Your first project

entelechy new <dir> writes a directory that runs: a Kernel, the scene that places it, a replay that checks what it draws, and a README saying what to change first.

entelechy new hello

play it:  entelechy player hello/scene.esn
run it:   entelechy run hello/scene.esn --window 640x400 --out frame.png
test it:  entelechy replay hello/tests/hello.replay

--kind picture|sound|game picks the start (a picture by default).

What it writes

hello/
├── README.md
├── scene.esn          the scene: nodes, params, outputs
├── kernels/
│   └── hello.ent      the Kernel: what each pixel computes
└── tests/
    └── hello.replay   the replay: a pixel's color at a frame

scene.esn: one node over the window.

// One node: the Kernel over a window's worth of pixels.
use "kernels/";

param rate: Float = 0.35;

node picture: hello.draw@1 { rate = rate; domain = window(); }

output result <- picture.result;

kernels/hello.ent: each pixel works out its color from where it is and what time it is.

kernel hello.draw@1 {
    requires { field.write; time.read; }
    param rate: Float = 0.35;             // how fast the colors turn
    output result: Image;
    compute {
        // Where this pixel is, from -1 to 1 across the shorter side.
        let { x: width, y: height } = domain();
        let place = (coord() * 2.0 - domain()) / min(width, height);
        let away = length(place);
        let turn = time() * rate;
        // Rings that move outwards, and a color that goes round.
        let ring = sin(away * 8.0 - turn * 6.2831853) * 0.5 + 0.5;
        let color = mix(
            vec3(0.15, 0.25, 0.45),
            vec3(0.95, 0.65, 0.35),
            ring * saturate(1.2 - away)
        );
        return vec4(color, 1.0);
    }
}

Note requires { field.write; time.read; }: reading the clock needs the time.read capability. See Capabilities & security.

tests/hello.replay:

scene ../scene.esn

# A small window, so the pixels are few and the test is quick.
window 64 40 1
frame 0.0
expect 32 20 = 0.550 0.450 0.400 0.01
frame 0.5
expect 32 20 = 0.194 0.272 0.445 0.01

Run it

entelechy player hello/scene.esn                              # a window (needs entelechy-player)
entelechy run hello/scene.esn --window 640x400 --out frame.png  # no window, one picture
entelechy replay hello/tests/hello.replay                     # the test

Edit kernels/hello.ent while the Player is open and the picture changes as you save; a Kernel that does not compile leaves the running one alone and says why.

Try next

The README suggests two exercises:

1. Give the scene another param and use it in the Kernel.
2. Add a second node that reads the first (input under: Image; and sample(under)) to draw over it.

Next, write a Kernel from scratch: Your first Kernel.