Connect 4 Drop Code for PICO-8

connect4.p8

-- I'm using sprite 1 and 2 for drawing, so draw something there

units = {}
cursor = {
    x = 1,
    y = 1
}
bottom_of_board = 9
is_green = true

function create_new_unit(name, health, attack, is_green)
    local unit = {
        name = name,
        health = health,
        attack = attack,
        is_green = is_green,
        let_go = false, -- we haven't let it go from cursor
        is_placed = false -- we haven't placed it yet on the board
    }
    -- add the new unit to the tablethat holds all of them
    -- we know the new unit is one at the very end, but
    -- with our logic we can use let_go and is_placed so
    -- apply movement to a specific few ones
    add(units, unit)
end

function _init()
    -- start with a unit in hand
    create_new_unit("goblin", 1, 2, is_green)
end

function _update()
    if btnp(0) then cursor.x -= 1 end
    if btnp(1) then cursor.x += 1 end

    for unit in all(units) do
        -- if the unit was let go then
        -- we are gonna inlcude this is_placed, so we can
        -- skip all this code for units that alrady reached a valid place
        if unit.let_go and (not unit.is_placed) then
            -- is there something below the unit
            local next_y = unit.y + 1
            -- is it the bottom of the board?
            if next_y == bottom_of_board then
                -- we cannot go lower, so set it back to the
                -- original y level
                next_y = unit.y
                -- now "place" the unit, so we don't have to
                -- run all this code again
                unit.is_placed = true
                -- flip color, does nothing so far
                is_green = not is_green
                create_new_unit("goblin", 1, 2, is_green)
            end
                -- we can move lower, so check if there is something
                -- under us, if there are other units
            if not (unit.is_placed) then
                for other_unit in all(units) do
                    -- this would include a check against itself,
                    -- so do not let that
                    if other_unit ~= unit then
                        -- now check if we are on the same x pos,
                        -- aka column
                        if  other_unit.x == unit.x then
                            -- we now need to check if we are over them
                            -- because if so, we don't move one mor slot down
                            -- as that would be an overlap
                            if other_unit.y == next_y then
                                -- now "place" the unit, so we don't have to
                                -- run all this code again
                                unit.is_placed = true
                                -- set the next pos to the current, so we will not move 
                                -- more down
                                next_y = unit.y
                                -- flip the color, does nothing so far
                                is_green = not is_green
                                create_new_unit("goblin", 1, 2, is_green)
                            end 
                        end 
                    end
                end
            end
            unit.y = next_y
        elseif (not unit.is_placed) then
            -- if we haven't let go yet, it follows the cursor
            -- we do need to check of is_placed, as we let go of those
            -- units already, but we did place them so we can filter those
            -- out and only the the ONE unit we haven't placed or let go yet
            unit.x = cursor.x
            unit.y = cursor.y 
        end
    end
    -- we are always playing with the last unit, which is at the tables length
    -- if we have 5 units, the last one is the 5th, which is the lenght of the table
    -- #table returns the length of it
    if btnp(5) then units[#units].let_go = true end

end

function _draw()
    cls()
    map()
    -- draw cursor, we want map tiles so it aligns to the grid nicely
    spr(15, cursor.x*8, cursor.y*8)

    -- draw units
    for unit in all(units) do
        spr(unit.is_green and 1 or 2, unit.x*8, unit.y*8)
    end
end