Flickering lights

gistfile1.txt

--flickering lights
function setup()
    --set up dark area covered by shader
    SS_Dark.setup(WIDTH,600,true)
    --add an unblinking light that can be moved
    L1Pos=vec2(150,175)  --initial pos of light1
    L1=SS_Dark.AddLight(L1Pos.x,L1Pos.y,150,0)
    --add a flickering light (30% flicker)
    L2=SS_Dark.AddLight(600,125,150,0.3)
    --another light with a bigger flicker
    L3=SS_Dark.AddLight(400,325,100,0.6)
    print("Drag the first light round the screen with your finger")
end

function draw() 
    --give ourselves a background behind the dark
    sprite("Cargo Bot:Starry Background",WIDTH/2,HEIGHT/2,WIDTH,HEIGHT)
    SS_Dark.draw() --this draws the dark and the lights
end

--drag L1 light with finger
function touched(t)
    if t.state==MOVING then
        L1Pos=L1Pos + vec2(t.x-t.prevX,t.y-t.prevY)
        SS_Dark.SetLight(L1,nil,L1Pos.x,L1Pos.y)  --set new position
    end
end

--Darkness and lighting code
--up to 3 lights can be controlled at once
SS_Dark={}

--w, h is width and height of rectangle containing lights
--everything except the lights will be black
--the darkness will fade towards the top if fade=true
function SS_Dark.setup(w,h,fade)
    SS_Dark.width=w     
    SS_Dark.height=h     
    SS_Dark.Lights={}
    SS_Dark.mesh=mesh()
    SS_Dark.mesh:addRect(w/2,h/2,w,h)
    SS_Dark.mesh.shader=shader(SS_Dark.shader.v,SS_Dark.shader.f)
    if fade then SS_Dark.mesh.shader.topY=h else SS_Dark.mesh.shader.topY=0 end
    SS_Dark.mesh.shader.lightRadius1=0
    SS_Dark.mesh.shader.lightRadius2=0
    SS_Dark.mesh.shader.lightRadius3=0
    SS_Dark.mesh.shader.lightPos1=vec4(0,0,0,0)
    SS_Dark.mesh.shader.lightPos2=vec4(0,0,0,0)
    SS_Dark.mesh.shader.lightPos3=vec4(0,0,0,0)
end

--shader lights can't be held in array, must be separate variables
--this next function allocates a new light to the next available shader variable
--making it easy to add and remove lights dynamically without having to worry about what the
--shader calls them
--x,y is position within the dark rectangle
--r is radius of the light
--f is the extent of the flicker (0-1, omit if no flicker)
--returns the id of the light
function SS_Dark.AddLight(x,y,r,f)
    local id
    for i=1,3 do
        if SS_Dark.Lights[i]==nil then id=i break end
    end
    if not id then return end
    if id==1 then
        SS_Dark.mesh.shader.lightRadius1=r or 100
        SS_Dark.mesh.shader.lightFlicker1=f or 1
        SS_Dark.mesh.shader.lightPos1=vec4(x,y,0,1)        
    elseif id==2 then
        SS_Dark.mesh.shader.lightRadius2=r or 100
        SS_Dark.mesh.shader.lightFlicker2=f or 1
        SS_Dark.mesh.shader.lightPos2=vec4(x,y,0,1)      
    elseif id==3 then
        SS_Dark.mesh.shader.lightRadius3=r or 100
        SS_Dark.mesh.shader.lightFlicker3=f or 1
        SS_Dark.mesh.shader.lightPos3=vec4(x,y,0,1)       
    end
    --the n variable is included to make the flicker different for each light
    SS_Dark.Lights[id]={x=x,y=y,radius=r or 50,flicker=(f or 0),n=math.random()}
    
    return id
end

--use this to change the current flicker or x,y, or radius
function SS_Dark.SetLight(id,f,x,y,r)
    if id==1 then
        if f then SS_Dark.mesh.shader.lightFlicker1=f end
        if x and y then SS_Dark.mesh.shader.lightPos1=vec4(x,y,0,1) end
        if r then SS_Dark.mesh.shader.lightRadius1=r end
    elseif id==2 then
        if f then SS_Dark.mesh.shader.lightFlicker2=f end
        if x and y then SS_Dark.mesh.shader.lightPos2=vec4(x,y,0,1) end
        if r then SS_Dark.mesh.shader.lightRadius2=r end
    elseif id==3 then
        if f then SS_Dark.mesh.shader.lightFlicker3=f end
        if x and y then SS_Dark.mesh.shader.lightPos3=vec4(x,y,0,1) end
        if r then SS_Dark.mesh.shader.lightRadius3=r end
    end
end

function SS_Dark.RemoveLight(id)
    SS_Dark.Lights[id]=nil
    if id==1 then     SS_Dark.mesh.shader.lightRadius1=vec2(0,0)
    elseif id==2 then SS_Dark.mesh.shader.lightRadius2=vec2(0,0)
    elseif id==3 then SS_Dark.mesh.shader.lightRadius3=vec2(0,0)
    end
end

function SS_Dark.draw() 
    --set flicker for current lights
    --use noise function to cause flicker
    for id=1,3 do
        if SS_Dark.Lights[id] ~=nil then 
            SS_Dark.SetLight(id,1+SS_Dark.Lights[id].flicker*noise(SS_Dark.Lights[id].n+ElapsedTime*2))
        end
    end
    SS_Dark.mesh:draw()
end

--shader
SS_Dark.shader={
v=[[
uniform mat4 modelViewProjection;
attribute vec4 position;
varying highp vec4 vPosition;

void main()
{
    vPosition = position;
    gl_Position = modelViewProjection * position;
}

]]
,
f=[[
precision highp float;
uniform vec4 lightPos1;  //x,y position
uniform vec4 lightPos2;  //x,y position
uniform vec4 lightPos3;  //x,y position
uniform float lightRadius1;
uniform float lightRadius2;
uniform float lightRadius3;
uniform float lightFlicker1;
uniform float lightFlicker2;
uniform float lightFlicker3;
uniform float topY;
varying highp vec4 vPosition;

void main()
{  
  highp float d=0.0;
  //fade at top of darkness
  if (topY>0.) d=clamp(1.0-distance(vPosition,vec4(vPosition.x,topY,0.0,1.0))/100.0,0.0,1.0);
  if (lightRadius1>0.0) {
    highp float f = lightRadius1 * lightFlicker1;
    d=d+clamp(1.0-distance(vPosition,lightPos1)/f+0.1,0.0,1.0);
  }
  if (lightRadius2>0.0) {
    highp float f = lightRadius2 * lightFlicker2;
    d=d+clamp(1.0-distance(vPosition,lightPos2)/f+0.1,0.0,1.0);
  }
  if (lightRadius3>0.0) {
    highp float f = lightRadius3 * lightFlicker3;
    d=d+clamp(1.0-distance(vPosition,lightPos3)/f+0.1,0.0,1.0);
  }
  gl_FragColor = vec4(0.,0.,0.,1.0-d);
}
]]
}