代码来源于openprocessing，考虑到国内不是很好访问，我把我找到的比较好的搬运过来！

合集

参考：https://openprocessing.org/sketch/793375
https://github.com/SourceOf0-HTML/processing-p5.js/tree/master

这个可以体验6种笔触，作者介绍如下：

There are multiple pages. Use the “←” “→” buttons below to switch.
The second page explains the UI.
I will explain the sketches I made in the past.
Some variable names have been changed. I wanted to explain in order, so I divided the processing in detail. The UI has been added so the code is getting longer …
Video of this sketch in action (Twitter)
https://twitter.com/BUN_information/status/1195300719231791104

Gorilla Sun has written an explanation of each part with animations on his blog. Thank you!
https://gorillasun.de/blog/Simulating-brush-strokes-with-Hookes-Law-in-P5JS-and-Processing

其中三种种笔触的代码如下：

笔触4

原笔触代码地址：https://openprocessing.org/sketch/748836

特点：越快越粗，很适合画速写。

代码

/*
setup=()=>{m=n=x=y=u=v=0,s=0.08,f=0.8;createCanvas(L=500,L);background(C=255)}
draw=()=>{u+=(m-x)*s,v+=(n-y)*s,u*=f,v*=f,a=x,b=y;strokeWeight(abs(u+v)/3+1);line(x+=u,y+=v,a,b)}
mousePressed=()=>{x=m=mouseX,y=n=mouseY}
mouseDragged=()=>{m=mouseX,n=mouseY}
/**/

function setup() {
  mX = mY = x = y = ax = ay = 0;
  spring = 0.08;
  friction = 0.8;
  createCanvas( 500, 500 );
  background( 255 );
}

function draw() {
  ax += ( mX - x ) * spring;
  ay += ( mY - y ) * spring;
  ax *= friction;
  ay *= friction;
  
  oldX = x;
  oldY = y;
  x += ax;
  y += ay;
  strokeWeight( abs( ax + ay ) / 3 + 1 );
  line( x, y, oldX, oldY );
}

function mousePressed() {
  mX = x = mouseX;
  mY = y = mouseY;
}

function mouseDragged() {
  mX = mouseX;
  mY = mouseY;
}

笔触5

原笔触代码地址：https://openprocessing.org/sketch/754815

特点：越慢越粗，墨水有晕染感，适合写字。

/*
setup=_=>createCanvas(S=500,S),D=10,m=n=x=y=u=v=r=f=0
draw=_=>{R=r;if(mouseIsPressed){m=mouseX;n=mouseY;!f?(f=1,x=m,y=n):0;u+=(m-x)/2;v+=(n-y)/2;u/=2;v/=2;r=25-sqrt(u*u+v*v)*.7;i=D;while(--i)strokeWeight(R+=(r-R)/D),line(x,y,x+=u/D,y+=v/D)}else if(f){u=v=f=0}}
/**/

function setup() {
  createCanvas(S=500,S);
  distance = 10;
  spring = 0.5;
  friction = 0.5;
  mX = mY = x = y = ax = ay = r = f = 0;
}

function draw() {
  oldR = r;
  if(mouseIsPressed) {
    mX = mouseX;
    mY = mouseY;
    if(!f) {
      f = 1;
      x = mX;
      y = mY;
    }
    ax += ( mX - x ) * spring;
    ay += ( mY - y ) * spring;
    ax *= friction;
    ay *= friction;
    r = 25 - sqrt( ax*ax + ay*ay ) * 0.7;
  
    for( i = 0; i < distance; ++i ) {
      oldX = x;
      oldY = y;
      x += ax / distance;
      y += ay / distance;
      oldR += ( r - oldR ) / distance;
      strokeWeight( oldR );
      line( x, y, oldX, oldY );
    }
  } else if(f) {
    ax = ay = f = 0;
  }
}
/**/

笔触6

原笔触代码地址：https://openprocessing.org/sketch/755877

特点：越慢越粗，有墨水晕染，线条有割裂，适合写毛笔字。

/**
 * Added on October 22, 2020
 * 
 * Hi, I'm BUN.
 * I've been surprised at how many people have forked over this sketch, more than I expected. Thanks.
 * 
 * Here is a sketch that explains this code with multiple codes.
 * Please use it as a reference.
 * https://www.openprocessing.org/sketch/793375
 * 
 * Brief explanation.
 * This code primarily uses "Hook's Law".
 * In other words, it simulates the motion of a spring.
 * 
 * From the mouse position, the position to be drawn is moved like a spring.
 * And the width of the line is changed according to the speed of the movement.
 * 
 ** Added on May 8, 2021 **
 * Gorilla Sun has written an explanation of each part with animations on his blog. Thank you!
 * https://gorillasun.de/blog/Simulating-brush-strokes-with-Hooke's-Law-in-P5JS-and-Processing
 **/
function setup() {
  createCanvas(windowWidth,windowHeight);
  distance = 10;
  spring = 0.5;
  friction = 0.5;
  size = 25;
  diff = size/8;
  x = y = ax = ay = a = r = f = 0;
}

function draw() {
  oldR = r;
  if(mouseIsPressed) {
    mX = mouseX;
    mY = mouseY;
    if(!f) {
      f = 1;
      x = mX;
      y = mY;
    }
    ax += ( mX - x ) * spring;
    ay += ( mY - y ) * spring;
    ax *= friction;
    ay *= friction;
    a += sqrt( ax*ax + ay*ay ) - a;
    a *= 0.6;
    r = size - a;
    
    for( i = 0; i < distance; ++i ) {
      oldX = x;
      oldY = y;
      x += ax / distance;
      y += ay / distance;
      oldR += ( r - oldR ) / distance;
      if(oldR < 1) oldR = 1;
      strokeWeight( oldR+diff );
      line( x, y, oldX, oldY );
      strokeWeight( oldR );
      line( x+diff*2, y+diff*2, oldX+diff*2, oldY+diff*2 );
      line( x-diff, y-diff, oldX-diff, oldY-diff );
    }
  } else if(f) {
    ax = ay = f = 0;
  }
}
/**/