Spark AR: Visual Shader in JS

const Diagnostics = require('Diagnostics');
const Scene = require('Scene');
const Shaders = require('Shaders');
const Materials = require("Materials");
const R = require("Reactive");
const CameraInfo = require('CameraInfo');
const Textures = require('Textures');

const mat = Materials.get("material0");
const cameraTexture = Textures.get("cameraTexture0");
const cameraColor = cameraTexture.signal;

// get the texture coordinates in fragment stage
const texcoords = Shaders.fragmentStage(Shaders.vertexAttribute({'variableName': Shaders.VertexAttribute.TEX_COORDS}));

var color = R.pack4(1,0,0,1);

const pixelSizeX  = R.div(1,CameraInfo.previewSize.width);
const pixelSizeY = R.div(1,CameraInfo.previewSize.height);

const isHalfStep = R.step(texcoords.y, 0.5);
const isHalf = R.mix(0,1,isHalfStep);

const newUV = R.pack2(
    R.mul(R.mul(isHalf,texcoords.x),2),
    R.mul(texcoords.y,2)
);

var sampled = greaterThenSignal(texcoords.y,0.5, R.pack4(1,0,0,1), R.pack4(0,1,0,1));

//var sampled = Shaders.textureSampler(cameraColor, newUV);

// set texture to sampled
const textureSlot = Shaders.DefaultMaterialTextures.DIFFUSE
mat.setTexture(sampled, {textureSlotName: textureSlot});

function greaterThenSignal(shadersignal, value, leftSignal, rightSignal) {
    var step = R.step(shadersignal, value);
    return R.mix(leftSignal, rightSignal, step);
}