How to delete a previously drawn line? - sdk

Question

Here is the code:
local physics = require "physics"
physics.start()
local lines = {}
local lineGroup = display.newGroup()
local prevX,prevY
local isDrawing = false
local i = 0
local function distanceBetween(x1, y1, x2, y2)
local dist_x = x2 - x1
local dist_y = y2 - y1
local distanceBetween = math.sqrt((dist_x*dist_x) + (dist_y*dist_y))
return distanceBetween
end
local function drawLine(e)
if(e.phase == "began") then
prevX = e.x
prevY = e.y
isDrawing = true
i = i + 1
print"began"
elseif(e.phase == "moved") then
local distance = distanceBetween(prevX, prevY, e.x, e.y)
if(isDrawing and distance < 100) then
if(lines[i]) then lineGroup:remove(i) end
lines[i] = display.newLine(prevX, prevY, e.x, e.y)
lines[i]:setColor(255, 255, 0)
lines[i].width = 5
local dist_x = e.x - prevX
local dist_y = e.y - prevY
physics.addBody(lines[i], "static", { density = 1, friction = 0.5, bounce = 1.6, shape = {0, 0, dist_x, dist_y, 0, 0} } )
lineGroup:insert(lines[i])
end
elseif(e.phase == "ended") then
isDrawing = false
end
end
Runtime:addEventListener("touch",drawLine)
The questions are:
For example: I draw a line, then I draw the next line and I want the previous line to be deleted. How can I do this?
I am using director 1.4 and when I am trying to replay level, the lines stop to draw correctly and the error appears that is pointing to this line - if(lines[i]) then lineGroup:remove(i) end so: How can I add lines to the localGroup and delete them when replaying level (I am using director:changeScene("level1") or changing scene correctly?

Answer 1

Hmm, I assumed you wanted multiple lines because you was adding them to a lines table. If you don't need multiple lines, you can just store the 1 line. Something like:
local physics = require "physics"
physics.start()
local line
local lineGroup = display.newGroup()
local prevX,prevY
local isDrawing = false
local i = 0
local function distanceBetween(x1, y1, x2, y2)
local dist_x = x2 - x1
local dist_y = y2 - y1
local distanceBetween = math.sqrt((dist_x*dist_x) + (dist_y*dist_y))
return distanceBetween
end
local function drawLine(e)
if(e.phase == "began") then
if(line) then
lineGroup:remove(1)
line = nil
end
prevX = e.x
prevY = e.y
isDrawing = true
elseif(e.phase == "moved") then
local distance = distanceBetween(prevX, prevY, e.x, e.y)
if(isDrawing and distance < 100) then
if(line) then lineGroup:remove(1) end
line = display.newLine(prevX, prevY, e.x, e.y)
line:setColor(255, 255, 0)
line.width = 5
local dist_x = e.x - prevX
local dist_y = e.y - prevY
physics.addBody(line, "static", { density = 1, friction = 0.5, bounce = 1.6, shape = {0, 0, dist_x, dist_y, 0, 0} } )
lineGroup:insert(line)
end
elseif(e.phase == "ended") then
isDrawing = false
end
end
Runtime:addEventListener("touch",drawLine)
To add them to the current scene, I believe the director class would be something like this:
function scene:createScene( event )
lineGroup = self.view
end
You just need to set the lineGroup to the scene.view instead of creating a new group with display.newGroup()
To properly remove the line, you can do it in the exit scene function:
function scene:exitScene( event )
if(line) then
lineGroup:remove(1)
line = nil
end
end
I'd recommend taking a look at the director class tutorials: http://www.youtube.com/watch?v=KudLE8h4kWw or this code sample https://github.com/ansca/Storyboard-Sample