michael@0: /* -*- Mode: javascript; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* vim: set ts=2 et sw=2 tw=80: */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: "use strict";
michael@0: 
michael@0: /**
michael@0:  * This worker handles picking, given a set of vertices and a ray (calculates
michael@0:  * the intersection points and offers back information about the closest hit).
michael@0:  *
michael@0:  * Used in the TiltVisualization.Presenter object.
michael@0:  */
michael@0: self.onmessage = function TWP_onMessage(event)
michael@0: {
michael@0:   let data = event.data;
michael@0:   let vertices = data.vertices;
michael@0:   let ray = data.ray;
michael@0: 
michael@0:   let intersection = null;
michael@0:   let hit = [];
michael@0: 
michael@0:   // calculates the squared distance between two points
michael@0:   function dsq(p1, p2) {
michael@0:     let xd = p2[0] - p1[0];
michael@0:     let yd = p2[1] - p1[1];
michael@0:     let zd = p2[2] - p1[2];
michael@0: 
michael@0:     return xd * xd + yd * yd + zd * zd;
michael@0:   }
michael@0: 
michael@0:   // check each stack face in the visualization mesh for intersections with
michael@0:   // the mouse ray (using a ray picking algorithm)
michael@0:   for (let i = 0, len = vertices.length; i < len; i += 36) {
michael@0: 
michael@0:     // the front quad
michael@0:     let v0f = [vertices[i],      vertices[i + 1],  vertices[i + 2]];
michael@0:     let v1f = [vertices[i + 3],  vertices[i + 4],  vertices[i + 5]];
michael@0:     let v2f = [vertices[i + 6],  vertices[i + 7],  vertices[i + 8]];
michael@0:     let v3f = [vertices[i + 9],  vertices[i + 10], vertices[i + 11]];
michael@0: 
michael@0:     // the back quad
michael@0:     let v0b = [vertices[i + 24], vertices[i + 25], vertices[i + 26]];
michael@0:     let v1b = [vertices[i + 27], vertices[i + 28], vertices[i + 29]];
michael@0:     let v2b = [vertices[i + 30], vertices[i + 31], vertices[i + 32]];
michael@0:     let v3b = [vertices[i + 33], vertices[i + 34], vertices[i + 35]];
michael@0: 
michael@0:     // don't do anything with degenerate quads
michael@0:     if (!v0f[0] && !v1f[0] && !v2f[0] && !v3f[0]) {
michael@0:       continue;
michael@0:     }
michael@0: 
michael@0:     // for each triangle in the stack box, check for the intersections
michael@0:     if (self.intersect(v0f, v1f, v2f, ray, hit) || // front left
michael@0:         self.intersect(v0f, v2f, v3f, ray, hit) || // front right
michael@0:         self.intersect(v0b, v1b, v1f, ray, hit) || // left back
michael@0:         self.intersect(v0b, v1f, v0f, ray, hit) || // left front
michael@0:         self.intersect(v3f, v2b, v3b, ray, hit) || // right back
michael@0:         self.intersect(v3f, v2f, v2b, ray, hit) || // right front
michael@0:         self.intersect(v0b, v0f, v3f, ray, hit) || // top left
michael@0:         self.intersect(v0b, v3f, v3b, ray, hit) || // top right
michael@0:         self.intersect(v1f, v1b, v2b, ray, hit) || // bottom left
michael@0:         self.intersect(v1f, v2b, v2f, ray, hit)) { // bottom right
michael@0: 
michael@0:       // calculate the distance between the intersection hit point and camera
michael@0:       let d = dsq(hit, ray.origin);
michael@0: 
michael@0:       // we're picking the closest stack in the mesh from the camera
michael@0:       if (intersection === null || d < intersection.distance) {
michael@0:         intersection = {
michael@0:           // each mesh stack is composed of 12 vertices, so there's information
michael@0:           // about a node once in 12 * 3 = 36 iterations (to avoid duplication)
michael@0:           index: i / 36,
michael@0:           distance: d
michael@0:         };
michael@0:       }
michael@0:     }
michael@0:   }
michael@0: 
michael@0:   self.postMessage(intersection);
michael@0:   close();
michael@0: };
michael@0: 
michael@0: /**
michael@0:  * Utility function for finding intersections between a ray and a triangle.
michael@0:  */
michael@0: self.intersect = (function() {
michael@0: 
michael@0:   // creates a new instance of a vector
michael@0:   function create() {
michael@0:     return new Float32Array(3);
michael@0:   }
michael@0: 
michael@0:   // performs a vector addition
michael@0:   function add(aVec, aVec2, aDest) {
michael@0:     aDest[0] = aVec[0] + aVec2[0];
michael@0:     aDest[1] = aVec[1] + aVec2[1];
michael@0:     aDest[2] = aVec[2] + aVec2[2];
michael@0:     return aDest;
michael@0:   }
michael@0: 
michael@0:   // performs a vector subtraction
michael@0:   function subtract(aVec, aVec2, aDest) {
michael@0:     aDest[0] = aVec[0] - aVec2[0];
michael@0:     aDest[1] = aVec[1] - aVec2[1];
michael@0:     aDest[2] = aVec[2] - aVec2[2];
michael@0:     return aDest;
michael@0:   }
michael@0: 
michael@0:   // performs a vector scaling
michael@0:   function scale(aVec, aVal, aDest) {
michael@0:     aDest[0] = aVec[0] * aVal;
michael@0:     aDest[1] = aVec[1] * aVal;
michael@0:     aDest[2] = aVec[2] * aVal;
michael@0:     return aDest;
michael@0:   }
michael@0: 
michael@0:   // generates the cross product of two vectors
michael@0:   function cross(aVec, aVec2, aDest) {
michael@0:     let x = aVec[0];
michael@0:     let y = aVec[1];
michael@0:     let z = aVec[2];
michael@0:     let x2 = aVec2[0];
michael@0:     let y2 = aVec2[1];
michael@0:     let z2 = aVec2[2];
michael@0: 
michael@0:     aDest[0] = y * z2 - z * y2;
michael@0:     aDest[1] = z * x2 - x * z2;
michael@0:     aDest[2] = x * y2 - y * x2;
michael@0:     return aDest;
michael@0:   }
michael@0: 
michael@0:   // calculates the dot product of two vectors
michael@0:   function dot(aVec, aVec2) {
michael@0:     return aVec[0] * aVec2[0] + aVec[1] * aVec2[1] + aVec[2] * aVec2[2];
michael@0:   }
michael@0: 
michael@0:   let edge1 = create();
michael@0:   let edge2 = create();
michael@0:   let pvec = create();
michael@0:   let tvec = create();
michael@0:   let qvec = create();
michael@0:   let lvec = create();
michael@0: 
michael@0:   // checks for ray-triangle intersections using the Fast Minimum-Storage
michael@0:   // (simplified) algorithm by Tomas Moller and Ben Trumbore
michael@0:   return function intersect(aVert0, aVert1, aVert2, aRay, aDest) {
michael@0:     let dir = aRay.direction;
michael@0:     let orig = aRay.origin;
michael@0: 
michael@0:     // find vectors for two edges sharing vert0
michael@0:     subtract(aVert1, aVert0, edge1);
michael@0:     subtract(aVert2, aVert0, edge2);
michael@0: 
michael@0:     // begin calculating determinant - also used to calculate the U parameter
michael@0:     cross(dir, edge2, pvec);
michael@0: 
michael@0:     // if determinant is near zero, ray lines in plane of triangle
michael@0:     let inv_det = 1 / dot(edge1, pvec);
michael@0: 
michael@0:     // calculate distance from vert0 to ray origin
michael@0:     subtract(orig, aVert0, tvec);
michael@0: 
michael@0:     // calculate U parameter and test bounds
michael@0:     let u = dot(tvec, pvec) * inv_det;
michael@0:     if (u < 0 || u > 1) {
michael@0:       return false;
michael@0:     }
michael@0: 
michael@0:     // prepare to test V parameter
michael@0:     cross(tvec, edge1, qvec);
michael@0: 
michael@0:     // calculate V parameter and test bounds
michael@0:     let v = dot(dir, qvec) * inv_det;
michael@0:     if (v < 0 || u + v > 1) {
michael@0:       return false;
michael@0:     }
michael@0: 
michael@0:     // calculate T, ray intersects triangle
michael@0:     let t = dot(edge2, qvec) * inv_det;
michael@0: 
michael@0:     scale(dir, t, lvec);
michael@0:     add(orig, lvec, aDest);
michael@0:     return true;
michael@0:   };
michael@0: }());