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stanleycan8668

Error: Attempt to index global 'W' (a nil value)

Hello! I am having trouble getting collision working with a different system that spawns sprites in from the map screen.

This is the collision tutorial I used: https://youtu.be/Recf5_RJbZI?si=Df6FbJ2FYfCN39Qx
This is the sprite spawning tutorial I used: https://youtu.be/8jb8SHNS66c?si=233nn8z_S1R4R64n

I have watched TONS of tutorials on this and still can't wrap my head around it. A lot of tutorials create very basic collision that has issues, like only being able to work with certain speed values (1,2,4,8,16,etc.) or that don't let your character slide alongside a wall when holding a diagonal.

Can anyone help? I definitely want to use this spawning system in the future to spawn in different types of walls and enemies. I have a feeling that I am misunderstanding how to use the table variables properly, so any explanation would be appreciated!

 
-- game loop --

function _init()
    cls()
    walls={}
    make_player()
    make_walls()
    -- top-left and lower-right
    -- bounds of player area
    a1,b1=8,8
    a2,b2=112,112
end

function _update60()
    -- keep inside the play area
    move_player()
    p.x=mid(a1,p.x,a2)
    p.y=mid(b1,p.y,b2)
end

function _draw()
    cls()
    draw_map()
    draw_player()

    for w in all(walls) do
        spr(w.wsp,w.wx,w.wy)
    end 
end
 
-- map --

function draw_map()
    map(0,0,0,0,16,16)
end
 
-- player --

function make_player()
    p={
    x=40,
    y=40,
    w=8,
    h=8,
    speed=2,
    sprite=1,
    }
end

function move_player()
    --move player with buttons
    --interacts with wall collision
    if (btn(⬅️)) then
        for newx=p.x,p.x-p.speed,-1 
            do
                if not box_hit(newx,p.y,
                    p.w,p.h,
                    w.wx,w.wy,
                    w.ww,w.wh) 
                then
                    p.x=newx
            end
        end
    end

        if (btn(➡️)) then
        for newx=p.x,p.x+p.speed 
            do
                if not box_hit(newx,p.y,
                        p.w,p.h,
                        w.wx,w.wy,
                        w.ww,w.wh) 
                then
                    p.x=newx
            end
        end
    end

        if (btn(⬆️)) then
        for newy=p.y,p.y-p.speed,-1 
            do
                if not box_hit(p.x,newy,
                        p.w,p.h,
                        w.wx,w.wy,
                        w.ww,w.wh) 
                then
                    p.y=newy
            end
        end
    end

        if (btn(⬇️)) then
        for newy=p.y,p.y+p.speed 
            do
                if not box_hit(p.x,newy,
                        p.w,p.h,
                        w.wx,w.wy,
                        w.ww,w.wh) 
                then
                    p.y=newy
            end
        end
    end
end

--draw player
function draw_player()
    spr(p.sprite,p.x,p.y)
end
 
-- walls --

function make_walls()
    for x=0,15 do
        for y=0,15 do
            if mget(x,y)==65 then
                add(walls,{
                    wx=x*8,
                    wy=y*8,
                    ww=8,
                    wh=8,
                    wsp=66
                })
                mset(x,y,64)
            end
        end
    end
end

--wall collision calculations

function box_hit(x1,y1,
        w1,h1,
        x2,y2,
        w2,h2)

        local hit=false
        local xd=abs((x1+(w1/2))-(x2+w2/2))
        local xs=w1/2+w2/2
        local yd=abs((y1+(h1/2))-(y2+h2/2))
        local ys=h1/2+h2/2  

    if xd < xs and yd < ys then
        hit=true
    end

    return hit

end
P#135552 2023-10-06 23:45


2bitchuck
2bitchuck
1

Your error is probably coming from your calls to box_hit() in the move_player(). You're passing w.wx, w.wy, etc to that call, but you don't have a variable named w anywhere, so w is nil, which means w.wx etc. will cause an error.

You probably need to get the wall you want to check collision with from the walls table, assign that to w, then make your call to box_hit().

P#135554 2023-10-07 01:17

stanleycan8668
stanleycan8668

Oh yes, you're absolutely right! However when that is fixed, it still returns a nil value for the other variables in the wall table. For example, my WX, WY, WW, and WH are all nil.

How should I use this function to let the game know the coordinates and width/height of all of my wall sprites on the screen?

P#135556 2023-10-07 01:46

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