FPS Plotter and FPS Radar: experiments with DeltaTime

Code Sharing
1

I thought I detected a stutter in DeltaTime when beta testing Codea, and wrote the code below to examine it (DeltaTime) graphically. Try changing the size of the Output pane while it is running.


-- 
-- FPS Plotter
--
supportedOrientations(LANDSCAPE_ANY)
backingMode(RETAINED)
function setup()
    maxDeltaTime = 1/60
    odt = 1
    dim = math.min(WIDTH, HEIGHT) * 0.5
    ox = (WIDTH - dim)/2
    oy = (HEIGHT - dim)/2
    background(0)
    strokeWidth(5)
    stroke(0, 127, 0)
    noFill()
    line(0, oy + dim/2, WIDTH, oy + dim/2)
    line(ox + dim/2, 0, ox + dim/2, HEIGHT)
    rect(ox, oy, dim, dim)
    fill(0, 255, 0)
    text("0, 0", ox - 10, oy - 10)
    text("30, 0", ox + dim/2, oy - 10)
    text("60, 0", ox + dim + 10, oy - 10)
    text("0, 30", ox - 30, oy + dim/2)
    text("60, 30", ox + dim + 30, oy + dim/2)
    text("0, 60", ox - 10, oy + dim + 10)
    text("30, 60", ox + dim/2, oy + dim + 10)
    text("60, 60", ox + dim + 10, oy + dim + 10)
    fill(255, 64)
    noStroke()
end

function draw()
    dt = maxDeltaTime/DeltaTime
 -- print(dt) -- Uncomment to see effect of print in draw()
    ellipse(ox + dim * dt, oy + dim * odt, 10)
    odt = dt
end
2

‘FPS Radar’ below is another such experiment. Try touching in the empty Output pane and then dragging anywhere to cause draw() to be skipped while EllapsedTime marches on. Also, on my iPad2, I can create a dip (red) and spike (green) that then repeats once a second.


--
-- FPS Radar
--
supportedOrientations(LANDSCAPE_ANY)
backingMode(RETAINED)
function setup()
    background(0)
    dim = math.min(WIDTH, HEIGHT) * 0.5 / 2
    cx = WIDTH/2
    cy = HEIGHT/2
    maxDeltaTime = 1/60
    twoPi = 2 * math.pi
    parameter("dummy") -- Just for experimentation
end

function draw()
    local a = ElapsedTime * twoPi
    local ratio = maxDeltaTime/DeltaTime
    local radius = ratio * dim
    fill(0, 10)
    noStroke()
    rect(0, 0, WIDTH, HEIGHT)
    local r = 255
    local g = 255
    local b = 255
    if ratio > 1.1 then r = 0; b = 0 end
    if ratio < 0.9 then g = 0; b = 0 end
    stroke(r, g, b)
    strokeWidth(10)
    line(cx, cy, cx + math.cos(a) * radius, cy + math.sin(a) * radius)
end
3

Hi @mpilgrem, dragging or scrolling from the text output has paused my programs from the beginning I think. I actually got used to it and used it as an easier-to-hit pause… But I suppose it shouldn’t be that way! :slight_smile:

I like the visualisations!

4

This inspired me to add some frame rate history to my frame rate library. When I develop animations, I often see some jerky movements. I was not able to break down from where it comes, but with the frame rate history, I could now see it → It only happens, when started in standard mode. When I start in full screen, then the framerate is always ok. When started in standard mode, the framerate drops every 5th or so frame. When playing around with the parameters and scrolling in the print output (although its empty), suddenly the problems are gone.

Have a look at the two screenshots, the first with the jerky movement, the second with normal movement. The framerate is shown for the last 100 frames as vertical bars from red to green:

https://dl.dropbox.com/u/80475380/CodeaForumPictures/framerate_jerky.JPG

https://dl.dropbox.com/u/80475380/CodeaForumPictures/framerate_stable.JPG