Motion Blur

Examples
1

Hi guys, I just realised that if you don’t use background() you can get neat motion blur on stuff. Most of you probably know this, so to other noobs like me, if you don’t use background, it doesn’t clear the previous drawing, and if you draw a semi-transparent rectangle over the whole screen, previous drawings will slowly fade.
An example is here:


--# Main
-- Bouncing ball

function setup()
    rectMode(CORNERS)
    ellipseMode(CENTER)
    parameter.number("blurAmount", 0, 20, function() blurAlpha = 255/(blurAmount + 1) end)
    ball = physics.body(CIRCLE, 100)
    ball.restitution = 1
    ball.x = WIDTH/2
    ball.y = HEIGHT/2
    box = physics.body(CHAIN, vec2(0,0), vec2(WIDTH,0), vec2(WIDTH,HEIGHT), vec2(0,HEIGHT), vec2(0,0))
end

function draw()
    --background(0) -- You don't actually need to have a background
    fill(0,blurAlpha)
    rect(0,0,WIDTH,HEIGHT)
    fill(255)
    ellipse(ball.x, ball.y, 200)
    physics.gravity(Gravity.x * 500, Gravity.y * 500)
end
2

Nice example. You get interesting results when you try coding things out of the ordinary.

3

@MattthewLXXIII I dug up one of my old solar system projects and added your motion blur to it. Tap the screen to cycle thru the different trail options, No trails, Full trails, and Partial trails (motion blur).

displayMode(FULLSCREEN)

function setup()
    pl={}
    table.insert(pl,planet(WIDTH/2,HEIGHT/2+50,-2.1,0))
    table.insert(pl,planet(WIDTH/2,HEIGHT/2+100,-1.74,0))
    table.insert(pl,planet(WIDTH/2,HEIGHT/2+150,-1.4,0))
    table.insert(pl,planet(WIDTH/2,HEIGHT/2+200,-1.2,0))
    table.insert(pl,planet(WIDTH/2,HEIGHT/2+250,-1.1,0))
    table.insert(pl,planet(WIDTH/2,HEIGHT/2+300,-1,0))
    table.insert(pl,planet(WIDTH/2,HEIGHT/2+350,-.94,0))
    table.insert(pl,planet(WIDTH/2,HEIGHT/2+400,-.91,0))    
    sunX=WIDTH/2
    sunY=HEIGHT/2
    sunGravity=300
    show=0
end

function draw()
    if show==0 then
        str="No trails"
        done=false
        background(0)        
    elseif show==1 and not done then
        str="Full trails"
        backingMode(RETAINED)
        done=true
    elseif show==2 then
        str="Partial trails"
        fill(0,12)
        rect(0,0,WIDTH,HEIGHT)
    end
    fill(255)
    ellipse(sunX,sunY,10)
    for a,b in pairs(pl) do
        b:calc()
        b:draw()        
    end
    text("Tap screen for next option.",WIDTH/2,HEIGHT-25)
    text(str,WIDTH/2,HEIGHT-50)
end

function touched(t)
    if t.state==BEGAN then
        show=(show+1)%3
    end
end

planet=class()

function planet:init(x,y,xv,yv)
    self.x=x
    self.y=y
    self.xVel=xv
    self.yVel=yv
end

function planet:calc()
    local d=(sunGravity/((self.x-sunX)^2+(self.y-sunY)^2)^1.5)
    self.xVel=self.xVel-((self.x-sunX)*d)
    self.yVel=self.yVel-((self.y-sunY)*d)                
    self.x=self.x+self.xVel
    self.y=self.y+self.yVel    
end

function planet:draw()
    ellipse(self.x,self.y,4)    
end
4

Hi @dave1707, thanks for your response. What happens if you use backingMode(STANDARD)? It still seems to retain the stuff that has been drawn. How does it choose whether to clear it or not?