From 999a549825d3de0b53e2922462ed1e120e176ec2 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Patrick=20Sch=C3=B6nberger?= <patrick.schoenberger@posteo.de>
Date: Sat, 6 Feb 2021 12:48:25 +0100
Subject: [PATCH] simulate

---
 Scripts/cloth.js               |  90 +++++++++++++++++++++++++++++----
 Scripts/main.js                |   4 +-
 Textures/DeutschlandFlagge.jpg | Bin 0 -> 4333 bytes
 3 files changed, 83 insertions(+), 11 deletions(-)
 create mode 100644 Textures/DeutschlandFlagge.jpg

diff --git a/Scripts/cloth.js b/Scripts/cloth.js
index db07ac3..0c4f02c 100644
--- a/Scripts/cloth.js
+++ b/Scripts/cloth.js
@@ -1,14 +1,35 @@
+const DAMPING = 0.03;
+const DRAG = 1 - DAMPING;
 const MASS = 0.1;
+const GRAVITY = new THREE.Vector3(0, -9.81 * MASS, 0);
+const K = 1;
+
+let tmpCorrection;
 
 class Constraint {
-  constructor(p1, p2, distance) {
+  constructor(p1, p2, restDist) {
     this.p1 = p1;
     this.p2 = p2;
-    this.distance = distance;
+    this.restDist = restDist;
+  }
+
+  satisfy() {
+    const diff = this.p2.position.clone().sub(this.p1.position);
+    const currentDist = diff.length();
+    if (currentDist == 0) return;
+    if (currentDist <= this.restDist) return;
+    const correction = diff.multiplyScalar(1 - (this.restDist / currentDist));
+    correction.multiplyScalar(K);
+    tmpCorrection = correction;
+    const correctionHalf = correction.multiplyScalar(0.5);
+    this.p1.position.add(correctionHalf);
+    this.p2.position.sub(correctionHalf);
   }
 }
 
 class Particle {
+  movable = true;
+
   constructor(x, y, z, mass) {
     this.position = new THREE.Vector3(x, y, z);
     this.previous = new THREE.Vector3(x, y, z);
@@ -16,10 +37,23 @@ class Particle {
     this.mass = mass;
   }
   addForce(force) {
-
+    this.acceleration.add(
+      force.clone().multiplyScalar(1/this.mass)
+    );
   }
   verlet(dt) {
-
+    // verlet algorithm
+    // next position = 2 * current Position - previous position + acceleration * (passed time)^2
+    // acceleration (dv/dt) = F(net)
+    const nextPosition = this.position.clone().sub(this.previous);
+    nextPosition.multiplyScalar(DRAG);
+    nextPosition.add(this.position);
+    nextPosition.add(this.acceleration.multiplyScalar(dt*dt));
+
+    this.previous = this.position;
+    this.position = nextPosition;
+
+    this.acceleration.set(0, 0, 0);
   }
 }
 
@@ -29,6 +63,7 @@ class Cloth {
     this.height = height;
     this.numPointsWidth = numPointsWidth;
     this.numPointsHeight = numPointsHeight;
+    this.windFactor = new THREE.Vector3(0.5, 0.2, 0.2);
 
     /**
      * distance between two vertices horizontally/vertically
@@ -55,6 +90,10 @@ class Cloth {
       }
     }
 
+    this.particles[this.getVertexIndex(0, 0)].movable = false;
+    this.particles[this.getVertexIndex(0, numPointsHeight-1)].movable = false;
+    this.particles[this.getVertexIndex(numPointsWidth-1, 0)].movable = false;
+
     const REST_DIST_X = width / (numPointsWidth-1);
     const REST_DIST_Y = height / (numPointsHeight-1);
 
@@ -71,7 +110,7 @@ class Cloth {
             REST_DIST_X
           ));
         }
-        if (x < numPointsWidth-1) {
+        if (y < numPointsHeight-1) {
           this.constraints.push(new Constraint(
             this.particles[this.getVertexIndex(x, y)],
             this.particles[this.getVertexIndex(x, y+1)],
@@ -126,13 +165,44 @@ class Cloth {
     return geometry;
   }
   updateGeometry(geometry) {
-
-  }
-  satisfyConstraints() {
-
+    const positions = geometry.attributes.position.array;
+    for (let i in this.particles) {
+      let p = this.particles[i];
+      if (p.movable) {
+        positions[i*3+0] = p.position.x;
+        positions[i*3+1] = p.position.y;
+        positions[i*3+2] = p.position.z;
+      } else {
+        p.position = p.previous;
+      }
+    }
+    geometry.attributes.position.needsUpdate = true;
+    geometry.computeBoundingSphere();
+    geometry.computeVertexNormals();
   }
-  simulate() {
+  simulate(dt) {
+    let now = performance.now();
+    for (let particle of this.particles) {
+      let vertex = particle.position;
+      let fWind = new THREE.Vector3(
+        this.windFactor.x * (Math.sin(vertex.x * vertex.y * now)+1),
+        this.windFactor.y * Math.cos(vertex.z * now),
+        this.windFactor.z * Math.sin(Math.cos(5 * vertex.x * vertex.y * vertex.z))
+      );
+      // normalize then multiply?
+      particle.addForce(fWind);
+      // calculate wind with normal?
+
+      particle.addForce(GRAVITY);
+
+      particle.verlet(dt);
+    }
 
+    
+    for (let constraint of this.constraints) {
+      constraint.satisfy();
+    }
+    //console.log(tmpCorrection);
   }
   /**
    * helper function to calculate index of vertex
diff --git a/Scripts/main.js b/Scripts/main.js
index d54aa9f..3353f4d 100644
--- a/Scripts/main.js
+++ b/Scripts/main.js
@@ -98,7 +98,9 @@ function init() {
    * @param {number} dt - time passed since last frame in ms
    */
   function animate(dt) {
-    // simulate cloth
+    cloth.simulate(dt / 1000);
+
+    cloth.updateGeometry(clothGeometry);
     
     raycaster.setFromCamera( new THREE.Vector2((mousePos.x / w) * 2 - 1, ((h - mousePos.y) / h) * 2 - 1), camera );
 
diff --git a/Textures/DeutschlandFlagge.jpg b/Textures/DeutschlandFlagge.jpg
new file mode 100644
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-- 
2.50.1