I have searched a lot, but I could not find a scenario which is relevant to my need. I want to drag and drop images from a toolbar to a canvas, not from a canvas to another canvas.
Please help me on this. Thanks in advance
Demo: http://jsfiddle.net/m1erickson/2Us2S/
Use jquery-ui to create draggable elements.
$("#myToolbarImageElement").draggable();
Load these elements with data payloads which are key-value pairs.
In your case this might be an image object that you want drawn on the canvas.
$("#myToolbarImageElement").data("image",myImageObject);
Set your canvas as a drop zone:
$("#myCanvas").droppable({drop:myDropHandler});
When you drop the elements on canvas you can read the data (image) and drawImage that image to the canvas.
function myDropHandler(e,ui){
var x = ui.offset.left - $("#myCanvas").offset.left;
var y = ui.offset.top - $("#myCanvas").offset.top;
var image = ui.draggable.data("image");
// draw on canvas
drawImage(image,x,y);
}
Here's a nice tutorial on drag-drop elements with data payloads using jquery-ui:
http://www.elated.com/articles/drag-and-drop-with-jquery-your-essential-guide/
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.
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 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.
I have a canvas with the following size: 500x200. Inside this canvas i'm drawing some number of blocks (actually - table cells). Information about how much blocks i should draw i'm getting via AJAX, but size for every cell is fixed - 100x50. So, i can display inside my canvas only 5 blocks horizontally and 4 vertically. But what about other blocks? What if script return a table 30x30 cells. How can i side scroll (mouse preferred) my canvas so user can the rest of the cells (no zoom out, only scrolling).
If you need any more information, please, tell me and i will provide it.
Thank you.
The easiest way to accomplish this is to implement mouse-panning.
On the mouse down event, begin panning and save the mouse position
On the mouse move event, translate the context (ctx.translate(x,y)) by the difference between the current mouse position and the original position, then redraw the scene.
On the mouse up event, stop panning.
There are harder ways. You could implement scrollbars inside the canvas, as Mozilla Bespin has done (...which became Mozilla Skywriter which then merged with Ace and dropped all Canvas use). The code that they used was pretty good.
Or you could implement DOM scrollbars for use with your canvas, which isn't exactly easy to get right in all cases. This involves adding several dummy divs in order to give the appearance and function of real scrollbars. I have done this but the code remains unreleased for now. But thats no reason you can't give it a try if thats what you really want.
Check out a great tutorial at: http://www.brighthub.com/hubfolio/matthew-casperson/blog/archive/2009/06/29/game-development-with-javascript-and-the-canvas-element.aspx
It will give you an answer to your question and much much more...
I'm with Simon Sarris on this, but as an alternative, you could clone the canvas, and replace it with a blank canvas, and then render the original canvas as an image. I've some MooTools js that goes like this, which is fine for my use, by ymmv:
var destinationCanvas = this.canvas.clone()l
destinationCanvas.cloneEvents( this.canvas, 'mousemove');
var destCtx = destinationCanvas.getContext('2d');
destCtx.drawImage(
this.canvas,
(this.options.scrollPx)*-1,
0
);
destinationCanvas.replaces( this.canvas );
this.canvas.destroy();
this.canvas = destinationCanvas;
this.ctx = destCtx; // this.canvas.getContext('2d');