CODEWITHSUNDEEP
luacoronasdk
Dips
Dips

Reputation: 145

Prevent spawns being placed In the same Xpos on different Y position - Corona SDK

I seem to be having an issue which I cannot solve properly and need some help. Looking at the image below, I am spawning shapes from a table called enemies and am trying to check if their x positions are occupied by a spawn, if so, then slightly move it left or right so it pops out enough to hit them as they move downwards. The image shows a problem where shapes are stacked behind each other.

Image showing the main problem, and an example of perfect spacing

Spawn function (called from the game loop)

local xPos = math.random(22,279)
local r = math.random(1, #spawnData)

local sd = spawnData[r] -- get the spawn data for this enemy 

local s = display.newSprite(sd.imgSheet, sd.seqData)
s.name = sd.name
physics.addBody(s, {isSensor = true})
s:setSequence(sd.seq)
s:setFrame(sd.frame)
s.y = display.contentHeight - 550 -- Create the enemies using spawnData 

local ok = false -- A flag to say whether we found a valid X position  
local gap = 2     -- Set the minimum gap in pixels between enemies 
local err = 0    -- An error flag to avoid the game slowing down if too many enemies 

while ok == false do -- Tell it to loop until a valid X position is found 
    xPos = math.random(20,300) -- give a new X position 
    ok = true -- Until it has checked against other enemies, assume it is ok for now 

    for i = 1, #enemies, 1 do -- Loop through the previously spawned enemies 
       local e = enemies[i] -- Link to this enemy

       local dist = mAbs(e.x - xPos) -- Work out the distance between this enemy and the random position chosen 
       if dist < (e.width + gap) then ok = false end -- If the enemies are too close, try agian 
    end 

    err = err + 1 -- Increase the count of attempts to find a valid position 
    if err > 50 then ok = true end -- After 50 tries, assume there is no empty space and just spawn wherever
end

s.x = xPos
enemies[#enemies+1] = s

enemyGroup:insert(s)

Upvotes: 1

Views: 80

Answers (1)

Brett Comardelle
Brett Comardelle

Reputation: 322

You have two snippets of code that aid this error.

In this first snippet, you are looking at every sprite that has existed and trying to find an appropriate x position. With many sprites, the error becomes more prone. Try to only look at the previous Sprite's x position.

for i = 1, #enemies, 1 do -- Loop through the previously spawned enemies 
       local e = enemies[i] -- Link to this enemy

       local dist = mAbs(e.x - xPos) -- Work out the distance between this enemy and the random position chosen 
       if dist < (e.width + gap) then ok = false end -- If the enemies are too close, try agian 
    end

In this next snippet, after 50 errors are made, it places the sprite anywhere. You are allowing this spawn to occur. Try a larger value. However, that is going to only postpone the issue.

err = err + 1 -- Increase the count of attempts to find a valid position 
    if err > 50 then ok = true end -- After 50 tries, assume there is no empty space and just spawn wherever

Edit:

Here is what I would do. There may be errors because I did not test it. Hopefully it does give you the idea of what should be done, though.

    local xPos = math.random(22,279)
    local r = math.random(1, #spawnData)

    local sd = spawnData[r] -- get the spawn data for this enemy 

    local s = display.newSprite(sd.imgSheet, sd.seqData)
    s.name = sd.name
    physics.addBody(s, {isSensor = true})
    s:setSequence(sd.seq)
    s:setFrame(sd.frame)
    s.y = display.contentHeight - 550 -- Create the enemies using spawnData 

    local ok = false -- A flag to say whether we found a valid X position  
    local gap = 2     -- Set the minimum gap in pixels between enemies 
    local err = 0    -- An error flag to avoid the game slowing down if too many enemies 

-- EDITED CODE BELOW
--------------------
    while ok == false do -- Tell it to loop until a valid X position is found 
        xPos = math.random(20,300) -- give a new X position 

        local e = enemies[#enemies] -- Get the last enemy in the table (should be the previously made)

        if e == nil then
           break  -- Break out of the while loop
        end

        local dist = mAbs(e.x - xPos) -- Work out the distance between this enemy and the random position chosen
        if dist >= (e.width + gap) then
            ok = true
        else
            err = err + 1 -- Increase the count of attempts to find a valid position
            if err > 50 then
                ok = true
            end
        end
    end

    s.x = xPos
    enemies[#enemies+1] = s

    enemyGroup:insert(s)

Upvotes: 0

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