Can anyone spot the obvious bug with this math (trig)?

Tom2012

Hey everyone. Got what should be a simple problem but I'm pulling out my hair as to why I'm getting the results I am.

A character walks at an angle to a point on the screen:

local nextX = self.scene.path[self.id].vertices.x[self.pathCounter]
local nextY = self.scene.path[self.id].vertices.y[self.pathCounter]

I'm using 'distance' to stop him when he gets with a range.

But he never actually gets there. Instead, there is always a distance of around 16 pixels.

Any help very much appreciated.

function CreeperBug:onEnterFrame()   local currentX,currentY = self:getPosition()   local nextX = self.scene.path[self.id].vertices.x[self.pathCounter] local nextY = self.scene.path[self.id].vertices.y[self.pathCounter]   local xDiff = nextX - currentX local yDiff = nextY - currentY   local distance = math.sqrt((xDiff*xDiff)+(yDiff*yDiff))   local angle = math.deg(math.atan2(yDiff,xDiff))   local nextX = currentX + (math.cos(angle) * 1) local nextY = currentY + (math.sin(angle) * 1)   if(self.phase == "walk") then self:setPosition(nextX, nextY) end   end

ar2rsawseen

@Tom2012
my most common mistake is forgetting that Gideros has Cartesian coordinate system, thus y axis is always inverted

Other usual problem is that some math function might work not from the 0 to 360 degrees as expected, but for example from -180 to 180 degrees.

This is my usual way on getting angle:

local angle = math.acos(yDiff/distance) if(xDiff >0) then angle = -angle end

Bill5567

Distance between 2 points

local x1, y1 = 100, 100
local x2, y2 = 200, 200

local distanceBetween = math.ceil(math.sqrt( ((y1-y2) ^ 2) + ((x1-x2) ^ 2) ))

Tom2012

Thanks guys, still having problems with this (tried both suggestions)

Here's a simple code that produces the problem I have:

local apple = Bitmap.new(Texture.new("apple.png")) apple:setAnchorPoint(0,0) stage:addChild(apple)   local pumpkin = Bitmap.new(Texture.new("pumpkin.png")) pumpkin:setAnchorPoint(0,0) stage:addChild(pumpkin) pumpkin:setPosition(100,100)   local angle = 45 local speed = 5   local x1, y1 = apple:getPosition() local x2, y2 = pumpkin:getPosition()   local nextX = x1+(math.cos(angle) * speed) local nextY = y1+(math.sin(angle) * speed)   Timer.delayedCall(1000, function() apple:setPosition(nextX,nextY) end)

aditya

apple:setPosition is being called once in your code.

This should work.

local apple = Bitmap.new(Texture.new("apple.png")) apple:setAnchorPoint(0,0) stage:addChild(apple)   local pumpkin = Bitmap.new(Texture.new("pumpkin.png")) pumpkin:setAnchorPoint(0,0) stage:addChild(pumpkin) pumpkin:setPosition(100,100)     local speed = 5 local angle,x1,y1,x2,y2,nextX,nextY   function checkReached(x1,y1,x2,y2) local res = false if((x1>=x2-2 and x1<=x2+2) and (y1>=y2-2 and y1<=y2+2)) then res = true end return res end   function onEnterFrame(e) x1, y1 = apple:getPosition() x2, y2 = pumpkin:getPosition() print(x1 .. " " .. y1 .. " | " .. x2 .. " " ..y2)   if(checkReached(x1,y1,x2,y2)) then stage:removeEventListener(Event.ENTER_FRAME, onEnterFrame) else angle = math.atan2(y2-y1,x2-x1)   nextX = x1+(math.cos(angle) * speed) nextY = y1+(math.sin(angle) * speed)   apple:setPosition(nextX,nextY) end   end   stage:addEventListener(Event.ENTER_FRAME, onEnterFrame)

Tom2012

@aditya

Thank you! That works perfectly. Will be using that code in my game.

I'm embarrassed to say I was passing degrees rather than radians to math.cos / sin.

I thought was getting better at this stuff. ">

Thank you again for the replies and help folks.