Make an object in Focal Distance always follow an object in planeTracker

cindy · October 29, 2020, 6:24pm

Hi! Did anyone know how to make an object in Focal distance always be at the same position as an object in planeTracker? I think this can be solved with transform.applyTo() function but I am not sure how to use it as there is no sample from Spark AR document

josh_beckwith · October 31, 2020, 3:51pm

Kamen Dimitrov has a script for converting a point into screen coordinates

github.com

kamend/StickyNose-SparkAR/blob/master/scripts/script.js

const D = require('Diagnostics');
const Scene = require('Scene');
const Patches = require('Patches');
const FaceTracking = require('FaceTracking');
const Shaders = require('Shaders');
const R = require('Reactive');
const Patchers = require('Patches');
const face = FaceTracking.face(0);
const rect = Scene.root.find("rectangle0");
const cam = Scene.root.find("Camera");
const canv = Scene.root.find("canvas0");

var focalPlane = cam.focalPlane;
const camCoords = face.cameraTransform.applyTo(face.nose.tip);


var u = R.add(R.div(R.div(camCoords.x, R.div(focalPlane.width,2)),2), 0.5);
var v = R.add(R.div(R.div(camCoords.y, R.div(focalPlane.height,2)),2), 0.5);

Patches.setScalarValue("mu", u);

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cindy · November 7, 2020, 6:44pm

Thank you for your reply. I have found the solution but forgot to post it here. Seems like I can use Scene.unprojectToFocalPlane() function to get the world space from screen space

josh_beckwith · November 2, 2020, 6:49pm

Oh yeah! I forgot about that one! I haven’t had a chance to use it yet, but I’m glad they added it to the API.