Playdate 6

When all else fails and there’s nothing you can do: keep busy, I guess?

So, building on yesterday’s demo, I wanted to make my little ghost eat the dots as it passes over them. First step is working out when the ghost – which is moving in increments of 4px – has entered a new 16px unit of the map.

To test that, a helper function:

function isMultipleOf(testThis,divideBy)
    if (testThis/divideBy == math.floor(testThis/divideBy)) then 
        return true
    else
        return false
    end    
end

And then when moving the ghost, use that to check:

if isMultipleOf(playerSprite.x - topLeft,16) then
   if isMultipleOf(playerSprite.y,16) then
      -- exactly on a square
      checkForEat(((playerSprite.x-topLeft)/16)+1,(playerSprite.y/16)+1)
   end    
end  

(Side note – I couldn’t get the code to compile when checking for both the isMultipleOf checks at once (if x AND y then). Could have just been a typo, need to check.)

In the call to checkForEat, we’re converting the pixel locations of the sprite (playerSprite.x, playerSprite.y) into a 1-indexed grid reference showing the sprite’s location in the 15 by 15 level – eg, x,y from 1,1 to 15,15.

We pass those to the function checkForEat, where we cast them to integers, and look up what tile is currently shown on that bit of the map:

function checkForEat(gridX,gridY)
    -- check: is there a dot there? If so, we eat it

    gridX = math.floor(gridX) -- cast to int in an ugly way
    gridY = math.floor(gridY) 

    if map:getTileAtPosition(gridX,gridY) == 3 then   
        -- on a dot! chompy time
        updateScore(100)
        -- remove it
        map:setTileAtPosition(gridX, gridY, 2)
    end    
end 

If it’s 3 (my “dot” graphic), then we increase the score – via a function that will, later, draw the score somewhere too – and then update the tilemap to show a blank tile (tile 2) using setTileAtPosition.

So now as the ghost bobbles about, it eats the dots, and starts building a score:

Full code here.