How do I get this variable out?

Peej

Peej

BBS

PICO-8 Tutorials

Embarrassing question but please be gentle. I'm very new to all this.
I have this code: (Lower down there). It's a bit mock up really for this question.

Lower down still in my code I'm working on a collision detection bit that needs, among other things, the value of x.
As you can see, it's all referencing 'self' and I have NO IDEA how to get the x value from this line:

spr(17,self.x,self.y,1,1,false)

Would someone please help a noob out.

Many thanks
Peej

function add_new_enemy()
    add(enemy,{
        x=80,
        y=96,
        w=8,
        h=8,
        dx=rnd(2)-1,
        dy=rnd(2)-1,
        life=20,
        draw=function(self)
            spr(17,self.x,self.y,1,1,false)
        end,

        update=function(self)
         self.x+=self.dx
         self.y+=self.dy
         self.life-=1
            if self.life<0 then
             del(enemy,self)
            end
        end
    })
end

P#94873 2021-07-15 00:15

merwok

So there are two ideas there: you have a table that is a sequence of things ('enemy', with things at index '1', '2', etc — would probably be better named 'enemies'), and in that table you have other tables (with values accessible by the indices 'x', 'y', 'w', etc)

Example to get the first enemy from the table:

-- get thing from a sequence table
enemy1 = enemy[1]

-- get thing from a mapping table
spr(17, enemy1["x"], enemy1["y"])

-- or using the dot shortcut (only works for string indices)
spr(17, enemy1.x, enemy1.y)

Now, you don’t want to do that for each enemy, so a loop can be used to do something for each item in the sequence:

for en in all(enemy) do
 -- 'en' is set to enemy[1] then enemy[2] etc until last
 spr(17, en.x, en.y)
end

The last thing is that a table can also contain functions. In the example you have, each enemy added to the enemy sequence table has 'x', 'y', etc but also 'draw' and 'update', meaning you can do this:

-- call a function that’s inside a table, passing the table for 'self' param
enemy1.draw(enemy1)

-- color is a shortcut to pass self automatically
enemy1:draw()

So putting all this together, this is how games typically update and draw multiple enemies or particles or items:

function _init()
 enemies = {}
end

function add_new_enemy()
 add(enemies, {etc etc})
end

function _update()
 -- call functions to check buttons, call add_new_enemy if some condition, etc
 update_player()
 update_world()

 for en in all(enemies) do
  en:update()
 end
end

function _draw()
 draw_background()
 draw_player()

 for en in all(enemies) do
  en:draw()
 end
end

Hope this helps!

P#94877 2021-07-15 01:20 ( Edited 2021-07-15 01:21)

Peej