Ripple V3

--[[local function getY( centerx, centery, radius, x )
    local origin = math.sqrt( radius^2 - (x - centerx) ^2 )
    return math.floor(centery + origin), math.floor(centery - origin)
end
]]

local tCircles = {}
local function drawCircle( centerX, centerY, radius, col, solid )
    solid = solid or false
    local isAdvanced = term.isColor and term.isColor()
    local char = isAdvanced and " " or "|"
    if isAdvanced then term.setBackgroundColor( col ) end
    local radStep = 1/(1.5*radius)
    for angle = 1, math.pi+radStep, radStep do
        local pX = math.cos( angle ) * radius * 1.5
        local pY = math.sin( angle ) * radius
        if solid then
            local chord = 2*math.abs(pX)
            term.setCursorPos( centerX - chord/2, centerY - pY )
            write( char:rep( chord ) )
            term.setCursorPos( centerX - chord/2, centerY + pY )
            write( char:rep( chord ) )
        else
            for i=-1,1,2 do
                for j=-1,1,2 do
                    term.setCursorPos( centerX + i*pX, centerY + j*pY )
                    write( char )
                end
            end
        end
    end
end

local tWindows = { ["term"] = window.create( term.current(), 1, 1, term.getSize() ) }

local id = os.startTimer( 0.1 )

while true do
    local event = { os.pullEvent() }
    if event[ 1 ] == "mouse_click" then
        tCircles[ #tCircles + 1 ] = { parent = "term", r = 1, x = event[ 3 ], y = event[ 4 ] }
    elseif event[ 1 ] == "monitor_touch" then
        if not tWindows[ event[ 2 ] ] then
            peripheral.call( event[ 2 ], "setTextScale", 0.5 )
            tWindows[ event[ 2 ] ] = window.create( peripheral.wrap( event[ 2 ] ), 1, 1, peripheral.call( event[ 2 ], "getSize" ) )
        end
        tCircles[ #tCircles + 1 ] = { parent = event[ 2 ], r = 1, x = event[ 3 ], y = event[ 4 ] }
    elseif event[ 1 ] == "timer" and event[ 2 ] == id then
        id = os.startTimer( 0.1 )
        for k, v in pairs( tWindows ) do
            v.setVisible( false )
            v.setBackgroundColor( colors.lightBlue )
            v.clear()
        end
        local origin = term.current()
        for i, circle in pairs( tCircles ) do
            local t = tWindows[ circle.parent ]
            local maxx, maxy = t.getSize()
            term.redirect( t )
            --[[
            for x = 1, maxx, 0.75 / circle.r do
                local y1, y2 = getY( circle.x, circle.y, circle.r, x )
                t.setCursorPos( x, y1 )
                t.write( " " )
                t.setCursorPos( x, y2 )
                t.write( " " )
            end
            ]]--
            drawCircle( circle.x, circle.y, circle.r, colors.blue, false )
            circle.r = circle.r + 1
            if circle.r > ( maxx / 2 ) then
                table.remove( tCircles, i )
            end
        end
        term.redirect( origin )
        for _, v in pairs( tWindows ) do
            v.setVisible( true )
            v.redraw()
        end
    end
end