-paste error (I was searching through some github projects at the time)
I used the equation from the following page to calculate speed
https://en.wikipedia.org/wiki/Elliptic_orbit

i'm imagineted