lentil/gravity
lentil/gravity
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

corrected velocity verlet

Browse Source
This commit is contained in:
Lentil Hoffman 2025-12-26 22:43:55 -06:00
parent 3b2122d2e6
commit b41d6dd488
Signed by: lentil
GPG Key ID: 0F5B99F3F4D0C087
4 changed files with 37 additions and 33 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
config.js
View File

@ -6,20 +6,21 @@ export const DISPLAY_CURRENT_MODE = false;
export const DISPLAY_VELOCITY_VECTORS = true;
export const DISPLAY_ACCELERATION_VECTORS = true;
export const MASS_CREATION_RATE = 0.001;
export const MASS_CREATION_RATE = 1E1;
export const POINTER_HISTORY_SIZE = 15;
export const VELOCITY_VECTOR_SCALE = 0.1;
export const VELOCITY_VECTOR_SCALE = 5E0;
export const VELOCITY_VECTOR_COLOR = 'rgb(150, 150, 150)'; // optionally set to 'object color'
export const VELOCITY_VECTOR_WIDTH = 1.5;
export const VELOCITY_VECTOR_ARROWHEAD = true;
export const ACCELERATION_VECTOR_SCALE = 1E-1;
export const ACCELERATION_VECTOR_SCALE = 5E0;
export const ACCELERATION_VECTOR_COLOR = 'rgb(0, 255, 0)'; // optionally set to 'object color'
// export const ACCELERATION_VECTOR_COLOR = 'object color';
export const ACCELERATION_VECTOR_WIDTH = 1.5;
export const ACCELERATION_VECTOR_ARROWHEAD = true;
export const MOTION_TIME_SCALE = 5E-5;
export const MOTION_TIME_SCALE = 1E-4;
export const PAN_VELOCITY_SCALE_FACTOR = 1E-3;
export const ARROWHEAD_LENGTH = 7;

16
display.js
View File

@ -147,10 +147,11 @@ export class Display {
// Draw arrow for the velocity
if (DISPLAY_VELOCITY_VECTORS) {
const endVx = x + VELOCITY_VECTOR_SCALE * vx;
const endVy = y + VELOCITY_VECTOR_SCALE * vy;
const speed = Math.sqrt(vx ** 2 + vy ** 2);
const endVx = x + VELOCITY_VECTOR_SCALE * vx / speed * Math.log(speed);
const endVy = y + VELOCITY_VECTOR_SCALE * vy / speed * Math.log(speed);
const style = VELOCITY_VECTOR_COLOR === 'object color' ?
ctx.fillStyle : VELOCITY_VECTOR_COLOR;
`rgb(${r}, ${g}, ${b})` : VELOCITY_VECTOR_COLOR;
this.drawArrow(x, y, endVx, endVy, {
style,
width: VELOCITY_VECTOR_WIDTH,
@ -162,10 +163,13 @@ export class Display {
// Draw arrow for acceleration
if (DISPLAY_ACCELERATION_VECTORS) {
const endAx = x + ACCELERATION_VECTOR_SCALE * acceleration.x;
const endAy = y + ACCELERATION_VECTOR_SCALE * acceleration.y;
const accelerationMagnitude = Math.sqrt(acceleration.x ** 2 + acceleration.y ** 2);
const endAx = x + ACCELERATION_VECTOR_SCALE * acceleration.x /
accelerationMagnitude * Math.log(accelerationMagnitude);
const endAy = y + ACCELERATION_VECTOR_SCALE * acceleration.y /
accelerationMagnitude * Math.log(accelerationMagnitude);
const style = ACCELERATION_VECTOR_COLOR === 'object color' ?
ctx.fillStyle : ACCELERATION_VECTOR_COLOR;
`rgb(${r}, ${g}, ${b})` : ACCELERATION_VECTOR_COLOR;
this.drawArrow(x, y, endAx, endAy, {
style,
width: ACCELERATION_VECTOR_WIDTH,

3
object.js
View File

@ -4,6 +4,7 @@ export class MassObject {
density = 1;
position = {x: undefined, y: undefined};
velocity = {x: 0, y: 0};
acceleration = {x: 0, y: 0};
color = {r: undefined, g: undefined, b: undefined};
created = undefined;
forces = []; // [{x, y}]
@ -28,7 +29,7 @@ export class MassObject {
return Math.pow(this.mass / this.density, 1/3);
}
get acceleration() {
getAcceleration() {
let ax = 0;
let ay = 0;
for (let {x, y} of this.forces) {

42
objects.js
View File

@ -114,7 +114,7 @@ export class Objects {
}
}
computeForces(elapsedTime) {
computeForces() {
if (this.objects.length < 2) return;
for (let i = 0; i < this.objects.length; i++) {
this.objects[i].forces = [];
@ -138,6 +138,7 @@ export class Objects {
}
computeFrame(elapsedTime) {
elapsedTime = elapsedTime * MOTION_TIME_SCALE;
// If we're creating an object, increment its mass
// with the mass creation rate accelerating over time
if (this.creatingObject !== undefined) {
@ -146,42 +147,39 @@ export class Objects {
obj.mass += rate * elapsedTime;
}
// Calculate forces due to gravity.
this.computeForces();
if (this.sim.playing) {
// Calculate forces due to gravity.
this.computeForces(elapsedTime);
// Generate predicted positions (Velocity verlet method)
for (let i = 0; i < this.objects.length; i++) {
const obj = this.objects[i];
obj.currentAcceleration = {...obj.acceleration};
obj.projectedPosition = {
x: obj.position.x + MOTION_TIME_SCALE * elapsedTime *
(obj.velocity.x + 1/2 * obj.currentAcceleration.x * elapsedTime),
y: obj.position.y + MOTION_TIME_SCALE * elapsedTime *
(obj.velocity.y + 1/2 * obj.currentAcceleration.y * elapsedTime),
};
obj.currentPosition = {...obj.position};
obj.position = obj.projectedPosition;
obj.currentAcceleration = obj.getAcceleration();
obj.position.x += elapsedTime *
(obj.velocity.x + 1/2 * obj.currentAcceleration.x * elapsedTime);
obj.position.y += elapsedTime *
(obj.velocity.y + 1/2 * obj.currentAcceleration.y * elapsedTime);
}
// Recompute forces
this.computeForces();
// Average first and second predicted accelerations
// Generated predicted velocities
for (let i = 0; i < this.objects.length; i++) {
const obj = this.objects[i];
const acceleration = {...obj.acceleration};
const meanAcceleration = {
const acceleration = obj.getAcceleration();
obj.acceleration = {
x: (obj.currentAcceleration.x + acceleration.x) / 2,
y: (obj.currentAcceleration.y + acceleration.y) / 2,
};
obj.velocity.x += meanAcceleration.x * MOTION_TIME_SCALE * elapsedTime;
obj.velocity.y += meanAcceleration.y * MOTION_TIME_SCALE * elapsedTime;
obj.position.x = obj.currentPosition.x + obj.velocity.x * MOTION_TIME_SCALE * elapsedTime;
obj.position.y = obj.currentPosition.y + obj.velocity.y * MOTION_TIME_SCALE * elapsedTime;
obj.velocity.x += obj.acceleration.x * elapsedTime;
obj.velocity.y += obj.acceleration.y * elapsedTime;
}
} else {
for (let i = 0; i < this.objects.length; i++) {
const obj = this.objects[i];
obj.acceleration = obj.getAcceleration();
}
}
// Display objects info