1) I'm caching a container filled with objects and then getting the canvas with .cacheCanvas in easel. I use this canvas as a bitmap image for my background (for performance reasons).
2) When I want to make minor changes to the image, rather than re-caching the large container, I get the context('2d') of the cachedCanvas(that I store in an easel Bitmap() ) and I draw onto the cachedCanvas.
The issue i'm having is when I draw onto the context of a cachedCanvas, it seems like the canvas is shared with the container and the bitmap, so when I do step 2) all of the imageDraws that I do are also done to the container. After repeating step 1) I want just the container and it's objects. (Not all of the context.draws that I did in step 2) )
TLDR: Is there a proper way to draw on a cachedCanvas, but also have the ability to revert to the original cachedCanvas?
This was solved by using uncache();
Related
I would like to create an element, that shows a red circle. Once the user clicks on it, she can record her voice. In order to show the LIVE mode, I'd like to make the circle "breath" according to the incoming frequencies.
I'm experimenting with a <canvas> element. That means it creates a circle that gets bigger and smaller, depending on the variable arcrad. However, the lines are being drawn correctly, but they do not disappear afterwards. I tried to apply .clip() but can't get it to work...
if (arcrad <= 10) arcrad = 10;
analyserContext.beginPath();
analyserContext.arc(100,120,arcrad,0,2*Math.PI);
analyserContext.closePath();
analyserContext.lineWidth = 2;
analyserContext.strokeStyle = 'red';
analyserContext.stroke();
Any ideas - or completely different strategies for this use case?
Canvas will overdraw by default. For your animation you’ll need to clean the canvas at the start of each frame. Use something the following at the start of your drawing function:
analyserContext.clearRect(0,0,200,200);
assuming your canvas is 200 pixels wide and high. It’s worth pointing out that sometimes you don’t want to completely clear the animation field every frame. For example, if you were to draw a semi transparent rectangle over the frame at the beginning (instead of clearing it) then you’d end up with a basic ‘bullet time’ style effect.
It's a normal behavior. Once something it's drawn on the canvas, it's there forever. You have to think like if you were painting something: what has been done cannot be undone.
Luckily, you still have solutions:
1) redraw another circle on top of the first one with the background color. It's really not the recommend way, but it still can be useful
2) use clearRect method (see How to clear the canvas for redrawing)
There are numerous ways to clear a canvas pre drawing to create animation:
How to clear the canvas for redrawing
simplest in my mind:
canvas.width=canvas.width;
though can equally use clearRect (which is actually quicker and won't reset the entire canvas if that is an issue regarding transforms etc!) over the region or whole canvas.
Get the likes of:
http://jsfiddle.net/dw17jxee/
I have a polygon object (say a car) drawn inside a HTML5 canvas with help of methods moveTo and lineTo. I want to repeatedly draw that object at different positions in the canvas (simulating a moving object). My problem is that the previous drawn object is not getting cleared. Instead, multiple images are drawn on the canvas. How can I fix this issue?
You have to clear the canvas at the start of every draw frame
context.clearRect(0, 0, canvas.width, canvas.height);
Canvases are just arrays of pixels, they know nothing of the shapes you have drawn.
There are animation tricks that used to be used on bitmapped displays (e.g. "xor drawing") that can be used to remove the old shape before you draw the new one, but on modern machines it's generally far simpler (and perfectly fast) to just erase the canvas and start again for each frame.
Given your comments to other answers, I'd suggest just using two Canvases - one for the static background and one for the car. If the background image is static it could even be an <img> element instead of a Canvas.
If the car image is static you could also just draw that once, and then use CSS positioning to set its position relative to the background for each frame.
suppose your shape is car then you first have to assign a new graphic like:
car.graphics = new createjs.Graphics();
car.graphics
.setStrokeStyle(1)
.beginStroke("#000000")
.moveTo()
.lineTo()
.lineTo()
I am currently working on a "Photo Collage Maker" project which needs larger canvas area and hundreds of objects(text, images, shapes, clip-arts etc.). The problem is while moving, scaling and rotating those objects, Fabric.js render all the objects which makes it too slow. I want to render only the selected objects on top of the fabric canvas. I have tested renderOnAddition, renderTop also but they are not what I want.
I want the following:
canvas.on('object:moving', function(e) {
var activeObject = e.target;
//canvas.renderAll();
canvas.renderObjects(activeObject);
});
Now instead of canvas.renderAll(), I need method like canvas.renderObjects(activeObject). How can I achieve this functionality in Fabric.js?
Here is my project : Edit Photos For Free
Your best bet is to have a second canvas, in front of the main one, on which you move/scale/rotate the current item(s).
You mention wanting to render the selected objects on top of the fabric canvas, so this should meet your requirements.
On ending the move/scale/rotate you will have to restore the original canvas elements, apply your changes, and allow it to do a full redraw.
May be there are many renderAll() methods
Chech if that is case you need to use requestRenderAll() method
I am looking for a way to capture the complete canvas (including elements that are moved outside the canvas) to an image. I am using the KineticJS library and I am aware of the toDataURL function. The problem is that the image is clipped to the canvas bounds.
As a workaround I thought to copy all elements on the canvas to a temporary hidden canvas which is big enough to fit all elements and then use the toDataURL function. I was wondering if there is a cleaner approach?
Interesting problem. I like the temporary canvas idea. Also, you could just resize the main canvas, apply an offsetting translation to all child elements, capture the image, then reverse-translate and resize back. This wouldn't be any more complex than copying to a hidden canvas. Plus, the single canvas approach would be more memory efficient.
Just my 3 cents.
I would agree with Alvin, you could just resize the canvas, here's how:
stage.setWidth(window.innerWidth); // inner width of your window
stage.setHeight(window.innerHeight); // inner height of your window
stage.draw(); //redraw
This would resize your stage to the width and height of your window, but this would not account for the possibility that elements would be farther than your window, but you can just modify the number inside the .set functions to account for the farthest right/left one.
If you were looking for a quick way to copy all elements in your canvas to another stage you could serialize it:
var json = stage.toJSON();
var newStage = Kinetic.Node.create(stageJson, 'newContainer');
I've built an analytical data visualization engine for Canvas and have been requested to add tooltip-like hover over data elements to display detailed metrics for the data point under the cursor.
For simple bar & Gaant charts, tree graphs and node maps with simple square areas or specific points of interest, I was able to implement this by overlaying absolutely-positioned DIVs with :hover attributes, but there are some more complicated visualizations such as pie charts and a traffic flow rendering which has hundreds of separate areas defined by bezeir curves.
Is is possible to somehow attach an overlay, or trigger an event when the user mouses over a specific closed path?
Each area for which hover needs to be specified is defined as follows:
context.beginPath();
context.moveTo(segmentRight, prevTop);
context.bezierCurveTo(segmentRight, prevTop, segmentLeft, thisTop, segmentLeft, thisTop);
context.lineTo(segmentLeft, thisBottom);
context.bezierCurveTo(segmentLeft, thisBottom, segmentRight, prevBottom, segmentRight, prevBottom);
/*
* ...define additional segments...
*/
// <dream> Ideally I would like to attach to events on each path:
context.setMouseover(function(){/*Show hover content*/});
// </dream>
context.closePath();
Binding to an object like this is almost trivial to implement in Flash or Silverlight, since but the current Canvas implementation has the advantage of directly using our existing Javascript API and integrating with other Ajax elements, we are hoping to avoid putting Flash into the mix.
Any ideas?
You could handle the mousemove event and get the x,y coordinates from the event. Then you'll probably have to iterate over all your paths to test if the point is over the path. I had a similar problem that might have some code you could use.
Looping over things in this way can be slow, especially on IE. One way you could potentially speed it up - and this is a hack, but it would be quite effective - would be to change the color that each path is drawn with so that it is not noticeable by humans but so that each path is drawn in a different color. Have a table to look up colors to paths and just look up the color of the pixel under the mouse.
Shadow Canvas
The best method I have seen elsewhere for mouseover detection is to repeat the part of your drawing that you want to detect onto a hidden, cleared canvas. Then store the ImageData object. You can then check the ImageData array for the pixel of interest and return true if the alpha value is greater than 0.
// slow part
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.fillRect(100,100,canvas.width-100,canvas.height-100);
var pixels = ctx.getImageData(0,0,canvas.width,canvas.height).data;
// fast part
var idx = 4 * (mouse_x + mouse_y * canvas.width) + 3;
if (pixels[idx]) { // alpha > 0
...
}
Advantages
You can detect anything you want since you're just repeating the context methods. This works with PNG alpha, crazy compound shapes, text, etc.
If your image is fairly static, then you only need to do this one time per area of interest.
The "mask" is slow, but looking up the pixel is dirt cheap. So the "fast part" is great for mouseover detection.
Disadvantages
This is a memory hog. Each mask is W*H*4 values. If you have a small canvas area or few areas to mask, it's not that bad. Use chrome's task manager to monitor memory usage.
There is currently a known issue with getImageData in Chrome and Firefox. The results are not garbage collected right away if you nullify the variable, so if you do this too frequently, you will see memory rise rapidly. It does eventually get garbage collected and it shouldn't crash the browser, but it can be taxing on machines with small amounts of RAM.
A Hack to Save Memory
Rather than storing the whole ImageData array, we can just remember which pixels have alpha values. It saves a great deal of memory, but adds a loop to the mask process.
var mask = {};
var len = pixels.length;
for (var i=3;i<len;i+=4) if ( pixels[i] ) mask[i] = 1;
// this works the same way as the other method
var idx = 4 * (mouse_x + mouse_y * canvas.width) + 3;
if (mask[idx]) {
...
}
This could be done using the method ctx.isPointInPath, but it is not implemented in ExCanvas for IE.
But another solution would be to use HTML maps, like I did for this little library : http://phenxdesign.net/projects/phenx-web/graphics/example.htm you can get inspiration from it, but it is still a little buggy.
I needed to do detect mouse clicks for a grid of squares (like cells of an excel spreadsheet). To speed it up, I divided the grid into regions recursively halving until a small number of cells remained, for example for a 100x100 grid, the first 4 regions could be the 50x50 grids comprising the four quadrants.
Then these could be divided into another 4 each (hence giving 16 regions of 25x25 each).
This requires a small number of comparisons and finally the 25x25 grid could be tested for each cell (625 comparisons in this example).
There is a book by Eric Rowell named "HTML5 CANVAS COOKBOOK". In that book there is a chapter named "Interacting with the Canvas: Attaching Event Listeners to Shapes and Regions". mousedown, mouseup, mouseover, mouseout, mousemove, touchstart, touchend and touchmove events can be implemented. I highly suggest you read that.
This can't be done (well, at least not that easily), because objects you draw on the canvas (paths) are not represented as the same objects in the canvas. What I mean is that it is just a simple 2D context and once you drawn something on it, it completely forgets how it was drawn. It is just a set of pixels for it.
In order to watch mouseover and the likes for it, you need some kind of vector graphics canvas, that is SVG or implement your own on top of existing (which is what Sam Hasler suggested)
I would suggest overlaying an image map with proper coordinates set on the areas to match your canvas-drawn items. This way, you get tooltips AND a whole lot of other DOM/Browser functionality for free.