如何防止 renderBlocks() 函数进入无限循环？

Question

-- This is Minecraft, but 2D, and in Lua.

-- **************************************
-- ID 0: Air
-- ID 1: Stone
-- ID 2 Logs
-- ID 3: Leaves
-- ID 4: Planks
-- ID 5: Crafting Table
-- ID 6: Furnance
-- ID 7: Player position detector block
-- **************************************

blockTable = { -- Stores all the blocks
    {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
    {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
    {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
    {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
    {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
    {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
    {0,0,0,0,0,0,0,0,0,7,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
    {6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6}
}
tableRow = 1 -- Y value for block render pointer
tableColumn = 1 -- X value for block render pointer
runOnce = true -- Run a loop once
tickNum = 0 -- Number of ticks since startup
function renderBlock(X, Y, K) -- Render a block
    if K == 1 then -- if blockID == 1, draw a grey square
        screen.setColor(100,100,100)
        print(X, Y)
        screen.drawRectF(X, Y, 8, 8)
    end
    if K == 6 then -- If the blockID == draw a grey square
        screen.setColor(100,100,100)
        screen.drawRectF(X, Y, 8, 8)
    end
end

function renderBlocks() -- Render all the blocks (Scans though the blockTable in a raster pattern)
        while runOnce == true -- Run this code once
    do
    while #blockTable >= tableRow
    do
        while #blockTable[tableRow] >= tableColumn
        do
            print("TC " .. tableColumn)
            tableColumn = tableColumn + 1
            
            blockID = blockTable[tableRow][tableColumn]
            renderBlock(tableRow, tableColumn, blockID)
            if tableColumn > #blockTable[tableRow] then tableColumn = 1 end
        end
        runOnce = false
    end
        print("TR " .. tableRow)
        tableRow = tableRow + 1
    end
end

function onTick()
    print("Tick! Tick count: " .. tickNum) -- Print the current tick, as well as say that there has been a tick
    tickNum = tickNum + 1
end

function onDraw()
    while runOnce == true -- Run this code once
    do
    renderBlocks()
    runOnce = false
    end
end

这是我在框架 IDE 中的代码：Link

我不知道为什么会这样，我在这里不知所措。

Answer 1

在对表执行循环时，使用 for 循环比使用 while 或重复循环要好得多，后者更难理解和修复错误。

如果您想获取索引（表中的数字）和关联的值，请使用for index,value in ipairs(yourtable) do，如果您想获取键（通常用作值的键的字符串：yourTable["key"] = 0），请使用for key,value in pairs(yourtable) do ) 以及与之关联的值。

for row,innerTable in ipairs(blockTable) do
        
    for col,value in ipairs(innerTable) do
            
        print("TC " .. col)
            
        blockID = value
        renderBlock(row, col, blockID)
            
    end
        
end

最后一个应该在你的 renderBlocks 函数中完成。但是：

while runOnce == true do

    -- Doing something
    runOnce = false

end

不是很好的东西。如果只调用一次，不要循环！

此外，更好地识别代码有助于更快地了解正在发生的事情。并在处理不同问题的代码块之间添加一些空格。

编辑：所以你的函数可能看起来像这样：

function renderBlocks()
    if runOnce then
        runOnce = false
        for row,innerTable in ipairs(blockTable) do
            for col,value in ipairs(innerTable) do
                blockID = value
                renderBlock(row, col, blockID)
            end
        end
    end
end

Answer 2

您的 renderBlocks() 函数中有几个问题

function renderBlocks()
  while runOnce == true do
    while #blockTable >= tableRow do
      while #blockTable[tableRow] >= tableColumn do
        print("TC " .. tableColumn)
        tableColumn = tableColumn + 1

        blockID = blockTable[tableRow][tableColumn]
        renderBlock(tableRow, tableColumn, blockID)
        if tableColumn > #blockTable[tableRow] then 
          tableColumn = 1 
        end
      end
      runOnce = false
    end
    print("TR " .. tableRow)
    tableRow = tableRow + 1
  end
end

首先我们可以看看最里面的循环。在这里，我们遇到了用于评估循环的悔改以及如何递增的问题。

while #blockTable[tableRow] >= tableColumn do
  print("TC " .. tableColumn)
  tableColumn = tableColumn + 1 -- incremented here

  blockID = blockTable[tableRow][tableColumn]
  renderBlock(tableRow, tableColumn, blockID)
  if tableColumn > #blockTable[tableRow] then 
    tableColumn = 1 -- reset here
  end
end

在循环体中你执行tableColumn = tableColumn + 1 和稍后在同一个主体中执行if tableColumn > #blockTable[tableRow] then tableColumn = 1 end 所以这是一个问题，当tableColumn 增加到一个会结束循环的值时，我们将它重置为1 防止永无止境的循环。

现在让我们看看下一个循环。这里我们从不增加tableRow，它只是在循环结束后增加，所以循环不可能结束。

while #blockTable >= tableRow do
    while #blockTable[tableRow] >= tableColumn do
        ...
    end
    runOnce = false
end

我相信你是故意的

print("TR " .. tableRow)
tableRow = tableRow + 1

发生在这个循环内而不是在它之外。

Answer 3

您在这里缺少一些块定义。不要认为这是将其发送到无限循环的原因，否则您可能看不到结果。

function renderBlock(X, Y, blockID)  --  Render a block
  if blockID == 0 then  --  Air
    --  screen.setColor(10, 20, 220, 0) -- is there an alpha channel?
    screen.setColor(10, 20, 220)

  elseif blockID == 1 then  --  Stone
    screen.setColor(100, 100, 100)

  elseif blockID == 2 then  --  Logs
    screen.setColor(200, 50, 50)

  elseif blockID == 3 then  --  Leaves
    screen.setColor(20, 220, 40)

  elseif blockID == 4 then  --  Planks
    screen.setColor(180, 30, 10)

  elseif blockID == 5 then  --  Craft Table
    screen.setColor(180, 30, 10)

  elseif blockID == 6 then  --  Furnace
    screen.setColor(100, 100, 100)

  elseif blockID == 7 then  --  Player detect
    screen.setColor(220, 30, 30)
  end

  print(X, Y)
  screen.drawRectF(X, Y, 8, 8)
end

for 循环很容易使用。设置初始条件，然后设置最终的完成条件，并让它运行课程。

function renderBlocks() -- Render all blocks (Scans though blockTable in a raster pattern)
  for row = 1,  #blockTable do
    for col = 1, #blockTable[row] do
      print("TC " ..col)
      local blockID = blockTable[row][col]
      renderBlock(row, col, blockID)
    end
    print("TR " ..row)
  end
end

您可能不需要runOnce。如果你发现你在做其他事情，请继续，但嵌套 for 循环不应该需要它。

function onDraw()
  renderBlocks()
end