Pico-8 Winter Forest Renderer

p={}
depth={}
pos={}

groundy=-6

function getindex(x,y)
    x=flr(x)
    y=flr(y)

    if (x%128!=x or y%128!=y) return nil

    return x*128+y
end

function rnddir(ground)
    local a=rnd()
    local y=rnd(2)-1
    local r=sqrt(1-y*y)
    local x=cos(a)*r
    local z=sin(a)*r
    if ground then
        y=abs(y)
    else
        z=-abs(z)
    end
    return x,y,z
end

function worldtoscr(x,y,z)
    local persp=60/z

    local u=64+x*persp
    local v=64-y*persp
    return u,v,persp
end

function scrtoworld(u,v)
    local y=groundy
    local persp=(64-v)/y

    local x=(u-64)/persp
    local z=60/persp
    return x,y,z,persp
end

dirsx={1,-1,0,0}
dirsy={0,0,1,-1}

function outline(u,v)
    local index=getindex(u,v)
    local dist=depth[index]

    for i=1,#dirsx do
        local u2=u+dirsx[i]
        local v2=v+dirsy[i]
        local index2=getindex(u2,v2)
        if index2 then
            local dist2=depth[index2]
            if dist2 then
                if dist2>dist*1.1+sqrt(dist)*.5 then
                    return true
                end
            else
                return true
            end
        end
    end

    return false
end

function ssao(point,dist)
    local x=point[1]
    local y=point[2]
    local z=point[3]
    local ground = (y==groundy)
    local hits=0
    local totalweight=0
    local raycount=60
    local raysamples=4
    local _,__,persp=worldtoscr(x,y,z)
    local raylen=4/persp
    for i=1,raycount do
        local dx,dy,dz=rnddir(ground)
        local rayhits=0
        local weight=1
        for j=1,raysamples do
            local d=j/raysamples*raylen
            local u,v=worldtoscr(x+dx*d,y+dy*d,z+dz*d)
            local index=getindex(u,v)
            if index then
                local otherdepth=depth[index]
                if otherdepth and otherdepth<dist then
                    rayhits+=1/raysamples
                end
            else
                if rayhits==0 then
                    break
                end
            end
        end
        hits+=rayhits*rayhits*weight
        totalweight+=weight
    end

    return 1-(hits/totalweight)^2
end

function drawpoint(x,y,z,u,v)
    if not u then
        u,v=worldtoscr(x,y,z)
    end

    index=getindex(u,v)
    if index then
     dist=z
     if not depth[index] or dist<depth[index] then
            col=sqrt(dist/50)*15
            pset(u,v,col)
            depth[index]=dist
            if pos[index] then
                pos[index][1]=x
                pos[index][2]=y
                pos[index][3]=z
            else
                pos[index]={x,y,z}
            end
        end
    end
end

function drawleaf(lx,ly,lz,count,jit)
    for j=1,count do
        x=lx+rnd(jit)-jit/2
        y=ly+rnd(jit)-jit/2
        z=lz+rnd(jit)-jit/2

        drawpoint(x,y,z)
    end
end

function maketree(tx,tz)
    local height=rnd(6)+6
    for i=0,100 do
        t=i/100
        l=3*(1-t^2)
        a=i*.618+.1
        dx=cos(a)
        dz=sin(a)
        for j=0,l,.1 do
            t2=j/l
            x=dx*j+tx
            y=groundy+t*height-j/2
            z=dz*j+tz
            drawleaf(x,y,z+8,8,.3)
        end
    end
end

function makeplant(x,z)
    local h=rnd(2)
    for i=0,h,.1 do
        for j=1,1 do
            drawpoint(x+rnd(.2)-.1,
                      groundy+i,
                      z+rnd(.2)-.1)
        end
    end
end

function makemountain(x,z,h)
    local u,v,persp=worldtoscr(x,groundy,z)
    local wheight=h/persp
    local y=groundy+wheight
    local u2,v2=worldtoscr(x,y,z)
    local sheight=v-v2
    for i=0,sheight,.2 do
        local t=i/sheight
        local radius=t*wheight
        for a=0,.5,.1/radius do
            local dx=cos(a)*radius
            local dz=sin(a)*radius
            local wave=sin(a*12+t*4)*2/persp
            drawpoint(x+dx,y-wheight*t+wave-rnd(6)/persp,z+dz)
        end
    end

end

function makecloud(x,y,z,screenw)
    local u,v,persp=worldtoscr(x,y,z)
    local w=screenw/persp
    for i=1,80 do
        drawleaf(x+rnd(w)-w/2,
                 y+rnd(w/8)-w/16,
                 z+rnd(w/8)-w/16,
                 80,
                 w/20)
    end
end

cls(13)

for u=0,127 do
    for v=65,127 do
        index=getindex(u,v)
        x,y,z=scrtoworld(u,v)
        drawpoint(x,y,z,u,v)
    end
end


srand(3)
nextseed=rnd(-1)
for i=1,8 do
    makemountain(rnd(400)-200,
                 200+i*30,
                 15+rnd(30))
    srand(nextseed)
    nextseed=rnd(-1)
end

srand(0)
nextseed=rnd(-1)
for i=1,20 do
    makecloud(rnd(1000)-500,
              350+rnd(100),
              500+rnd(200),
              rnd(60)+30)
    srand(nextseed)
    nextseed=rnd(-1)
end

srand(0)
nextseed=rnd(-1)
for j=0,4 do
    for i=-1-j,1+j do
        maketree((i+rnd()-.5)*7,
                 (j+rnd()-.5)*6)
        srand(nextseed)
        nextseed=rnd(-1)
    end
end

srand(0)
nextseed=rnd(-1)
for i=1,100 do
    local px=rnd(20)-10
    local pz=rnd(12)+3
    for j=1,5+rnd(10) do
        makeplant(px+rnd(2)-1,
                  pz+rnd(1)-.5)
    end
    srand(nextseed)
    nextseed=rnd(-1)
end

for u=0,127 do
    for v=0,127 do
        index=getindex(u,v)
        dist=depth[index]
        if dist then
            light=ssao(pos[index],dist)
            //light+=(.5-light)*mid(dist/1200,0,1)
            local col=5+light*2.5
            if outline(u,v) then
                //col=1+flr(light*1.2)*4
                col=5
            end
            pset(u,v,col)
        end
    end
end

function _update()
end