Grass like smoothing animation on beziercurve?

问题:

This is what I am trying to achieve--GRASS Animation(Desired animation)

This is where the project is standing currently --My hair animation

This is a more structurised code of the above code --My hair animation(by markE)--markE`s code of hair animation

PROBLEM:--

I am able to give movements to hairs but animation should be more like wavy grass like freeflowing.Its not very smooth now.What can be done to make the hairs flow in more natural manner. Please provide me with a small sample if possible!!!

    <canvas id="myCanvas" width="500" height="500" style="background-color: antiquewhite" ></canvas>

JAVASCRIPT

//mouse position
var x2=0;
var y2=0;

window.addEventListener("mousemove",function(){moving(event);init()},false)

//these variables define the bend in our bezier curve
var bend9=0;
var bend8=0;
var bend7=0;
var bend6=0;
var bend5=0;
var bend4=0;
var bend3=0;
var bend2=0;
var bend1=0;

//function to get the mouse cordinates
function moving(event) {
    bend_value();//this function is defined below
    try
    {
        x2 = event.touches[0].pageX;
        y2 = event.touches[0].pageY;
    }
    catch (error)
    {
        try
        {
            x2 = event.clientX;
            y2 = event.clientY;
        }
        catch (e)
        {
        }
    }

    try
    {
        event.preventDefault();
    }
    catch (e)
    {
    }
    if(between(y2,204,237) && between(x2,115,272))
    {
    console.log("Xmove="+x2,"Ymove="+y2)
    }

}

//function for declaring range of bezier curve
function between(val, min, max)
{
    return val >= min && val <= max;
}

(function() {
    hair = function() {
        return this;
    };

    hair.prototype={

     draw_hair:function(a,b,c,d,e,f,g,h){

            var sx  =136+a;//start position of curve.used in moveTo(sx,sy)
            var sy  =235+b;
            var cp1x=136+c;//control point 1
            var cp1y=222+d;
            var cp2x=136+e;//control point 2
            var cp2y=222+f;
            var endx=136+g;//end points
            var endy=210+h;

         var canvas = document.getElementById('myCanvas');
         var context = canvas.getContext('2d');
//         context.clearRect(0, 0,500,500);
         context.strokeStyle="grey";
         context.lineWidth="8";
         context.beginPath();
         context.moveTo(sx,sy);
         context.bezierCurveTo(cp1x,cp1y,cp2x,cp2y,endx,endy);
         context.lineCap = 'round';
         context.stroke();
//         context.restore();
//         context.save();
    }
};
})();

//this function provides and calculate the bend on mousemove
function bend_value(){
    var ref1=135;//this is ref point for  hair or curve no 1
    var ref2=150;//hair no 2 and so on
    var ref3=165;
    var ref4=180;
    var ref5=195;
    var ref6=210;
    var ref7=225;
    var ref8=240;
    var ref9=255;
if(between(x2,115,270) && between(y2,205,236))
{
    if(x2>=135 && x2<=145){bend1=(x2-ref1)*(2.2);}
    if(x2<=135 && x2>=125){bend1=(x2-ref1)*(2.2);}

    if(x2>=150 && x2<=160){bend2=(x2-ref2)*(2.2);}
    if(x2<=150 && x2>=140){bend2=(x2-ref2)*(2.2);}

    if(x2>=165 && x2<=175){bend3=(x2-ref3)*(2.2);}
    if(x2<=165 && x2>=155){bend3=(x2-ref3)*(2.2);}

    if(x2>=180 && x2<=190){bend4=(x2-ref4)*(2.2);}
    if(x2<=180 && x2>=170){bend4=(x2-ref4)*(2.2);}

    if(x2>=195 && x2<=205){bend5=(x2-ref5)*(2.2);}
    if(x2<=195 && x2>=185){bend5=(x2-ref5)*(2.2);}

    if(x2>=210 && x2<=220){bend6=(x2-ref6)*(2.2);}
    if(x2<=210 && x2>=200){bend6=(x2-ref6)*(2.2);}

    if(x2>=225 && x2<=235){bend7=(x2-ref7)*(2.2);}
    if(x2<=225 && x2>=215){bend7=(x2-ref7)*(2.2);}

    if(x2>=240 && x2<=250){bend8=(x2-ref8)*(2.2);}
    if(x2<=240 && x2>=230){bend8=(x2-ref8)*(2.2);}

    if(x2>=255 && x2<=265){bend9=(x2-ref9)*(2.2);}
    if(x2<=255 && x2>=245){bend9=(x2-ref9)*(2.2);}
    }
}

function init(){//this function draws each hair/curve
    var canvas = document.getElementById('myCanvas');
    var context = canvas.getContext('2d');
    var clear=context.clearRect(0, 0,500,500);
    var save=context.save();

//   /* console.log("bend2="+bend2)
//    console.log("bend3="+bend3)
//    console.log("bend4="+bend4)
//    console.log("bend5="+bend5)
//    console.log("bend6="+bend6)
//    console.log("bend7="+bend7)
//    console.log("bend8="+bend8)
//    console.log("bend9="+bend9)*/

    hd1 = new hair();//hd1 stands for hair draw 1.this is an instance created for drawing hair no 1
    clear;
    hd1.draw_hair(0,0,0,0,0,0,0+bend1/2,0);//these parameters passed to function drawhair and bend is beint retrieved from function bend_value()
    save;

    hd2 = new hair();
    clear;
    hd2.draw_hair(15,0,15,0,15,0,15+bend2/2,0);
    save;

    hd3 = new hair();
    clear;
    hd3.draw_hair(30,0,30,0,30,0,30+bend3/2,0);
    save;

    hd4 = new hair();
    clear;
    hd4.draw_hair(45,0,45,0,45,0,45+bend4/2,0);
    save;

    hd5 = new hair();
    clear;
    hd5.draw_hair(60,0,60,0,60,0,60+bend5/2,0);
    save;
 }

window.onload = function() {
    init();
    disableSelection(document.body)
}

function disableSelection(target){
    if (typeof target.onselectstart!="undefined") //IE
        target.onselectstart=function(){return false}
    else if (typeof target.style.MozUserSelect!="undefined") //Firefox
        target.style.MozUserSelect="none"
    else //All other ie: Opera
        target.onmousedown=function(){return false}
    target.style.cursor = "default"
}

回答1:

Update: I'm currently adjusting the code to produce the requested result and commenting it.

(function() { // The code is encapsulated in a self invoking function  to isolate the scope
  "use strict";

   // The following lines creates shortcuts to the constructors of the Box2D types used
   var B2Vec2 = Box2D.Common.Math.b2Vec2,
      B2BodyDef = Box2D.Dynamics.b2BodyDef,
      B2Body = Box2D.Dynamics.b2Body,
      B2FixtureDef = Box2D.Dynamics.b2FixtureDef,
      B2Fixture = Box2D.Dynamics.b2Fixture,
      B2World = Box2D.Dynamics.b2World,
      B2PolygonShape = Box2D.Collision.Shapes.b2PolygonShape,
      B2RevoluteJoint = Box2D.Dynamics.Joints.b2RevoluteJoint,
      B2RevoluteJointDef = Box2D.Dynamics.Joints.b2RevoluteJointDef;

  // This makes sure that there is a method to request a callback to update the graphics for next frame
  window.requestAnimationFrame =
    window.requestAnimationFrame || // According to the standard
    window.mozRequestAnimationFrame || // For mozilla
    window.webkitRequestAnimationFrame || // For webkit
    window.msRequestAnimationFrame || // For ie
    function (f) { window.setTimeout(function () { f(Date.now()); }, 1000/60); }; // If everthing else fails

  var world = new B2World(new B2Vec2(0, -10), true), // Create a world with gravity
      physicalObjects = [], // Maintain a list of the simulated objects
      windInput = 0, // The input for the wind in the current frame
      wind = 0, // The current wind (smoothing the input values + randomness)
      STRAW_COUNT = 10, // Number of straws
      GRASS_RESET_SPEED = 2, // How quick should the straw reset to its target angle
      POWER_MOUSE_WIND = 120, // How much does the mouse affect the wind
      POWER_RANDOM_WIND = 180; // How much does the randomness affect the wind

  // GrassPart is a prototype for a piece of a straw. It has the following properties
  //  position: the position of the piece
  //  density: the density of the piece
  //  target: the target angle of the piece
  //  statik: a boolean stating if the piece is static (i.e. does not move)
  function GrassPart(position, density, target, statik) {
    this.width = 0.05;
    this.height = 0.5;
    this.target = target;

    // To create a physical body in Box2D you have to setup a body definition
    // and create at least one fixture.
    var bdef = new B2BodyDef(), fdef = new B2FixtureDef();
    // In this example we specify if the body is static or not (the grass roots 
    // has to be static to keep the straw in its position), and its original
    // position.
    bdef.type = statik? B2Body.b2_staticBody : B2Body.b2_dynamicBody;
    bdef.position.SetV(position);

    // The fixture of the piece is a box with a given density. The negative group index
    // makes sure that the straws does not collide.
    fdef.shape = new B2PolygonShape();
    fdef.shape.SetAsBox(this.width/2, this.height/2);
    fdef.density = density;
    fdef.filter.groupIndex = -1;

    // The body and fixture is created and added to the world
    this.body = world.CreateBody(bdef);
    this.body.CreateFixture(fdef);
  }

  // This method is called for every frame of animation. It strives to reset the original
  // angle of the straw (the joint). The time parameter is unused here but contains the
  // current time.
  GrassPart.prototype.update = function (time) {
    if (this.joint) {
      this.joint.SetMotorSpeed(GRASS_RESET_SPEED*(this.target - this.joint.GetJointAngle()));
    }
  };

  // The link method is used to link the pieces of the straw together using a joint
  // other: the piece to link to
  // torque: the strength of the joint (stiffness)
  GrassPart.prototype.link = function(other, torque) {
    // This is all Box2D specific. Look it up in the manual.
    var jdef = new B2RevoluteJointDef();
    var p = this.body.GetWorldPoint(new B2Vec2(0, 0.5)); // Get the world coordinates of where the joint
    jdef.Initialize(this.body, other.body, p);
    jdef.maxMotorTorque = torque;
    jdef.motorSpeed = 0;
    jdef.enableMotor = true;

    // Add the joint to the world
    this.joint = world.CreateJoint(jdef);
  };

  // A prototype for a straw of grass
  // position: the position of the bottom of the root of the straw
  function Grass(position) {
    var pos = new B2Vec2(position.x, position.y);
    var angle = 1.2*Math.random() - 0.6; // Randomize the target angle

    // Create three pieces, the static root and to more, and place them in line.
    // The second parameter is the stiffness of the joints. It controls how the straw bends.
    // The third is the target angle and different angles are specified for the pieces.
    this.g1 = new GrassPart(pos, 1, angle/4, true); // This is the static root
    pos.Add(new B2Vec2(0, 1));
    this.g2 = new GrassPart(pos, 0.75, angle);
    pos.Add(new B2Vec2(0, 1));
    this.g3 = new GrassPart(pos, 0.5);

    // Link the pieces into a straw
    this.g1.link(this.g2, 20);
    this.g2.link(this.g3, 3);

    // Add the pieces to the list of simulate objects
    physicalObjects.push(this.g1);
    physicalObjects.push(this.g2);
    physicalObjects.push(this.g3);
  }

  Grass.prototype.draw = function (context) {
      var p = new B2Vec2(0, 0.5);
      var p1 = this.g1.body.GetWorldPoint(p);
      var p2 = this.g2.body.GetWorldPoint(p);
      var p3 = this.g3.body.GetWorldPoint(p);

      context.strokeStyle = 'grey';
      context.lineWidth = 0.4;
      context.lineCap = 'round';

      context.beginPath();
      context.moveTo(p1.x, p1.y);
      context.quadraticCurveTo(p2.x, p2.y, p3.x, p3.y);
      context.stroke();
  };

    var lastX, grass = [], context = document.getElementById('canvas').getContext('2d');

    function updateGraphics(time) {
      window.requestAnimationFrame(updateGraphics);

      wind = 0.95*wind + 0.05*(POWER_MOUSE_WIND*windInput + POWER_RANDOM_WIND*Math.random() - POWER_RANDOM_WIND/2);
      windInput = 0;
      world.SetGravity(new B2Vec2(wind, -10));

      physicalObjects.forEach(function(obj) { if (obj.update) obj.update(time); });
      world.Step(1/60, 8, 3);
      world.ClearForces();

      context.clearRect(0, 0, context.canvas.width, context.canvas.height);
      context.save();
      context.translate(context.canvas.width/2, context.canvas.height/2);
      context.scale(context.canvas.width/20, -context.canvas.width/20);
      grass.forEach(function (o) { o.draw(context); });
      context.restore();
    }

    document.getElementsByTagName('body')[0].addEventListener("mousemove", function (e) {
      windInput = Math.abs(lastX - e.x) < 200? 0.2*(e.x - lastX) : 0;
      lastX = e.x;
    });

    var W = 8;
    for (var i = 0; i < STRAW_COUNT; i++) {
      grass.push(new Grass(new B2Vec2(W*(i/(STRAW_COUNT-1))-W/2, -1)));
    }

    window.requestAnimationFrame(updateGraphics);
})();

回答2:

Waving grass algorithm

UPDATE

I made a reduced update to better meet what I believe is your requirements. To use mouse you just calculate the angle between the mouse point and the strain root and use that for new angle in the update.

I have incorporated a simple mouse-move sensitive approach which makes the strains "point" towards the mouse, but you can add random angles to this as deltas and so forth. Everything you need is as said in the code - adjust as needed.

New fiddle (based on previous with a few modifications):
http://jsfiddle.net/AbdiasSoftware/yEwGc/

Image showing 150 strains being simulated.

Grass simulation demo:
http://jsfiddle.net/AbdiasSoftware/5z89V/

This will generate a nice realistic looking grass field. The demo has 70 grass rendered (works best in Chrome or just lower the number for Firefox).

The code is rather simple. It consists of a main object (grassObj) which contains its geometry as well as functions to calculate the angles, segments, movements and so forth. I'll show this in detail below.

First some inits that are accessed globally by the functions:

var numOfGrass = 70,  /// number of grass strains
    grass,

    /// get canvas context
    ctx = canvas.getContext('2d'),
    w = canvas.width,
    h = canvas.height,

    /// we use an animated image for the background
    /// The image also clears the canvas for each loop call
    /// I rendered the clouds in a 3D software.
    img = document.createElement('img'),
    ix = 0,  /// background image position
    iw = -1; /// used for with and initial for flag

    /// load background image, use it whenever it's ready
    img.onload = function() {iw = this.width}
    img.src = 'http://i.imgur.com/zzjtzG7.jpg';

The heart - grassObj

The main object as mentioned above is the grassObj:

function grassObj(x, y, seg1, seg2, maxAngle) {

    /// exposed properties we need for rendering
    this.x = x;        /// bottom position of grass
    this.y = y;
    this.seg1 = seg1;  /// segments of grass
    this.seg2 = seg2; 
    this.gradient = getGradient(Math.random() * 50 + 50, 100 * Math.random() + 170);

    this.currentAngle; ///current angle that will be rendered

    /// internals used for calculating new angle, goal, difference and speed
    var counter,       /// counter between 0-1 for ease-in/out
        delta,         /// random steps in the direction goal rel. c.angle.
        angle,         /// current angle, does not change until goal is reached
        diff,          /// diff between goal and angle
        goal = getAngle();

    /// internal: returns an angel between 0 and maxAngle
    function getAngle() {
        return maxAngle * Math.random();
    }

    /// ease in-out function
    function easeInOut(t) {
        return t < 0.5 ? 4 * t * t * t : (t-1) * (2 * t - 2) * (2 * t - 2) + 1;
    }

    /// sets a new goal for grass to move to. Does the main calculations
    function newGoal() {
        angle = goal;        /// set goal as new angle when reached
        this.currentAngle = angle;
        goal = getAngle();   /// get new goal
        diff = goal - angle; /// calc diff
        counter = 0;         /// reset counter

        delta = (4 * Math.random() + 1) / 100;
    }

    /// creates a gradient for this grass to increase realism
    function getGradient(min, max) {

        var g = ctx.createLinearGradient(0, 0, 0, h);
        g.addColorStop(1,   'rgb(0,' + parseInt(min) + ', 0)');
        g.addColorStop(0,   'rgb(0,' + parseInt(max) + ', 0)');

        return g;
    }

    /// this is called from animation loop. Counts and keeps tracks of 
    /// current position and calls new goal when current goal is reached
    this.update = function() {

        /// count from 0 to 1 with random delta value   
        counter += delta;

        /// if counter passes 1 then goal is reached -> get new goal
        if (counter > 1) {
            newGoal();
            return;
        }

        /// ease in/out function
        var t = easeInOut(counter);

        /// update current angle for render
        this.currentAngle = angle + t * diff;
    }

    /// init
    newGoal();

    return this;
}

Grass generator

We call makeGrass to generate grass at random positions, random heights and with random segments. The function is called with number of grass to render, width and height of canvas to fill and a variation variable in percent (0 - 1 float).

The single grass consist only of four points in total. The two middle points are spread about 1/3 and 2/3 of the total height with a little variation to break pattern. The points when rendered, are smoother using a cardinal spline with full tension to make the grass look smooth.

function makeGrass(numOfGrass, width, height, hVariation) {

    /// setup variables
    var x, y, seg1, seg2, angle,
        hf = height * hVariation,  /// get variation
        i = 0,
        grass = [];                /// array to hold the grass

    /// generate grass
    for(; i < numOfGrass; i++) {

        x = width * Math.random();        /// random x position
        y = height - hf * Math.random();  /// random height

        /// break grass into 3 segments with random variation
        seg1 = y / 3 + y * hVariation * Math.random() * 0.1;
        seg2 = (y / 3 * 2) + y * hVariation * Math.random() * 0.1;

        grass.push(new grassObj(x, y, seg1, seg2, 15 * Math.random() + 50));
}

    return grass;
}

Render

The render function just loops through the objects and updates the current geometry:

function renderGrass(ctx, grass) {

    /// local vars for animation
    var len = grass.length,
        i = 0,
        gr, pos, diff, pts, x, y;

    /// renders background when loaded
    if (iw > -1) {
        ctx.drawImage(img, ix--, 0);
        if (ix < -w) {
            ctx.drawImage(img, ix + iw, 0);
        }
        if (ix <= -iw) ix = 0;
    } else {
        ctx.clearRect(0, 0, w, h);
    }

    /// loops through the grass object and renders current state
    for(; gr = grass[i]; i++) {

        x = gr.x;
        y = gr.y;

        ctx.beginPath();

        /// calculates the end-point based on length and angle
        /// Angle is limited [0, 60] which we add 225 deg. to get
        /// it upwards. Alter 225 to make grass lean more to a side.
        pos = lineToAngle(ctx, x, h, y, gr.currentAngle + 225);

        /// diff between end point and root point
        diff = (pos[0] - x)

        pts = [];

        /// starts at bottom, goes to top middle and then back
        /// down with a slight offset to make the grass

        pts.push(x); /// first couple at bottom
        pts.push(h);

        /// first segment 1/4 of the difference
        pts.push(x + (diff / 4));
        pts.push(h - gr.seg1);

        /// second segment 2/3 of the difference
        pts.push(x + (diff / 3 * 2));
        pts.push(h - gr.seg2);

        pts.push(pos[0]);    /// top point
        pts.push(pos[1]);

        /// re-use previous data, but go backward down to root again
        /// with a slight offset
        pts.push(x + (diff / 3 * 2) + 10);
        pts.push(h - gr.seg2);

        pts.push(x + (diff / 4) + 12);
        pts.push(h - gr.seg1 + 10);

        pts.push(x + 15); /// end couple at bottom
        pts.push(h);

        /// smooth points (extended context function, see demo)
        ctx.curve(pts, 0.8, 5);

        ctx.closePath();

        /// fill grass with its gradient
        ctx.fillStyle = gr.gradient;
        ctx.fill();
    }
}

Animate

The main loop where we animate everything:

function animate() {

    /// update each grass objects
    for(var i = 0;i < grass.length; i++) grass[i].update();            

    /// render them
    renderGrass(ctx, grass);

    /// loop
    requestAnimationFrame(animate);
}

And that's all there is to it for this version.

回答3:

Darn! Late to the party...

But LOTS of neat answers here -- I'm upvoting all !

Anyway, here's my idea:

Here's code and a Fiddle: http://jsfiddle.net/m1erickson/MJjHz/

<!doctype html>
<html>
  <head>

    <link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
    <script src="http://code.jquery.com/jquery-1.9.1.js"></script>
    <script src="http://code.jquery.com/ui/1.10.1/jquery-ui.js"></script>

    <style>
      body { font-family: arial; padding:15px; }
      canvas { border: 1px solid red;}
      input[type="text"]{width:35px;}
    </style>

  </head>
  <body>
      <p>Move mouse across hairs</p>
      <canvas height="100" width="250" id="canvas"></canvas>
  <script>

      $(function() {

        var canvas=document.getElementById("canvas");
        var ctx = canvas.getContext("2d");
        var canvasOffset=$("#canvas").offset();
        var offsetX=canvasOffset.left;
        var offsetY=canvasOffset.top;

        var cHeight=canvas.height;
        var showControls=false;
        var lastMouseX=0;

        // preset styling CONSTANTS
        var SWAY=.55;     // max endpoint sway from center 
        var C1Y=.40;      // fixed Y of cp#1
        var C2SWAY=.20    // max cp#2 sway from center
        var C2Y=.75;      // fixed Y of cp#2
        var YY=20;        // max height of ellipse at top of hair
        var PIPERCENT=Math.PI/100;

        var hairs=[];

        // create hairs
        var newHairX=40;
        var hairCount=20;
        for(var i=0;i<hairCount;i++){
            var randomLength=50+parseInt(Math.random()*5);
            addHair(newHairX+(i*8),randomLength);
        }

        function addHair(x,length){
            hairs.push({
                x:x,
                length:length,
                left:0,
                right:0,
                top:0,
                s:{x:0,y:0},
                c1:{x:0,y:0},
                c2:{x:0,y:0},
                e:{x:0,y:0},
                isInMotion:false,
                currentX:0
            });
        }

        for(var i=0;i<hairs.length;i++){
            var h=hairs[i];
            setHairPointsFixed(h);
            setHairPointsPct(h,50);
            draw(h);
        }

        function setHairPointsFixed(h){
            h.s.x   = h.x;
            h.s.y   = cHeight;
            h.c1.x  = h.x;
            h.c1.y  = cHeight-h.length*C1Y;
            h.c2.y  = cHeight-h.length*C2Y;
            h.top   = cHeight-h.length;
            h.left  = h.x-h.length*SWAY;
            h.right = h.x+h.length*SWAY;
        }


        function setHairPointsPct(h,pct){
            // endpoint
            var a=Math.PI+PIPERCENT*pct;
            h.e.x  = h.x - ((h.length*SWAY)*Math.cos(a));
            h.e.y  = h.top + (YY*Math.sin(a));
            // controlpoint#2
            h.c2.x = h.x + h.length*(C2SWAY*2*pct/100-C2SWAY);
        }

        //////////////////////////////

        function handleMouseMove(e){
          mouseX=parseInt(e.clientX-offsetX);
          mouseY=parseInt(e.clientY-offsetY);

          // draw this frame based on mouse moves
          ctx.clearRect(0,0,canvas.width,canvas.height);
          for(var i=0;i<hairs.length;i++){
              hairMoves(hairs[i],mouseX,mouseY);
          }

          lastMouseX=mouseX;
        }
        $("#canvas").mousemove(function(e){handleMouseMove(e);});



        function hairMoves(h,mouseX,mouseY){

          // No hair movement if not touching hair
          if(mouseY<cHeight-h.length-YY){
              if(h.isInMotion){
                  h.isInMotion=false;
                  setHairPointsPct(h,50);
              }
              draw(h);
              return;
          }

          // No hair movement if too deep in hair
          if(mouseY>h.c1.y){
              draw(h);
              return;
          }

          //
          var pct=50;
          if(mouseX>=h.left && mouseX<=h.right){

              if(h.isInMotion){

                  var pct=-(mouseX-h.right)/(h.right-h.left)*100;
                  setHairPointsPct(h,pct);
                  draw(h);

              }else{

                  // if hair is at rest 
                  // but mouse has just contacted hair
                  // set hair in motion
                  if(   (lastMouseX<=h.x && mouseX>=h.x )
                      ||(lastMouseX>=h.x && mouseX<=h.x )
                  ){
                      h.isInMotion=true;
                      var pct=-(mouseX-h.right)/(h.right-h.left)*100;
                  }
                  setHairPointsPct(h,pct);
                  draw(h);

              }

          }else{
              if(h.isInMotion){
                  h.isInMotion=false;
                  setHairPointsPct(h,50);
              };
              draw(h);
          }

        }


        function dot(pt,color){
            ctx.beginPath();
            ctx.arc(pt.x,pt.y,5,0,Math.PI*2,false);
            ctx.closePath();
            ctx.fillStyle=color;
            ctx.fill();
        }


        function draw(h){

            ctx.beginPath();
            ctx.moveTo(h.s.x,h.s.y);
            ctx.bezierCurveTo(h.c1.x,h.c1.y,h.c2.x,h.c2.y,h.e.x,h.e.y);
            ctx.strokeStyle="orange";
            ctx.lineWidth=3;
            ctx.stroke();

            if(showControls){
                dot(h.s,"green");
                dot(h.c1,"red");
                dot(h.c2,"blue");
                dot(h.e,"purple");

                ctx.beginPath();
                ctx.rect(h.left,h.top-YY,(h.right-h.left),h.length*(1-C1Y)+YY)
                ctx.lineWidth=1;
                ctx.strokeStyle="lightgray";
                ctx.stroke();
            }

        }


    });
    </script>

  </body>   
</html>

回答4:

Here is a simple hair simulation that seems to be what you are looking for. The basic idea is to draw a bezier curve (in this case I use two curves to provide thickness for the hair). The curve will have a base, a bending point, and a tip. I set the bending point halfway up the hair. The tip of the hair will rotate about the axis of the base of the hair in response to mouse movement.

Place this code in a script tag below the canvas element declaration.

    function Point(x, y) {
        this.x = x;
        this.y = y;
    }

    function Hair( )  {
        this.height = 100;   // hair height
        this.baseWidth = 3;    // hair base width.
        this.thickness = 1.5; // hair thickness
        this.points = {};

        this.points.base1 = new Point(Math.random()*canvas.width, canvas.height);

        // The point at which the hair will bend. I set it to the middle of the hair, but you can adjust this.
        this.points.bendPoint1 = new Point(this.points.base1.x-this.thickness, this.points.base1.y - this.height / 2)

        this.points.bendPoint2 = new Point(this.points.bendPoint1.x, this.points.bendPoint1.y-this.thickness); // complement of bendPoint1 - we use this because the hair has thickness
        this.points.base2 = new Point(this.points.base1.x + this.baseWidth, this.points.base1.y) // complement of base1 - we use this because the hair has thickness
    }

    Hair.prototype.paint = function(mouseX, mouseY, direction) {    
        ctx.save();

        // rotate the the tip of the hair
        var tipRotationAngle = Math.atan(Math.abs(this.points.base1.y - mouseY)/Math.abs(this.points.base1.x - mouseX));

        // if the mouse is on the other side of the hair, adjust the angle
        if (mouseX < this.points.base1.x) {
            tipRotationAngle = Math.PI - tipRotationAngle;
        }

        // if the mouse isn't close enough to the hair, it shouldn't affect the hair
        if (mouseX < this.points.base1.x - this.height/2 || mouseX > this.points.base1.x + this.height/2 || mouseY < this.points.base1.y - this.height || mouseY > this.points.base1.y) {
            tipRotationAngle = Math.PI/2; // 90 degrees, which means the hair is straight
        }

        // Use the direction of the mouse to as a lazy way to simulate the direction the hair should bend.
        // Note that in real life, the direction that the hair should bend has nothing to do with the direction of motion. It actually depends on which side of the hair the force is being applied.
        // Figuring out which side of the hair the force is being applied is a little tricky, so I took this shortcut.
        // If you run your finger along a comb quickly, this approximation will work. However if you are in the middle of the comb and slowly change direction, you will notice that the force is still applied in the opposite direction of motion as you slowly back off the set of tines.
        if ((mouseX < this.points.base1.x && direction == 'right') || (mouseX > this.points.base1.x && direction == 'left')) {
            tipRotationAngle = Math.PI/2; // 90 degrees, which means the hair is straight
        }

        var tipPoint = new Point(this.points.base1.x + this.baseWidth + this.height*Math.cos(tipRotationAngle), this.points.base1.y - this.height*Math.sin(tipRotationAngle));

        ctx.beginPath();
        ctx.moveTo(this.points.base1.x, this.points.base1.y); // start at the base
        ctx.bezierCurveTo(this.points.base1.x, this.points.base1.y, this.points.bendPoint1.x, this.points.bendPoint1.y, tipPoint.x, tipPoint.y); // draw a curve to the tip of the hair
        ctx.bezierCurveTo(tipPoint.x, tipPoint.y, this.points.bendPoint2.x, this.points.bendPoint2.y, this.points.base2.x, this.points.base2.y); // draw a curve back down to the base using the complement points since the hair has thickness.
        ctx.closePath(); // complete the path so we have a shape that we can fill with color
        ctx.fillStyle='rgb(0,0,0)';
        ctx.fill();

        ctx.restore();
    }  

    // I used global variables to keep the example simple, but it is generally best to avoid using global variables
    window.canvas = document.getElementById('myCanvas');
    window.ctx = canvas.getContext('2d');
    ctx.fillStyle = 'rgb(200,255,255)'; // background color
    window.hair = [];
    window.prevClientX = 0;

    for (var i = 0; i < 100; i++) {
        hair.push(new Hair());
    }

    // initial draw
    ctx.fillRect(0,0,canvas.width,canvas.height); // clear canvas
    for (var i = 0; i < hair.length; i++) {
        hair[i].paint(0, 0, 'right');
    }

    window.onmousemove = function(e)    {
        ctx.fillRect(0,0,canvas.width,canvas.height); // clear canvas

        for (var i = 0; i < hair.length; i++) {
            hair[i].paint(e.clientX, e.clientY, e.clientX > window.prevClientX ? 'right' : 'left');
        }
        window.prevClientX = e.clientX;
    }

回答5:

Made this some time ago, might be useful to some people. Just adjust the variables at the beginning of the code with the values that fits your wishes:

...
Mheight = 1;
height = 33;
width = 17;
distance = 10;
randomness = 14;
angle = Math.PI / 2;
...

Also on http://lucasm0ta.github.io/JsGrass/