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Fill an Unknown Asymmetric Polygon with Pixel Manipulation (WebImage) in JS

Recently, I have been trying to create code to fill a polygon of any shape with color. I have gotten as far as being able to fill a shape that has lines of only one border size correctly, though I have found myself unable to do anything more than that. The problem is that the code does not know when to consider a line of pixels greater than that which it expects as a vertical or horizontal border of the shape. I am going through each pixel of the shape from left to right and checking if any of the pixels have any form of color by checking if the alpha value is 0 or not. Once it finds a pixel that does have an alpha value of anything other than 0, it moves forward a single pixel and then uses the even/odd technique to determine whether the point is inside part of the polygon or not (it makes an infinite line to the right and determines if the number of collisions with colored lines is odd, and if it is, the point is inside the polygon). In general, we consider a single, lone pixel to count as a single line, and we consider a horizontal line of more than one pixel to be two lines because of how often horizontal lines will be part of a border or not. Take the following scenario:
Here, the red dot is the point (pixel) we begin testing from. If we did not consider that horizontal line in the middle to be two points (as is shown by the red lines and x's), we would only have two points of intersection and therefore would not fill the pixel despite the fact that we most definitely do want to fill that pixel. As stated earlier, however, this brings up another problem with a different scenario:
In this case, if we do count a horizontal line of more than one pixel to be two separate lines, we end up not filling any areas with borders that are thicker than the expected thickness. For your reference, the function to handle this is as follows:
//imgData is essentially a WebImage object (explained more below) and r, g, and b are the color values for the fill color
function fillWithColor(imgData, r, g, b) {
//Boolean determining whether we should color the given pixel(s) or not
var doColor = false;
//Booleans determining whether the last pixel found in the entire image was colored
var blackLast = false;
//Booleans determining whether the last 1 or 2 pixels found after a given pixel were colored
var foundBlackPrev, foundBlackPrev2 = false;
//The number of colored pixels found
var blackCount = 0;
//Loop through the entire canvas
for(var y = 0; y < imgData.height; y += IMG_SCALE) {
for(var x = 0; x < imgData.width; x += IMG_SCALE) {
//Test if given pixel is colored
if(getAlpha(imgData, x, y) != 0) {
//If the last pixel was black, begin coloring
if(!blackLast) {
blackLast = true;
doColor = true;
}
} else {
//If the current pixel is not colored, but the last one was, find all colored lines to the right
if(blackLast){
for(var i = x; i < imgData.width; i += IMG_SCALE) {
//If the pixel is colored...
if(getAlpha(imgData, i, y) != 0) {
//If no colored pixel was found before, add to the count
if(!foundBlackPrev){
blackCount++;
foundBlackPrev = true;
} else {
//Otherwise, at least 2 colored pixels have been found in a row
foundBlackPrev2 = true;
}
} else {
//If two or more colored pixels were found in a row, add to the count
if(foundBlackPrev2) {
blackCount++;
}
//Reset the booleans
foundBlackPrev2 = foundBlackPrev = false;
}
}
}
//If the count is odd, we start coloring
if(blackCount & 1) {
blackCount = 0;
doColor = true;
} else {
//If the last pixel in the entire image was black, we stop coloring
if(blackLast) {
doColor = false;
}
}
//Reset the boolean
blackLast = false;
//If we are to be coloring the pixel, color it
if(doColor) {
//Color the pixel
for(var j = 0; j < IMG_SCALE; j++) {
for(var k = 0; k < IMG_SCALE; k++) {
//This is the same as calling setRed, setGreen, setBlue and setAlpha functions from the WebImage API all at once (parameters in order are WebImage object equivalent, x position of pixel, y position of pixel, red value, green value, blue value, and alpha value)
setRGB(imgData, x + j, y + k, r, g, b, 255);
}
}
}
}
}
}
//Update the image (essentially the same as removing all elements from the given area and calling add on the image)
clearCanvas();
putImageData(imgData, 0, 0, imgData.width, imgData.height);
//Return the modified data
return imgData;
}
Where...
imgData is the collection of all of the pixels in the given area (essentially a WebImage object)
IMG_SCALE is the integer value by which the image has been scaled up (which gives us the scale of the pixels as well). In this example, it is equal to 4 because the image is scaled up to 192x256 (from 48x64). This means that every "pixel" you see in the image is actually comprised of a 4x4 block of identically-colored pixels.
So, what I'm really looking for here is a way to determine whether a given colored pixel that comes after another is part of a horizontal border or if it is just another piece comprising the thickness of a vertical border. In addition, if I have the wrong approach to this problem in general, I would greatly appreciate any suggestions as to how to do this more efficiently. Thank you.

I understand the problem and I think you would do better if you would switch your strategy here. We know the following:
the point of start is inside the shape
the color should be filled for every pixel inside the shape
So, we could always push the neighbors of the current point into a queue to be processed and be careful to avoid processing the same points twice, this way traversing all the useful pixels and including them into the coloring plan. The function below is untested.
function fillColor(pattern, startingPoint, color, boundaryColor) {
let visitQueue = [];
let output = {};
if (startingPoint.x - 1 >= 0) visitQueue.push({startingPoint.x - 1, startingPoint.y});
if (startingPoint.x + 1 < pattern.width) visitQueue.push({startingPoint.x + 1, startingPoint.y});
if (startingPoint.y + 1 < pattern.height) visitQueue.push({startingPoint.x, startingPoint.y + 1});
if (startingPoint.y - 1 >= 0) visitQueue.push({startingPoint.x, startingPoint.y - 1});
let visited = {};
while (visitQueue.length > 0) {
let point = visitQueue[0];
visitQueue.shift();
if ((!visited[point.x]) || (visited[point.x].indexOf(point.y) < 0)) {
if (!visited[point.x]) visited[point.x] = [];
visited[point.x].push(point.y);
if (isBlank(pattern, point)) { //you need to implement isBlank
if (!output[point.x]) output[point.x] = [];
output[point.x].push(point.y);
if (point.x + 1 < pattern.width) visitQueue.push({point.x + 1, point.y});
if (point.x - 1 >= 0) visitQueue.push({point.x - 1, point.y});
if (point.y + 1 < pattern.height) visitQueue.push({point.x, point.y + 1});
if (point.y - 1 >= 0) visitQueue.push({point.x, point.y - 1})
}
}
}
return output;
}

As far as I understood you cannot "consider a horizontal line of more than one pixel to be two lines". I don't think you need to count black pixels the way you do, rather count groups of 1 or more pixels.
I would also tidy the code by avoiding using the "doColor" boolean variable. You could rather move the coloring code to a new function color(x,y) and call it straight away.

const ctx = document.querySelector("canvas").getContext("2d");
//ctx.lineWidth(10);//-as you asked we are setting greater border or line width,BUT "LINEWIDTH" IS NOT WORKING IN INBUILT STACKOVERFLOW SNIPPET USE IT IN A FILE I THINK STACKOVERFLOW IS NOT UP-TO-DATE,IN ANY IDE UNCOMENT THIS
ctx.beginPath();
ctx.moveTo(20, 20);
ctx.lineTo(250, 70);
ctx.lineTo(270, 120);
ctx.lineTo(170, 140);
ctx.lineTo(190, 80);
ctx.lineTo(100, 60);
ctx.lineTo(50, 130);
ctx.lineTo(20, 20);
ctx.stroke();
function getMousePosition(canvas, event) {
let rect = canvas.getBoundingClientRect();
let mx = event.clientX - rect.left;
let my = event.clientY - rect.top;
console.log("Coordinate x: " + mx, "Coordinate y: " + my);
floodFill(ctx, mx, my, [155, 0, 255, 255], 128);
}
let canvasElem = document.querySelector("canvas");
canvasElem.addEventListener("mousedown", function(e) {
getMousePosition(canvasElem, e);
});
function getPixel(imageData, x, y) {
if (x < 0 || y < 0 || x >= imageData.width || y >= imageData.height) {
return [-1, -1, -1, -1]; // impossible color
} else {
const offset = (y * imageData.width + x) * 4;
return imageData.data.slice(offset, offset + 4);
}
}
function setPixel(imageData, x, y, color) {
const offset = (y * imageData.width + x) * 4;
imageData.data[offset + 0] = color[0];
imageData.data[offset + 1] = color[1];
imageData.data[offset + 2] = color[2];
imageData.data[offset + 3] = color[0];
}
function colorsMatch(a, b, rangeSq) {
const dr = a[0] - b[0];
const dg = a[1] - b[1];
const db = a[2] - b[2];
const da = a[3] - b[3];
return dr * dr + dg * dg + db * db + da * da < rangeSq;
}
function floodFill(ctx, x, y, fillColor, range = 1) {
// read the pixels in the canvas
const imageData = ctx.getImageData(0, 0, ctx.canvas.width, ctx.canvas.height);
// flags for if we visited a pixel already
const visited = new Uint8Array(imageData.width, imageData.height);
// get the color we're filling
const targetColor = getPixel(imageData, x, y);
// check we are actually filling a different color
if (!colorsMatch(targetColor, fillColor)) {
const rangeSq = range * range;
const pixelsToCheck = [x, y];
while (pixelsToCheck.length > 0) {
const y = pixelsToCheck.pop();
const x = pixelsToCheck.pop();
const currentColor = getPixel(imageData, x, y);
if (!visited[y * imageData.width + x] &&
colorsMatch(currentColor, targetColor, rangeSq)) {
setPixel(imageData, x, y, fillColor);
visited[y * imageData.width + x] = 1; // mark we were here already
pixelsToCheck.push(x + 1, y);
pixelsToCheck.push(x - 1, y);
pixelsToCheck.push(x, y + 1);
pixelsToCheck.push(x, y - 1);
}
}
// put the data back
ctx.putImageData(imageData, 0, 0);
}
}
<canvas></canvas>
This is based on other answers
note:"LINEWIDTH" IS NOT WORKING IN INBUILT STACKOVERFLOW SNIPPET USE IT IN A FILE I THINK STACKOVERFLOW IS NOT UP-TO-DATE,
But it works well in simple HTML,JS website

JavaScript Canvas how to stroke special text [duplicate]

I'm drawing an image onto a canvas using drawImage. It's a PNG that is surrounded by transparent pixels, like this:
How can I add a solid-colored border to the visible part of that image on the canvas? To clarify: I don't want a rectangle that surrounds the image's bounding box. The border should go around the grass patch.
I did consider using shadows, but I don't really want a glowing border, I want a solid one.

A bit late, but just draw the image offset which is much faster than analyzing the edges:
var ctx = canvas.getContext('2d'),
img = new Image;
img.onload = draw;
img.src = "http://i.stack.imgur.com/UFBxY.png";
function draw() {
var dArr = [-1,-1, 0,-1, 1,-1, -1,0, 1,0, -1,1, 0,1, 1,1], // offset array
s = 2, // thickness scale
i = 0, // iterator
x = 5, // final position
y = 5;
// draw images at offsets from the array scaled by s
for(; i < dArr.length; i += 2)
ctx.drawImage(img, x + dArr[i]*s, y + dArr[i+1]*s);
// fill with color
ctx.globalCompositeOperation = "source-in";
ctx.fillStyle = "red";
ctx.fillRect(0,0,canvas.width, canvas.height);
// draw original image in normal mode
ctx.globalCompositeOperation = "source-over";
ctx.drawImage(img, x, y);
}
<canvas id=canvas width=500 height=500></canvas>

==> ==>
First, attributions:
As #Philipp says, you'll need to analyze pixel data to get your outline border.
You can use the "Marching Squares" algorithm to determine which transparent pixels border the non-transparent grass pixels. You can read more about the Marching Squares algorithm here: http://en.wikipedia.org/wiki/Marching_squares
Michael Bostock has a very nice plugin version of Marching Squares in his d3 data visualization application (IMHO, d3 is the best open-source data visualization program available). Here's a link to the plugin: https://github.com/d3/d3-plugins/tree/master/geom/contour
You can outline the border of your grass image like this:
Draw your image on the canvas
Grab the image's pixel data using .getImageData
Configure the plug-in to look for transparent pixels bordering opaque pixels
// This is used by the marching ants algorithm
// to determine the outline of the non-transparent
// pixels on the image using pixel data
var defineNonTransparent=function(x,y){
var a=data[(y*cw+x)*4+3];
return(a>20);
}
Call the plugin which returns a set of points which outline the border of your image.
// call the marching ants algorithm
// to get the outline path of the image
// (outline=outside path of transparent pixels
points=geom.contour(defineNonTransparent);
Use the set of points to draw a path around your image.
Here's annotated code and a Demo:
// Marching Squares Edge Detection
// this is a "marching ants" algorithm used to calc the outline path
(function() {
// d3-plugin for calculating outline paths
// License: https://github.com/d3/d3-plugins/blob/master/LICENSE
//
// Copyright (c) 2012-2014, Michael Bostock
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//* Redistributions of source code must retain the above copyright notice, this
// list of conditions and the following disclaimer.
//* Redistributions in binary form must reproduce the above copyright notice,
// this list of conditions and the following disclaimer in the documentation
// and/or other materials provided with the distribution.
//* The name Michael Bostock may not be used to endorse or promote products
// derived from this software without specific prior written permission.
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL MICHAEL BOSTOCK BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
geom = {};
geom.contour = function(grid, start) {
var s = start || d3_geom_contourStart(grid), // starting point
c = [], // contour polygon
x = s[0], // current x position
y = s[1], // current y position
dx = 0, // next x direction
dy = 0, // next y direction
pdx = NaN, // previous x direction
pdy = NaN, // previous y direction
i = 0;
do {
// determine marching squares index
i = 0;
if (grid(x-1, y-1)) i += 1;
if (grid(x, y-1)) i += 2;
if (grid(x-1, y )) i += 4;
if (grid(x, y )) i += 8;
// determine next direction
if (i === 6) {
dx = pdy === -1 ? -1 : 1;
dy = 0;
} else if (i === 9) {
dx = 0;
dy = pdx === 1 ? -1 : 1;
} else {
dx = d3_geom_contourDx[i];
dy = d3_geom_contourDy[i];
}
// update contour polygon
if (dx != pdx && dy != pdy) {
c.push([x, y]);
pdx = dx;
pdy = dy;
}
x += dx;
y += dy;
} while (s[0] != x || s[1] != y);
return c;
};
// lookup tables for marching directions
var d3_geom_contourDx = [1, 0, 1, 1,-1, 0,-1, 1,0, 0,0,0,-1, 0,-1,NaN],
d3_geom_contourDy = [0,-1, 0, 0, 0,-1, 0, 0,1,-1,1,1, 0,-1, 0,NaN];
function d3_geom_contourStart(grid) {
var x = 0,
y = 0;
// search for a starting point; begin at origin
// and proceed along outward-expanding diagonals
while (true) {
if (grid(x,y)) {
return [x,y];
}
if (x === 0) {
x = y + 1;
y = 0;
} else {
x = x - 1;
y = y + 1;
}
}
}
})();
//////////////////////////////////////////
// canvas related variables
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
// checkbox to show/hide the original image
var $showImage=$("#showImage");
$showImage.prop('checked', true);
// checkbox to show/hide the path outline
var $showOutline=$("#showOutline");
$showOutline.prop('checked', true);
// an array of points that defines the outline path
var points;
// pixel data of this image for the defineNonTransparent
// function to use
var imgData,data;
// This is used by the marching ants algorithm
// to determine the outline of the non-transparent
// pixels on the image
var defineNonTransparent=function(x,y){
var a=data[(y*cw+x)*4+3];
return(a>20);
}
// load the image
var img=new Image();
img.crossOrigin="anonymous";
img.onload=function(){
// draw the image
// (this time to grab the image's pixel data
ctx.drawImage(img,canvas.width/2-img.width/2,canvas.height/2-img.height/2);
// grab the image's pixel data
imgData=ctx.getImageData(0,0,canvas.width,canvas.height);
data=imgData.data;
// call the marching ants algorithm
// to get the outline path of the image
// (outline=outside path of transparent pixels
points=geom.contour(defineNonTransparent);
ctx.strokeStyle="red";
ctx.lineWidth=2;
$showImage.change(function(){ redraw(); });
$showOutline.change(function(){ redraw(); });
redraw();
}
img.src="http://i.imgur.com/QcxIJxa.png";
// redraw the canvas
// user determines if original-image or outline path or both are visible
function redraw(){
// clear the canvas
ctx.clearRect(0,0,canvas.width,canvas.height);
// draw the image
if($showImage.is(':checked')){
ctx.drawImage(img,canvas.width/2-img.width/2,canvas.height/2-img.height/2);
}
// draw the path (consisting of connected points)
if($showOutline.is(':checked')){
// draw outline path
ctx.beginPath();
ctx.moveTo(points[0][0],points[0][4]);
for(var i=1;i<points.length;i++){
var point=points[i];
ctx.lineTo(point[0],point[1]);
}
ctx.closePath();
ctx.stroke();
}
}
body{ background-color: ivory; }
canvas{border:1px solid red;}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<input type="checkbox" id="showImage" />Show Image<br>
<input type="checkbox" id="showOutline" />Show Outline Path<br>
<canvas id="canvas" width=300 height=450></canvas>

I was looking for a way to do this and it seems there are only laborious solutions.
I came up with a little workaround using shadows and a loop to display them all around the image:
// Shadow color and blur
// To get a blurry effect use rgba() with a low opacity as it will be overlaid
context.shadowColor = "red";
context.shadowBlur = 0;
// X offset loop
for(var x = -2; x <= 2; x++){
// Y offset loop
for(var y = -2; y <= 2; y++){
// Set shadow offset
context.shadowOffsetX = x;
context.shadowOffsetY = y;
// Draw image with shadow
context.drawImage(img, left, top, width, height);
}
}

Extract wave data from wave form image using HTML5 canvas

I've seen people try to extract the data from a wave form image using php but can this or has anyone ver achieved it using HTML5 canvas?

You could use the ImageData to examine each row, column or pixel. You'll need to use:
var ctx = canvas.getContext("2d");
var imageData = ctx.getImageData(0, 0, canvas.width, canvas.height)
The image data is an array of r, g, b, and a pixel values so the first pixel on the canvas is at indices 0(r), 1(g), 2(b) and 3(a).

You can use the Marching Squares algorithm to fetch a set of points along the image representing the wave.
The excellent d3 library has a plug-in that implements Marching Squares.
The plugin can be used separately outside d3 to get your wave contour point set.
The plugin code is liberally licensed (see copyright notice below).
(function() {
d3.geom.contour = function(grid, start) {
var s = start || d3_geom_contourStart(grid), // starting point
c = [], // contour polygon
x = s[0], // current x position
y = s[1], // current y position
dx = 0, // next x direction
dy = 0, // next y direction
pdx = NaN, // previous x direction
pdy = NaN, // previous y direction
i = 0;
do {
// determine marching squares index
i = 0;
if (grid(x-1, y-1)) i += 1;
if (grid(x, y-1)) i += 2;
if (grid(x-1, y )) i += 4;
if (grid(x, y )) i += 8;
// determine next direction
if (i === 6) {
dx = pdy === -1 ? -1 : 1;
dy = 0;
} else if (i === 9) {
dx = 0;
dy = pdx === 1 ? -1 : 1;
} else {
dx = d3_geom_contourDx[i];
dy = d3_geom_contourDy[i];
}
// update contour polygon
if (dx != pdx && dy != pdy) {
c.push([x, y]);
pdx = dx;
pdy = dy;
}
x += dx;
y += dy;
} while (s[0] != x || s[1] != y);
return c;
};
// lookup tables for marching directions
var d3_geom_contourDx = [1, 0, 1, 1,-1, 0,-1, 1,0, 0,0,0,-1, 0,-1,NaN],
d3_geom_contourDy = [0,-1, 0, 0, 0,-1, 0, 0,1,-1,1,1, 0,-1, 0,NaN];
function d3_geom_contourStart(grid) {
var x = 0,
y = 0;
// search for a starting point; begin at origin
// and proceed along outward-expanding diagonals
while (true) {
if (grid(x,y)) {
return [x,y];
}
if (x === 0) {
x = y + 1;
y = 0;
} else {
x = x - 1;
y = y + 1;
}
}
}
})();
Copyright (c) 2012-2014, Michael Bostock All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
The name Michael Bostock may not be used to endorse or promote products derived from this software without specific prior written
permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL MICHAEL BOSTOCK
BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Grass like smoothing animation on beziercurve?

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"
}

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);
})();

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.

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>

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;
}

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/

Recognize a red ball's position in an image with JavaScript?

Say I have this image:
I'd like to recognize the position of the red ball in the image, I could measure the size of the ball(in pixel) in ahead.
I know that I could draw the image to a canvas, then I could get the pixel color data with context.getImageData, but then what should I do? which algorithm sould I use? I'm new to image processing, thanks a lot.

Here's code dedicated to getting that ball position. The output position will logged to the console so have your JS console open! This code has some values in it that you can play with. I chose some that work for your image such as the rough diameter of the ball being 14 pixels and the threshold for each colour component.
I saved the image as "test.jpg" but you can change the code to the correct image path on line 11.
<!DOCTYPE html>
<html>
<body>
<canvas width="800" height="600" id="testCanvas"></canvas>
<script type="text/javascript">
var img = document.createElement('img');
img.onload = function () {
console.log(getBallPosition(this));
};
img.src = 'test.jpg';
function getBallPosition(img) {
var canvas = document.getElementById('testCanvas'),
ctx = canvas.getContext('2d'),
imageData,
width = img.width,
height = img.height,
pixelData,
pixelRedValue,
pixelGreenValue,
pixelBlueValue,
pixelAlphaValue,
pixelIndex,
redThreshold = 128,
greenThreshold = 40,
blueThreshold = 40,
alphaThreshold = 180,
circleDiameter = 14,
x, y,
count,
ballPosition,
closestBallCount = 0,
closestBallPosition;
// Draw the image to the canvas
canvas.width = width;
canvas.height = height;
ctx.drawImage(img, 0, 0);
// Get the image data
imageData = ctx.getImageData(0, 0, width, height);
pixelData = imageData.data;
// Find the ball!
for (y = 0; y < height; y++) {
// Reset the pixel count
count = 0;
// Loop through the pixels on this line
for (x = 0; x < width; x++) {
// Set the pixel data starting point
pixelIndex = (y * width * 4) + (x * 4);
// Grab the red pixel value
pixelRedValue = pixelData[pixelIndex];
pixelGreenValue = pixelData[pixelIndex + 1];
pixelBlueValue = pixelData[pixelIndex + 2];
pixelAlphaValue = pixelData[pixelIndex + 3];
// Check if the value is within out red colour threshold
if (pixelRedValue >= redThreshold && pixelGreenValue <= greenThreshold && pixelBlueValue <= blueThreshold && pixelAlphaValue >= alphaThreshold) {
count++;
} else {
// We've found a pixel that isn't part of the red ball
// so now check if we found any red data
if (count === circleDiameter) {
// We've found our ball
return {
x: x - Math.floor(circleDiameter / 2),
y: y
};
} else {
// Any data we found was not our ball
if (count < circleDiameter && count > closestBallCount) {
closestBallCount = count;
closestBallPosition = {
x: x - Math.floor(circleDiameter / 2),
y: y
};
}
count = 0;
}
}
}
}
return closestBallPosition;
}
</script>
</body>
</html>

Well i would go and cluster pixels of that color. For example, you could have a look up table where you store red (or in the range of a treshold) pixels (coordinates being the look up key) and an integer value being the cluster id whenever you encounter a pixel without any known red neighbours it starts a new cluster, all other red pixels get the cluster id of a red pixel they are the neighbour of. Depending of you algorithms kernel:
A) XXX B) X
XOX XOX
XXX X
you might need to deal (case B) with a pixel connecting two prior not connected clusters. You would have to replace the cluster id of one of that clusters.
After that you have clusters of pixels. These you can analyse. In case of a round shape i would look for the median in x and y for each cluster and check if all the pixels of that cluster are in the radius.
This will fail if the red ball (or part of it) is in front of another red object. You would than need more complex algorithms.