Animation helper functions

Luxor provides some functions to help you create animations—at least, it provides some assistance in creating lots of individual frames that can later be stitched together to form a moving animation, such as a GIF or MP4.

There are four steps to creating an animation.

1 Use Movie to create a Movie object which determines the title and dimensions.

2 Define some functions that draw the graphics for specific frames.

3 Define one or more Scenes that call these functions for specific frames.

4 Call the animate(movie::Movie, scenes) function, passing in the scenes. This creates all the frames and saves them in a temporary directory. ffmpeg can build an animated GIF from the frames.

Example

demo = Movie(400, 400, "test")

function backdrop(scene, framenumber)
    background("black")
end

function frame(scene, framenumber)
    sethue(Colors.HSV(framenumber, 1, 1))
    eased_n = scene.easingfunction(framenumber, 0, 1, scene.framerange.stop)
    circle(polar(100, -π/2 - (eased_n * 2π)), 80, :fill)
    text(string("frame $framenumber of $(scene.framerange.stop)"),
        Point(O.x, O.y-190),
        halign=:center)
    text(scene.opts,
        boxbottomcenter(BoundingBox()),
        halign=:center,
        valign=:bottom)
end

animate(demo, [
    Scene(demo, backdrop, 0:359),
    Scene(demo, frame, 0:359,
        easingfunction=easeinoutcubic,
        optarg="made with Julia")
    ],
    creategif=true)

In this example, the movie uses two scenes, each specifying a function to draw frames from 0 to 359. For each frame numbered 0 to 359, the graphics are drawn by both the backdrop and frame functions, in that order. A drawing is automatically created (in PNG format) and centered (origin) so you can start drawing immediately. The finish function is automatically called when all the drawing functions in the scenes have completed, and the process starts afresh for the next frame. The second scene, calling the frame function, shows how you can pass optional information to the function.

Making the animation

You can build animations automatically using ffmpeg. The creategif option for the animate function runs ffmpeg when the frames have all been generated.

Inside animate, the first pass creates a GIF color palette, the second builds the file:

run(`ffmpeg -f image2 -i $(tempdirectory)/%10d.png -vf palettegen
    -y $(seq.stitle)-palette.png`)

run(`ffmpeg -framerate 30 -f image2 -i $(tempdirectory)/%10d.png
    -i $(seq.stitle)-palette.png -lavfi paletteuse -y /tmp/$(seq.stitle).gif`)

Many movie editing programs, such as Final Cut Pro, will also let you import sequences of still images into a movie timeline.

ffmpeg has literally hundreds of options, which include codec selection, framerate adjustment and color palette tweaking. If you want to use a custom ffmpeg command, you can use code such as this:

using Luxor, FFMPEG

...

# store the frames in a temp directory
tempdirectory = "/tmp/temp/"

animate(movie, [
        Scene(movie, frame, 1:50)
    ], 
    creategif=false, # don't have to create the GIF here
    tempdirectory=tempdirectory)

# run a custom ffmpeg command
FFMPEG.ffmpeg_exe(`-r 30 -f image2 -i $(tempdirectory)/%10d.png -c:v libx264 -r 30 -pix_fmt yuv420p -y /tmp/animation.mp4`)

Passing information to the frame() function

If you want to pass information to the frame function, such as an array of values, try these two approaches.

Either, call the enhanced frame() function with extra arguments with (s, f) -> frame(s, f, databuffer):

function frame(scene, framenumber, databuffer)
    eased_n = scene.easingfunction(framenumber - scene.framerange.start,
        0, 1, scene.framerange.stop - scene.framerange.start)
    w = size(databuffer, 1)
    h = size(databuffer, 2)
    for c in 1:w, r in 1:h
        rs = rescale(r, 1, h, 0, 2π)
        cs = rescale(c, 1, h, 0, 2π)
        databuffer[r, c] = HSV(360((sin(2rs) * cos(2cs)) * sin(eased_n * 2π)), 0.7, 0.7)
    end
    placeimage(databuffer, Point(-w / 2, -h / 2))
end

function main()
    databuffer = zeros(ARGB32, 250, 250)
    demo = Movie(250, 250, "buffer")
    animate(demo, [
            Scene(demo, (s, f) -> frame(s, f, databuffer),
                0:100)
        ],
        tempdirectory="/tmp/tempdir",
        creategif=true, 
        pathname="/tmp/t.gif")
end

Or, use the optarg keyword argument for Scene(), and access it using scene.opts keyword.

function frame(scene, framenumber)
    databuffer = scene.opts
    eased_n = scene.easingfunction(framenumber - scene.framerange.start,
        0, 1, scene.framerange.stop - scene.framerange.start)
    w = size(databuffer, 1)
    h = size(databuffer, 2)
    for c in 1:w, r in 1:h
        rs = rescale(r, 1, h, 0, 2π)
        cs = rescale(c, 1, h, 0, 2π)
        databuffer[r, c] = HSV(360((sin(2rs) * cos(2cs)) * sin(eased_n * 2π)), 0.7, 0.7)
    end
    placeimage(databuffer, Point(-w / 2, -h / 2))
end

function main()
    databuffer = zeros(ARGB32, 250, 250)
    demo = Movie(250, 250, "buffer")
    animate(demo, [Scene(demo, frame, optarg=databuffer, 0:100)],
        tempdirectory="/tmp/tempdir",
        creategif=true,
        pathname="/tmp/t.gif")
end

Animating paths

A useful function to help with animations is drawpath. This has a method that accepts a value between 0 and 1 that draws a portion of a Path object.

For example, the purple stroke is about half the length of the path.

fontsize(300)
textpath("s", O, halign=:center, valign=:middle)
s = storepath()
drawpath(s, action=:stroke)

sethue("purple")
setline(10)
setopacity(0.5)
pt = drawpath(s, 0.5, action=:stroke) # return final pt

setcolor("red")
circle(pt, 5, :fill)

It's also useful for animating text paths.

which uses code like this:

...
f =  # a value between 0 and 1
textpath("Thank you for using", pt, halign=:center)
tp = storepath()
drawpath(tp, f, :stroke)
...

Easing functions

Transitions for animations often use non-constant and non-linear motions, and these are usually provided by easing functions. Luxor defines some of the basic easing functions and they're listed in the (unexported) array Luxor.easingfunctions. Each scene can have one easing function.

Most easing functions have names constructed like this:

ease[in|out|inout][expo|circ|quad|cubic|quart|quint]

and there's an easingflat linear transition.

function draweasingfunction(f, pos, w, h)
    @layer begin
        translate(pos)
        setline(0.5)
        sethue("black")
        box(O, w, h, :stroke)
        sethue("purple")
        for i in 0:0.005:1.0
            circle(Point(-w/2, h/2) + Point(w * i, -f(i, 0, h, 1)), 1, :fill)
        end
        sethue("black")
        text(replace(string(f), "Luxor." => ""), Point(0, h/2 - 20), halign=:center)
    end
end

t = Tiler(650, 650, 5, 5)
margin=5
fontsize(10)
fontface("JuliaMono-Regular")
for (pos, n) in t
    n > length(Luxor.easingfunctions) && continue
    draweasingfunction(Luxor.easingfunctions[n], pos,
        t.tilewidth-margin, t.tileheight-margin)
end

In these graphs, the horizontal axis is time (between 0 and 1), and the vertical axis is the parameter value (between 0 and 1).

One way to use an easing function in a frame-making function is like this:

function moveobject(scene, framenumber)
    background("white")
    ...
    easedframenumber = scene.easingfunction(framenumber, 0, 1, scene.framerange.stop)
    ...

This takes the current frame number, compares it with the end frame number of the scene, then adjusts it.

In the next example, the purple dot has sinusoidal easing motion, the green has cubic, and the red has quintic. They all traverse the drawing extent in the same time, but have different accelerations and decelerations.

fastandfurious = Movie(400, 100, "easingtests")
backdrop(scene, framenumber) =  background("black")
function frame1(scene, framenumber)
    sethue("purple")
    eased_n = scene.easingfunction(framenumber, 0, 1, scene.framerange.stop)
    circle(Point(-180 + (360 * eased_n), -20), 10, :fill)
end
function frame2(scene, framenumber)
    sethue("green")
    eased_n = scene.easingfunction(framenumber, 0, 1, scene.framerange.stop)
    circle(Point(-180 + (360 * eased_n), 0), 10, :fill)
end
function frame3(scene, framenumber)
    sethue("red")
    eased_n = scene.easingfunction(framenumber, 0, 1, scene.framerange.stop)
    circle(Point(-180 + (360 * eased_n), 20), 10, :fill)
end
animate(fastandfurious, [
    Scene(fastandfurious, backdrop, 0:200),
    Scene(fastandfurious, frame1,   0:200, easingfunction=easeinsine),
    Scene(fastandfurious, frame2,   0:200, easingfunction=easeinoutcubic),
    Scene(fastandfurious, frame3,   0:200, easingfunction=easeinoutquint)
    ],
    creategif=true)

Here's the definition of one of the easing functions:

function easeoutquad(t, b, c, d)
    t /= d
    return -c * t * (t - 2) + b
end

Here:

• t is the current time (framenumber) of the transition

• b is the beginning value of the property

• c is the change between the beginning and destination value of the property

• d is the total length of the transition

The easeinoutbezier function accepts two additional arguments, two normalized control points of a normalized Bezier curve from Point(0, 0) to Point(1, 1). You can use these to define the shape of a custom easing transition. The Bezier curve's y coordinate determines the acceleration. [?]