如何删除先前绘制的线？(How to delete a previously drawn line?

下面是代码：

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)

这些问题是：

1. 例如：我画一条线，然后我画下一条线，我想前行被删除。 我怎样才能做到这一点？
2. 我使用董事1.4，当我试图重播水平，线停下来正确绘制并出现错误是指向该行- if(lines[i]) then lineGroup:remove(i) end这样：如何我行添加到localGroup和重放水平时将其删除（我用director:changeScene("level1")或正确地变化的场景？

Answer 1:

嗯，我以为你想多行，因为你是把它们添加到一个行表。 如果你不需要多行，你可以存储1行。 就像是：

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)

将它们添加到当前场景，我相信导演类将是这样的：

function scene:createScene( event )
    lineGroup = self.view
end

你只需要设置lineGroup到scene.view而不是创建新组display.newGroup的（）

要正确删除行，你可以做到这一点在出口场景功能：

function scene:exitScene( event )
    if(line) then
        lineGroup:remove(1)
        line = nil
    end
end

我建议考虑看看导演类教程： http://www.youtube.com/watch?v=KudLE8h4kWw或此代码示例https://github.com/ansca/Storyboard-Sample

文章来源: How to delete a previously drawn line?