I'm having my first experience in developing html5 applications. My issue is to make room plan. In the top of the page I have elements to drag to the bottom map area (they are copied). In the map area I can move elements, but not copy.
I've built drag'n'drop with help of image elements. But now I want to use canvas for updating numbers on images. I want to use canvas text functions for updating images.
The problem is when I copy canvas element from the top, html inserts well, but it is not drawn in some reasons.
Please, watch code here http://jsfiddle.net/InsideZ/MuGnv/2/. Code was written for Google Chrome.
EDIT:
I made a few small tweaks here: http://jsfiddle.net/MuGnv/5/
Note the changes made to the drawImg function:
function drawImg(src, targetClass) {
$(targetClass).each(function() {
var ctx = $(this).get(0).getContext('2d');
var img = new Image();
img.src = src;
img.onload = function() {
ctx.drawImage(img, 0, 0);
};
});
}
Anytime a drop event is handled, the images are drawn again. This was the missing component as the image was only being drawn once.
Related
I am building a web application for annotating images. The work flow is as follows:
Select a project - using : action = list all sub-projects
Click on a sub-project : action = fetch all the images within-sub project
Display the images as a horizontal scrollable thumbnail gallery
Onclick image thumbnail from the gallery, display the larger image for annotation.
I am using canvas to display larger image. I have used another canvas as a layer to the first one, and I am able to draw rectangles using mouse over regions of interest. I am saving it locally. However, when I move on to the next image, the rectangle also gets carried to the next image.
My question is, instead of using just one layer, do I have to dynamically create as many canvas layers as I have in the annotation dataset. I am not sure because in each sub project I have around 8000-9000 images. Though I wont be annotating on all of them, still creating as many canvases as layers doesn't really sound good for me.
The following is the code:
HTML Canvas
<div class="body"> <!-- Canvas to display images begins -->
<canvas id="iriscanvas" width=700px height=700px style="position:absolute;margin:50px 0 0 0;z-index:1"></canvas>
<canvas id="regncanvas" onclick="draw(this, event)" width=700px height=700px style="position:absolute;margin:50px 0 0 0;z-index:2"></canvas>
</div> <!-- Canvas to display images ends -->
Step 4 given above: OnClick display thumbnail
function clickedImage(clicked_id) {
var clickedImg = document.getElementById(clicked_id).src;
var clickedImg = clickedImg.replace(/^.*[\\\/]/, '');
localStorage.setItem("clickedImg", clickedImg);
var canvas = document.getElementById("iriscanvas");
var ctx = canvas.getContext("2d");
var thumbNails = document.getElementById("loaded_img_panel");
var pic = new Image();
pic.onload = function() {
ctx.drawImage(pic, 0,0)
}
thumbNails.addEventListener('click', function(event) {
pic.src = event.target.src;
});
}
Draw rectangles on second layer of canvas
window.onload=function(){
c=document.getElementById("regncanvas");
if (c) initCanvas(c);
};
function initCanvas(canvas){
// Load last canvas
loadLastCanvas(canvas);
}
function draw(canvas, event){
// Draw at random place
ctx=c.getContext("2d");
ctx.fillStyle="#ff0000";
ctx.beginPath();
ctx.fillRect (250*Math.random()+1, 220*Math.random()+1, 40, 30);
ctx.closePath();
ctx.fill();
// Save canvas
saveCanvas(canvas);
}
function saveCanvas(c){
localStorage['lastImgURI']=c.toDataURL("image/png");
}
function loadLastCanvas(c){
if (!localStorage['lastImgURI']) return;
img = new Image();
img.onload = function() {
ctx=c.getContext("2d");
ctx.drawImage(img, 0, 0, img.width, img.height);
};
img.src= localStorage['lastImgURI'];
}
Can someone guide me please?
The following is a screen grab of my application:
I have developed OCLAVI which is an image annotation tool with loads of features. It's still in beta but just after 3 weeks of release, it is gaining attraction quickly.
I have few advises for you.
HTML Canvas follow draw and forget strategy and every time redrawing the image is not a good idea. Be it 10 images or 10k, you should have one canvas for drawing the image and one canvas for drawing the shapes. Image canvas need be touched only when the image changes. Different shapes can share the same canvas.
You should integrate a data storage. Local storage is clearly not a good option to store this amount of data (especially if you have a team member who also would be annotating on the same image dataset.)
Isolate the code to a separate-separate file according to the shape. It will be very handy when you will think of adding support for Circle, Polygon, Cuboidal, Point interactions. Trust me following OOPs concepts will relive you from a lot of pain.
In terms of complexity
zooming with coordinates is easy
move with coordinates is of medium level difficulty
but you need to think with pen and paper to implement move on a zoomed image canvas (P.S. take care of the canvas flickering when the image moves
). How much the image can move in each direction also need to be calculated.
Take care of the image to canvas dimension ratio because at the end you need to have the coordinates scaled down to image level.
If your canvas size vs image size ratio is 1:1 then your job is simplified.
But this won't happen always because some images might be very small or very large to directly fit in window screen and you need to scale up and down accordingly.
The complexity increases if you like to use percentage width and height for canvas and your other team member annotating the image has a different screen size. So he drawing something will look something else on your screen.
Recently, Mozilla launched a HTML5 game called Browser Quest. In the game, if you resized the window, the canvas would also resize.
I looked more into and I saw that it was beacuse of usign CSS3 Media Queries found here https://developer.mozilla.org/en/CSS/Media_queries
However, I still don't think I am doing it right. My canvas ID is #canvas. How would I go about putting it for my canvas?
my canvas specific width/height: height:352px; width:512px;
So you don't want to define size of a canvas in CSS since you will only ever be scaling it away from its "true" size. You always want to use the width and height attributes of the Canvas instead.
But that doesn't mean you can't define it's parent's size that way. Wrap the canvas in a div and set the div's CSS width/height to 100% (or whatever you please)
In code during setup you are going to have to do:
// javascript pseudocode
canvas.width = theCanvasParent.clientWidth; // or whatever attribute it is, I'd reccomend putting all of those things in one giant container div
canvas.height = theCanvasParent.clientHeight;
Since most browsers do not fire an event when the parent div changes size, you'll simply have to check, say, every half second with a timer to see if the div has changed size. If it has, then you resize the canvas accordingly.
However there is the onresize event, and depending on how your page is setup this may do the trick.
In Firefox, Opera, Google Chrome and Safari, the onresize event is fired only when the size of the browser window is changed.
In Internet Explorer, the onresize event is fired when the size of the browser window or an element is changed.
So if the only way to change your div's size is by changing the window's size, onresize will do you just fine. Otherwise you'll need a timer that constantly checks to see if the canvas size and div size are different (and if so, to resize the canvas).
A timer that constantly checks is what the Mozilla Bepsin team did (before Bespin became Skywriter and then merged with the Ace project, dropping all Canvas use)
Media queries won't provide you with the functionality you seek. Their purpose is simply to limit when a particular stylesheet is applied to a page.
Furthermore, the CSS width and height properties do not adjust the actual dimensions of canvas elements. Instead, they scale the element to the requested size. In your case, I'm assuming you want the canvas to actually be a different resolution. The resolution of the canvas is specified via the DOM width and height attributes on your <canvas> tag.
In order to handle resizing, you will need to use window.onresize to capture the resize event. Your canvas code will need to then create a new canvas at the desired size and properly copy over everything from the original canvas (when you resize a canvas object its pixel data is cleared).
As was yet pointed by Xenethyl, the most important point is to hook onresize so that you can adapt to your new canvas object size :
adjust the canvas dimensions (the drawing area dimensions) to the canvas rendering area (clientWidth and clientHeight)
take into account the new dimensions of the canvas for your drawing algorithms
redraw the canvas
You don't have to make a new canvas (which would force you to rehook other event handlers).
Most of the canvas in my web applications, in order to be perfectly adjusted to the window, are managed by a dedicated class whose skeleton is here :
function Grapher(options) {
this.graphId = options.canvasId;
this.dimChanged = true; // you may remove that if you want (see above)
};
Grapher.prototype.draw = function() {
if (!this._ensureInit()) return;
// makes all the drawing, depending on the state of the application's model
// uses dimChanged to know if the positions and dimensions of drawed objects have
// to be recomputed due to a change in canvas dimensions
}
Grapher.prototype._ensureInit = function() {
if (this.canvas) return true;
var canvas = document.getElementById(this.graphId);
if (!canvas) {
return false;
}
if (!$('#'+this.graphId).is(':visible')) return false;
this.canvas = canvas;
this.context = this.canvas.getContext("2d");
var _this = this;
var setDim = function() {
_this.w = _this.canvas.clientWidth;
_this.h = _this.canvas.clientHeight;
_this.canvas.width = _this.w;
_this.canvas.height = _this.h;
_this.dimChanged = true;
_this.draw(); // calls the function that draws the content
};
setDim();
$(window).resize(setDim);
// other inits (mouse hover, mouse click, etc.)
return true;
};
In your case I would create a new Grapher({canvasId:'#canvas'}) and the #canvas dimensions are defined in css (and usually adjust in complex ways to the available space).
The most interesting points are in the setDim function.
I've two different stages on top of another.
And, I'm adding layers to them and placed two image objects.
Now, I've given "click" event to those image objects.
However, since recently added layer is on top of other layers, Only top layer is triggering the events.
Problem : Clicking on purple indicator , I'm getting the alert. But, yellow indicator does not trigger any event since it is behind the layer.
(Check JSFiddle Link which is provided at the bottom)
How to overcome this issue..?
Here is the code sample that I'm using to add & position the image.
Working JS Fiddle Link : http://jsfiddle.net/v4u2chat/aqf9Y/8/
NOTE : Use the Slider to change the position of the image.
Image Positioning Code
$function positionImage(stage,centerX,centerY,radius,startingAngle,endingAngle,targetValue4ImagePositioning,divIdvalue)
{
var imgLayer = new Kinetic.Layer();
var angleInDegress = 360*targetValue4ImagePositioning-90-5;
var angleInRadians = (Math.PI/180)*angleInDegress;
imgLayer.rotate((Math.PI/180)*(360*targetValue4ImagePositioning));
var arcEndX = centerX+ ((radius+25)*Math.cos(angleInRadians));
var arcEndY = centerY+ ((radius+25)*Math.sin(angleInRadians));
imgLayer.setX(arcEndX);
imgLayer.setY(arcEndY);
var kineticImage = new Kinetic.Image(
{
x: 0
,y: 0
,width:18
,height:22
,image: $('#'+divIdvalue)[0]
,id:'kineticImage_'+divIdvalue
});
kineticImage.on("click", callBackFn);
imgLayer.add(kineticImage);
stage.add(imgLayer);
}
Thanks **Steve** for your input.
The actual problem lies in Stage. I'm using two different stages which is not required.
Now, I changed my code to single Stage and it works like charm :)
Layer will not occupy the whole canvas area. It'll occupy only the area of the shape for which we have created the layer. So, No fuss or problem with Layers.
Updated JS Fiddle can be found from the below mentioned link.
http://jsfiddle.net/v4u2chat/aqf9Y/9/
I want to play animated GIF file inside a HTML Canvas. I have used the code below but it is not working.
What is wrong with the code?
var drawingCanvas = document.getElementById('myDrawingCanvas');
if(drawingCanvas.getContext)
{
var context = drawingCanvas.getContext('2d');
var imgObj = new Image();
imgObj.onload = function ()
{
context.drawImage(imgObj, 0, 0, 1024, 600);
}
imgObj.src='HTML Images/Spell Bee/images/mainscreen.gif';
}
You cannot as canvas doesn't provide any methods to deal with animated gifs. You should split gif into single frames then create a spritesheet and animate it copying current frame.
You can actually decode the GIF with JavaScript and write the frames to canvas. Check http://slbkbs.org/jsgif/
I found an article that answers your question. Basically, when you add an animated gif to a canvas element it displays the exact state the image is at when it's included. So, as rezoner says, you need to create a spritesheet and animate it using javascript.
I'm making a little thing in AS3, a "wanted" poster generator. I load the webcam inside my poster ("container") and put an attributesContainer next to it. There I have a hat, a mustache, ... people can drag and drop on the webcam instance. No problem here, but now I want to send it to Facebook. I know how that works, but I'm having some difficulties with keeping the position of the hat/mustache/... where the user wanted it.
For example: I drag the hat onto my head (middle of the poster), I hit the "take picture" button to draw Bitmapdata, and my hat is at coordinates 0,0 again. I believe I have to work with a Matrix, but I tried everything now and it just doesn't show up or stays at 0,0.
Any help? Here's some of my code.
private function sendHandler(e:MouseEvent):void {
var bmd:BitmapData;
var bmp:Bitmap;
// "container" contains poster+webcam img
bmd = new BitmapData(container.width, container.height, true);
bmd.draw(container);
//var hatMatrix:Matrix = new Matrix(1, 0, 0, 1, hat.x, hat.y);
bmd.draw(hat);
bmp = new Bitmap(bmd, "auto", true);
sendToFacebook();
}
You can make your life a little easier by structuring it different.
Have a top level container.
Add to that your webcam display
Also add to that your dropped items
Then you can just take a bitmap of the top level container instead of each piece and compositing them together.