How can I get rid of this extra math

Tom2012 · November 2012

In the code below I need to fire something towards another object using Atan2, cos and sin

It works, but I'm converting to degrees and then back to radians. (I'm guessing this has some overhead).

Snippet:

	local angle = math.atan2(yDiff,xDiff)
	angle = math.deg(angle) + 180
 
	local nextX = ball:getX() + (math.cos(math.rad(angle)) * move)
	local nextY = ball:getY() + (math.sin(math.rad(angle)) * move)

Is there a better way to 'reverse' the angle?

Thank you!

-- Add hero
 
local hero = Bitmap.new(Texture.new("gfx/happy-block.png"))
hero:setAnchorPoint(.5,.5)
stage:addChild(hero)
hero:setPosition(100,100)
 
-- Add ball
 
local ball = Bitmap.new(Texture.new("gfx/ball.png"))
ball:setAnchorPoint(.5,.5)
stage:addChild(ball)
ball:setPosition(400,200)
 
 
-- pixels moved each frame
local move = 1;
 
local moving = false -- keep track of if ball already moving
 
-- This function moves the ball each frame
 
function moveBall()
 
	local xDiff = ball:getX() - hero:getX()
	local yDiff = ball:getY() - hero:getY()
 
	local angle = math.atan2(yDiff,xDiff)
	angle = math.deg(angle) + 180
 
	local nextX = ball:getX() + (math.cos(math.rad(angle)) * move)
	local nextY = ball:getY() + (math.sin(math.rad(angle)) * move)
 
	--print(nextX, nextY)
 
	ball:setPosition(nextX,nextY)
 
end
 
function touchedEnd(event)
 
	if(not moving) then
 
		moving = true
		ball:setPosition(event.touch.x, event.touch.y) -- move ball to touch x,y
		stage:addEventListener(Event.ENTER_FRAME, moveBall) -- add event listener to move ball each frame
 
 
	end
 
end
 
stage:addEventListener(Event.TOUCHES_END, touchedEnd)

techdojo · November 2012

As both sin, cos and atan2 all work in radians, why not just work in radians all the time and in the line

angle = math.deg(angle) + 180

change it to

 angle = angle + (180 * 0.0174532925) -- 1 degrees = 0.0174532925 radians

Tom2012 · November 2012

Ah, thanks. That works great.

zvardin · November 2012

Also, I believe I read you can get some improvements by storing math functions into local functions when you're going to be using them a lot.

So, you can store any math functions you're going to use like:

local sin = math.sin

techdojo · November 2012

@Tom2012 - absolutely, should have mentioned that

OZApps · November 2012

...and set up a variable to contain the constant deg2rad so that you know what that magic number is/was when you revisit the code.

Howdy, Stranger!

Categories

In this Discussion

Top Posters

How can I get rid of this extra math

Comments

Howdy, Stranger!

Quick Links

Categories

In this Discussion

Top Posters

How can I get rid of this extra math

Comments