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Detect wall between two points

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Detect wall between two points

5 replies

Detect wall between two points

Waldin
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10.06.17 08:38:42 am

hey guys I need help again

I have two points (lets call them A and B) and I need check if between the line of A and B is a wall (tile wall, or solid objects like wall, dispenser, etc) and know where is the wall (if there is one).
Like shoots, A is character and B the mouse, the shoot does't stop at mouse but wall. Thanks

Re: Detect wall between two points

Baloon
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10.06.17 08:52:34 am

Some sample from my scripts:

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local m=1
repeat
m=m+1
toX[id],toY[id]= player(id,"x")-math.sin(math.rad(player(id,"rot")+180))*m, player(id,"y")+math.cos(math.rad(player(id,"rot")+180))*m
until (tile(math.floor(toX[id]/32),math.floor(toY[id]/32),"wall")) or m>=itemtype(player(id,"weapontype"),"range")*3
toX[id], toY[id] = player(id,"x")-math.sin(math.rad(player(id,"rot")+180))*(m-1), player(id,"y")+math.cos(math.rad(player(id,"rot")+180))*(m-1)
xtoX[id], ytoY[id] = toX[id]+math.sin(math.rad(player(id,"rot")+180))*(m-1)/2, toY[id]-math.cos(math.rad(player(id,"rot")+180))*(m-1)/2
Dist= math.sqrt((player(id,"x")-toX[id])^2 + (player(id,"y")-toY[id])^2)
if zb.beam[id]~="" then
freeimage(zb.beam[id])
else
zb.beam[id]=0
end
zb.beam[id]= image("gfx/Zombie Brutality/beam.bmp",xtoX[id],ytoY[id],1)
imagepos(zb.beam[id],xtoX[id],ytoY[id],player(id,"rot")+math.random(-1,1))
imagescale(zb.beam[id],1,Dist)
alP=1
function LocalalP()
alP=alP-0.1
imagealpha(zb.beam[id],alP)
end
timer(5,"LocalalP","",10)

Re: Detect wall between two points

Talented Doge
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10.06.17 09:56:39 am

Consider the following image:

Image

The coordinate system is using Cartesian coordinate system, which you have already learnt early high school. You can take this approach, find the equation of the straight line, then see if there are walls that collide with the straight line.

Well, I am too lazy to figure out how to do this though.

Re: Detect wall between two points

DC
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10.06.17 10:13:38 am

One Algorithm you could use is Bresenham. With 1 tile in CS2D = 1 pixel in Bresenham. You can also use actual pixels though if you need high precision.

See https://en.wikipedia.org/wiki/Bresenham%27s_line_algorithm

Another approach is a raycast. You determine the direction between the two points with atan2 and move a point along that direction using sin & cos and keep checking if it hits something.

Re: Detect wall between two points

Waldin
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10.06.17 07:33:58 pm

Talented Doge: I was using something like that but it didnt work so good

maybe I did something wrong.
@

DC: Ill try raycasting and probably ask for help again later. TY

Re: Detect wall between two points

TrialAndError
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10.06.17 07:46:03 pm

I think this is what you need, it's commonly used in tibia.

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function distance(x1, y1, x2, y2)
    return math.floor(math.sqrt(math.pow(x1 - x2, 2) + math.pow(y1 - y2, 2)))
end

function freeline(x1, y1, x2, y2)
    for i=1, distance(x1, y1, x2, y2) do
        if tile(math.floor((x1 + i * math.cos(math.atan2(y2 - y1, x2 - x1))) / 32),math.floor((y1 + i * math.sin(math.atan2(y2 - y1, x2 - x1))) / 32), "walkable") == false then
            return false
        end
    end
    return true
end

There you can call freeline and put in your 2 coordinates and it will do the job (return true or false).