I have a canvas with width = 900, height = 574. I have all the pixels of the canvas. Inside the canvas there are some rectangles, knowing all the pixels of a rectangle what I want is to find the coordinates of the 4 points of a rectangle and then find the width and height of the rectangle.
So what I did is:
pMinX = (_.min(points)/ 4) % highlightCanvas.width
pMinY = Math.floor((_.min(points) / 4) / highlightCanvas.width)
pMaxX = (_.max(points) / 4) % highlightCanvas.width
pMaxY = Math.floor((_.max(points) / 4) / highlightCanvas.width)
Points is the array of the pixels (4 channels rgba) of the rectangle of which the coordinates I want to find.
pMinY and pMaxY seem to work well while pMinX, pMaX sometimes seem correct while others are wrong.
To test, I created a floating div and resize it according to:
{
width: pMaxX - pMinX
height: pMaxY - pMinY
}
The height of the div is always correct. But the width there are cases that fails.
Any idea why sometimes the calculation fails?
Here's annotated code showing how to calculate the bounding box (x, y, width, height) of the salmon colored rectangle in your image.
It works like this:
Get the r,g,b,a values for each pixel on the canvas using .getImageData.
Set up test(s) that a pixel's rgba must meet to be considered as "inside the desired rectangle" In your example, the salmon rectangle is made up of 2 colors so this test will capture all pixels inside your rectangle:
// create an array to hold tests that are used to
// find your desired pixels. The tests should be functions
// that return true for your desired rgba pixel values
// (substitue whatever algorithm test that are necessary for your design)
var tests=[];
// add a test into the tests[] array
tests.push(function(r,g,b,a){
return(
(r==251 && g==115 && b==119)||
(r==249 && g==100 && b==107)
);
});
Determine the minX, minY, maxX & maxY of pixels meeting the tests
Calculate the bounding box of the rectangle pixels from the determined minimums and maximums:
var bounds={
x:minX,
y:minY,
width:maxX-minX,
height:maxY-minY
};
Important Note: For .getImageData to be allowed, you must satisfy security restrictions. The usual way is to serve the image on the same domain as your webpage. Alternatively, you can set up the server hosting the image to serve that image to any anonymous requestor.
Example code and a Demo:
// canvas related variables
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
// load the image
var img=new Image();
// the image must satisfy cross-origin restrictions
// or else we can't use .getImageData
img.crossOrigin='anonymous';
img.onload=start;
img.src="https://dl.dropboxusercontent.com/u/139992952/multple/findRect.png";
function start(){
// resize the canvas to the image size
// and draw the image onto the canvas
cw=canvas.width=img.width;
ch=canvas.height=img.height;
ctx.drawImage(img,0,0);
// create an array to hold tests that are used to
// find your desired pixels. The tests should be functions
// that return true for your desired rgba pixel values
// (substitue whatever algorithm test that are necessary for
// your design)
var tests=[];
// sample test returns true if matching the 2 colors making up the rect
tests.push(function(r,g,b,a){
return(
(r==251 && g==115 && b==119)||
(r==249 && g==100 && b==107)
);
});
// find the bounds of all pixels meeting the prescribed test(s)
var bounds=findImageBounds(tests);
// testing...draw just the discovered rect to a second canvas
var c=document.createElement('canvas');
var cctx=c.getContext('2d');
document.body.appendChild(c);
c.width=cw;
c.height=ch;
cctx.drawImage(canvas,
bounds.x,bounds.y,bounds.w,bounds.h,
bounds.x,bounds.y,bounds.w,bounds.h
);
}
function findImageBounds(tests){
// get the rgba color values for all pixels on the canvas
var d=ctx.getImageData(0,0,cw,ch).data;
// iterate over each pixel
// find the min/max X,Y of pixels where all tests are true
var minX=1000000;
var minY=1000000;
var maxX=-1000000;
var maxY=-1000000;
var hits=0;
for(var y=0;y<ch;y++){
for(var x=0;x<cw;x++){
// n==the position in the rgba array for canvas position x,y
n=(y*cw+x)*4;
// the rgba values at this pixel
r=d[n];
g=d[n+1];
b=d[n+2];
a=d[n+3];
// run all tests on this pixel
var testsTrue=true;
for(var i=0;i<tests.length;i++){
testsTrue=testsTrue && tests[i](r,g,b,a);
}
// if this pixel meets all tests
// see if it influences our boundary
if(testsTrue){
hits++;
if(x<minX){minX=x;}
if(y<minY){minY=y;}
if(x>minX){maxX=x;}
if(y>maxY){maxY=y;}
}
}}
// return the x,y,width,height of the bounding box
// of pixels meeting all the supplied tests
return({x:minX,y:minY,w:maxX-minX,h:maxY-minY,pixelCount:hits});
}
body{ background-color: ivory; }
canvas{border:1px solid red;}
<h4>The original canvas</h4>
<canvas id="canvas" width=300 height=300></canvas>
<h4>Just the rect from the canvas</h4>
Related
I'm creating an application to calculate how much solar panels would fit on a specific roof.
Users can input the dimensions of their roof.
We only have on size of solar panels available.
I thought a canvas was the way to go but I don't seem to find the information I need..
Requirements
1) Based on the input of the user the canvas should be resized (currently I have a rectangle inside the canvas changing to this size)
2) User should be able to create (and size) objects to put on the roof (chimney, window,..)
3) Based on the open space left solar panels (rectangles) should be automaticly drawn on the canvas
Dimensions and limitations
1px = 2cm
Spacing to edge of roof and object is 7px (14cm)
Solar panel is 169 cm height and 102 cm width
I've checked out the fabric.js library but can't seem to find something close to what I need.
The js I got so far to draw the canvas:
var canvas=document.getElementById("c");
var ctx=canvas.getContext("2d");
var width=50;
var height=35;
var $width=document.getElementById('width');
var $height=document.getElementById('height');
var paneelWidth=101;
var peneelHeight=170;
$width.value=width;
$height.value=height;
draw();
$width.addEventListener("keyup", function(){
width=this.value/2;
draw();
}, false);
$height.addEventListener("keyup", function(){
height=this.value/2;
draw();
}, false);
function draw(){
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.fillRect(10,10,width,height)
}
Update
The canvas now does resize in a dynamic way based on user input.
I also found the function createPattern(), which is bringing me closer to the solution.
I've added this code to generate a pattern of solar panels in the canvas:
function placepanels(direction) {
ctx.clearRect(0, 0, canvas.width, canvas.height);
var img = document.getElementById("paneel");
var pat = ctx.createPattern(img, direction);
var w2 = canvas.width - 7;
var h2 = canvas.height - 7;
ctx.rect(7, 7, w2, h2);
ctx.fillStyle = pat;
ctx.fill();
}
The -7 on width and height is beacause I need 14cm space on each size of the canvas. Hence why I offset the rectangle containing the pattern 7px from left and top. Currently not able to achieve this on right and bottom side.
Current issue
The result I'm getting is not looking correct, it seems like the pattern repeats wrong (to much repeats) or it's not getting the proper size of the image to repeat.
Updated fiddle: https://jsfiddle.net/8e05ghqy/3/
As for the canvas resize, this function would do it:
changeCanvasSize = function( width, height ) {
$('canvas').width(width)
$('canvas').height(height)
}
Example of usage: changeCanvasSize(450,250) would change the canvas size to 450px of width and 250px of height.
I am just resizing the HTML <canvas> element .width( value ) and .height( value ) works for any HTML element.
I want to plot x and y coordinates on an image by drawing a circle around the point.
I am getting the image from the server as an array buffer. After the image is displayed i need to mark the corners in the image using coordinates sent as a json from a service.
How can i do this using javascript jquery?
I was thinking of doing the same by overlaying the image with a canvas layer.
How can i implement this?
I have tried the below method but the points were getting plotted outside the image
jQuery('#plotCoordinates').on('click',function(){
jQuery.getJSON( "plot.json", function( response ) {
console.log("response >> " ,response);
var imageCanvas = $('#imageCan');
jQuery.each(response,function(i,obj){
console.log('obj >> ',obj);
point = $('<div class="plot-point"></div>');
x = obj.x,
y = obj.y;
point.css({
left: x + "px",
top: y + "px"
});
point.appendTo(imageCanvas);
});
});
});
You can certainly do it using a canvas.Do the following steps-->
Draw image on canvas as image size=canvas size.
Now, overlay another canvas with a higher z-index exactly on the previous canvas(canvas is transparent by default).
Now use the coordinates of the points you fetched using json to mark the corners in the image by plotting them on this overlayed canvas.
Then you can draw circles around these points on the upper canvas using simple context functions.
As canvas size is same as image size these coordinates will exactly coincide and you can achieve want you want :).In short you draw your circles and markings on the upper canvas and simply draw image on the lower canvas.Easy huhh??:)
Note:Both the canvases and the image itself should be of equal dimensions to exactly coincide.
Have a look at this example https://jsfiddle.net/rbrv949d/
<canvas id="c" style="z-index: 1;"></canvas>
<canvas id="cover" style="z-index: 2;"></canvas>
JS onload
var canvas = document.getElementById('c');
var ctx = canvas.getContext('2d');
var canover=document.getElementById('cover');
var ctxover = canvas.getContext('2d');
// Create an image element
var img = new Image();
// When the image is loaded, draw it
img.onload = function () {
ctx.drawImage(img, 0, 0);
ctxover.fillRect(0,0,10,10);
ctxover.fillRect(0,20,10,10);
}
// Specify the src to load the image
img.src = "http://www.experts-exchange.com/images/experts-exchange/experts-exchange-logo.png";
canvas.width=img.width;
canvas.height=img.height;
canover.width=img.width;
canover.height=img.height;
Here , ctxover.fillRect(xposition,yposition,widthinpixels,heightinpixels)
In your case,the xposition and yposition are the one fetched from json.
You can also draw those markings on the same canvas without using the overlayed canvas.Its upto you.Provided if you clear this canvas those markings will also get cleared unlike the other case :)
I'm trying to do a responsive canvas. All my tests has been doing with a 600x600 canvas and with that height and width it works OK and paint every line correctly. The problem is that I have tried this:
#myCanvas {
background-color: #ffffff;
border:1px solid #000000;
min-height: 600px;
height: 100%;
width: 100%;
}
Just for the record, myCanvas is inside a sm-col-8.
And it looks nice on my laptop and looks nice on my phone but (because of my draw() function, because it was thinking for a square) the draw starts more like in the down-left corner (nearby) and it should start at up-right corner.
So, I don't want to change my draw() function but what I'm looking for is to reescale the canvas size. I mean: If I'm in a laptop/tablet.. with 600x600, show it at that size, but if I'm on my phone which has 384x640 show it like 300x300? I don't know if it could be a good solution.
My draw function:
function drawLines(lines,i,table,xtotal,ytotal){
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
var xIni;
var xFin;
var yIni;
var yFin;
xIni = (c.width*parseInt(lines[i][1])/xtotal);
yIni = (c.height*parseInt(lines[i][2])/ytotal);
xFin = (c.width*parseInt(lines[i][3])/xtotal);
yFin = (c.height*parseInt(lines[i][4])/ytotal);
ctx.beginPath();
ctx.moveTo(xIni,c.height-yIni);
ctx.lineTo(xFin,c.height-yFin);
ctx.lineWidth=4;
ctx.strokeStyle = colorAleatorio();
ctx.stroke();
}
With Bootstrap, use:
<canvas id="canvas" class='img-responsive' style="border: 1px solid black;"></canvas>
You can make your html Canvas responsive by using the context.scale command.
The .scale command will scale the internal coordinates system used by canvas.
This means you do not need to change any of your own drawing coordinates because canvas will automatically transform your coordinates into scaled canvas coordinates for you.
// save the original width,height used in drawLines()
var origWidth=600;
var origHeight=600;
var scale=1.00;
// reference to canvas and context
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
// call this after resizing
// send in the new maximum width,height desired
function resizeAndRedraw(newMaxWidth,newMaxHeight){
// calc the global scaling factor that fits into the new size
// and also maintains the original aspect ratio
scale=Math.min((newMaxWidth/origWidth),(newMaxHeight/origHeight))
// resize the canvas while maintaining correct aspect ratio
canvas.width=origWidth*scale;
canvas.height=origHeight*scale;
// Note: changing the canvas element's width or height will
// erase the canvas so you must reissue all your drawing commands
drawLines(lines,i,table,xtotal,ytotal);
}
// call drawLines
function drawLines(lines,i,table,xtotal,ytotal){
// scale the canvas coordinate system to the current scale
// Note: This scales the coordinates used internally
// by canvas. It does not resize the canvas element
ctx.scale(s,s);
// now do your drawing commands
// You do not need to adjust your drawing coordinates because
// the Canvas will do that for you
var xIni;
var xFin;
var yIni;
var yFin;
xIni = (c.width*parseInt(lines[i][1])/xtotal);
yIni = (c.height*parseInt(lines[i][2])/ytotal);
xFin = (c.width*parseInt(lines[i][3])/xtotal);
yFin = (c.height*parseInt(lines[i][4])/ytotal);
ctx.beginPath();
ctx.moveTo(xIni,c.height-yIni);
ctx.lineTo(xFin,c.height-yFin);
ctx.lineWidth=4;
ctx.strokeStyle = colorAleatorio();
ctx.stroke();
// restore the context to it's unscaled state
ctx.scale(-s,-s);
}
I have JavaScript code in my site.
The code is using 2 identical photos-same size, same resolution - only different colors.
First photo is black and white photo - this is what the canvas presents.
Second photo is the same only with the original colors.
I have a button that triggers JS code - which generally removes a pixel from the black and white -and paints color pixel on the canvas. At first I used Math.random for the pixel locations.
And than I decided to use it by order. No matter where it starts or begging.. as long it will go
in this order (x,y)..(x+1,y).. until maximum x.. and than (x,y+1).. until maximum x.. and so on until all the black and white photo "transformed" into the colorful photo..
for some reason I just cant make it happen.. i tried a lot of techniques..
here is demo for global understanding:
demo is working sorry - they deactivated my free host :\ hope you still understand..
here is the original code- i just changed the last function : **removeDrawRandomPixel** ..it's just playing the function there and it should be fixed..
///////////////////////global variables///////////////////
var gray_url="bwcat.jpg"; //black and white image URI
var regular_url="cat.jpg"; //regular image URI
var n=100; //number of pixels changed per click
/////////////////////////////////////
document.addEventListener("DOMContentLoaded", function(){
var c=new EditableCanvas(document.getElementById('cnvs'));
grayScaleImage=new Image();
grayScaleImage.src=gray_url;
grayScaleImage.onload=function()
{
c.drawImage(this);
}
regularImage=new Image();
regularImage.src=regular_url;
regularImage.onload=function()
{
var p=getPixelArray(this);
btn.onclick=function(){
for(var i=1;i<=n&&p.length>0;i++){
removeDrawRandomPixel(p,c);
}
}
}
},false);
//create a Pixel object
function ImagePixel(x,y,r,g,b,a)
{
this.x=x;
this.y=y;
this.r=r;
this.g=g;
this.b=b;
this.a=a;
}
//object that allows custom methods
function EditableCanvas(canvas)
{
this.canvas=canvas;
this.context=canvas.getContext('2d');
this.width=canvas.width;
this.height=canvas.height;
this.pixelImage=this.context.createImageData(1,1);
//draw an entire picture and adjust the canvas for it
this.drawImage=function(image)
{
this.width=image.width;
this.height=image.height;
this.canvas.height=image.height;
this.canvas.width=image.width;
this.context.drawImage(image,0,0);
}
//draw a single pixel, ImagePixel pixel
this.drawPixel=function(pixel)
{
this.pixelImage.data[0]=pixel.r;
this.pixelImage.data[1]=pixel.g;
this.pixelImage.data[2]=pixel.b;
this.pixelImage.data[3]=pixel.a;
this.context.putImageData(this.pixelImage,pixel.x,pixel.y);//,pixel.x,pixel.y);
}
}
//the function returns an ordered array of Pixel pixels of the image at `src`.
function getPixelArray(img)
{
var pixelArray=[];
var cnvs=document.createElement('canvas');
cnvs.width=img.width;
cnvs.height=img.width;
var context=cnvs.getContext('2d');
context.drawImage(img,0,0);
var originalData = context.getImageData(0,0,img.width,img.height).data;
for(var i=0,pixelId=0,px;i<originalData.length;i+=4)
{
px=new ImagePixel(pixelId%img.width,Math.floor(pixelId/img.width),originalData[i],originalData[i+1],originalData[i+2],originalData[i+3]);
pixelArray.push(px);
pixelId++;
}
return pixelArray;
}
//the function remove a random pixel from pixelArray and draws it on editableCnvs
function removeDrawRandomPixel(pixelArray,editableCnvs)
{
var place=Math.floor(Math.random()*pixelArray.length);
var px=pixelArray.splice(place,1)[0];
editableCnvs.drawPixel(px);
}
html :
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>canvas rules</title>
<script src="pixel.js"></script>
</head>
<body>
<canvas id="cnvs">
oh goddmamit no support
</canvas>
<button id="btn">click to convert</button>
</body>
</html>
I tried playing the last function.. because i know the answer is in the function,how to choose the pixels..
This is untested however this is what I would change the removeDrawRandomPixel function to. You are grabbing a random point in the array currently and passing it, so it could be starting on the blue component of one pixel and ending on the g component of another pixel.
//the function remove a random pixel from pixelArray and draws it on editableCnvs
function removeDrawRandomPixel(pixelArray,editableCnvs)
{
// width and height need to be the width and height of the canvas.
var width = canvas.width,
height = canvas.height,
x = Math.floor(Math.random()*width),
y = Math.floo(Math.random()*height);
var px = (y * width + x) * 4;
editableCnvs.drawPixel(px);
}
I write this html code :
<div id="container">
<canvas id="imageView" width="1181" height="1181">
<p>Unfortunately, your browser is currently unsupported by our web
application.</p>
</canvas>
<script type="text/javascript">
window.onload = function() {
var c = document.getElementById('imageView');
var cxt = c.getContext('2d');
var img = new Image();
img.src = "map.jpg";
cxt.drawImage(img, 0, 0);
};
</script>
</div>
And write this javascript :
this.mousemove = function(ev) {
if (!tool.started) {
return;
}
var x = Math.min(ev._x, tool.x0),
y = Math.min(ev._y, tool.y0),
w = Math.abs(ev._x - tool.x0),
h = Math.abs(ev._y - tool.y0);
context.clearRect(0, 0, canvas.width, canvas.height);
if (!w || !h) {
return;
}
context.clearRect(x, y, w, h);
context.strokeRect(x, y, w, h);
this code is make a rectangle . I want change this rectangle to a area map , that when I click on the area do something , (for example open google.com) .
If I understand you correctly you want to invoke a function when you hit a pixel on the actual map - not just in the map area.
Method 1
You can check a map click in more than one way. You can simply check for the pixel value at the click point to check if it is inside the area you want it to be by comparing the map color value.
I provided an example below for this method.
Method 2
You can pre-define a polygon which traces the outline of the map area you want to check.
Then build a path (ctx.beginPath(); and ctx.lineTo(..); etc.) to allow the use of the method:
if (ctx.isPointInPath(x, y)) { ... };
This is a good method if you have small regions to check.
Method 3
Store a separate image of the map containing only a matte (sort of an alpha map), That is usually black (or transparent) for non-clickable areas, white for clickable areas.
This is useful if your map is complex color-wise and a simple pixel value check is not trivial.
And speaking of which: you can even provide different solid color values for different areas so that you can define red color = USA, blue = Argentina, etc. As these are not visible to the user the only thing that matters is that the color value can be recognized (for this reason don't save images for this use with an ICC color profile).
Then project the mouse position from the click onto the matte image (which is basically an off-screen canvas where the matte image is drawn into) and check for the color (white or other color).
Example for method 1
This is a simple example, but in any case there are a couple of things you need to know in advance:
That the image is loaded from same server as the page or from a domain that allow cross-origin use. Or else you cannot grab a pixel from the map due to security reasons.
You need to know what color or alpha value to check for. If the map is solid and everything is transparent you just need to check for alpha value above zero (as in this example), and if not just check the RGB value of the region you want to trigger an action with.
ONLINE DEMO HERE
HTML:
<canvas width=725 height=420 id="demo"></canvas>
JavaScript:
var ctx = demo.getContext('2d'),
img = new Image();
/// we need to wait for the image to actually load:
img.onload = function() {
/// image is loaded and we can raw it onto canvas
ctx.drawImage(this, 0, 0);
/// enable mouse click
demo.onclick = function(e) {
/// adjust mouse position to be relative to canvas
var rect = demo.getBoundingClientRect(),
x = e.clientX - rect.left,
y = e.clientY - rect.top;
/// grab a pixel
var data = ctx.getImageData(x, y, 1, 1).data;
/// check it's alpha value to see if we're in a map point
/// this of course assumes the map has transparent areas.
/// if not just check for the color values instead.
if (data[3] > 0) alert('We hit map');
}
}
/// we need crossOrigin allowed image or we can't grab pixel later
img.crossOrigin = 'anonymous';
img.src = 'http://i.imgur.com/x8Ap3ij.png';
Just replace the alert with:
window.open('http://google.com/');
if you want it to open a new window/tab.
You can turn canvas into an anchor link by using addEventListener to listen for clicks on the canvas.
Then you can use window.open to open google in a new browser tab.
Also, you need to use image.onload to give your image time to load before using drawing it.
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var img=new Image();
img.onload=function(){
ctx.drawImage(img,0,0);
canvas.addEventListener("click",function(){
window.open("http://google.com");
});
}
img.src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/google.jpg";