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I'm working with vis.js to display some graphs. The problem is that layouts with multiple central nodes get noisy (the central nodes' neighbours overlap). A layout similar to the attached image is desirable.
Is it possible to achieve this using vis.js?
Looks like there is an option that should solve your issue (I've found it after playing with physicsConfiguration like I suggested earlier):
physics has avoidOverlap property (float between 0 and 1) that can be used like this:
var options = {
...
physics: {
barnesHut: {
avoidOverlap: 0.5
},
...
}
}
If you try it in the configuration demo, you'll see that with avoidOverlap equal to 0 it's quite possible to drag and move nodes so that those overlap edges and the network stays in that position:
but once we increase this value, nodes start to be bounced from edges and can't really stay in that position:
Note though, that this option doesn't prevent edge-edge crossing, only edge-node overlapping (see physics/barnesHut/avoidOverlap). The physics docs page doesn't contain the word "cross" at all and each occurance of "overlap" is about edge-node thing.
So this will make the layout less noisy, but won't eliminate crossed edges.
I am making a web app to show relationships between items using Vis.js, everything works perfectly fine until I get to the point where I need to display ~260 nodes with ~1200 edges between them.
Once I get to that amount of nodes, the graph just shows a blank space and a blue line, nothing else. As soon as I try to zoom it, the line disappears and it's all white.
When I look at the position of the nodes I can see that many of them are in negative or very big x, y positions (generally -300 for x and around 478759527705558300000 for y).
I have tried, to no avail, to disable physics. The graph is in hierarchichal mode, with levels manually set in the code, but the levels are correct.
Network options (the improvedLayout option was just a possibility I found on the internet; it works just the same if I remove it):
var options = {
layout: {
improvedLayout: false,
hierarchical: {
direction: direction,
sortMethod: "directed"
}
}
}
Screenshot:
I have hierarchical layout graph which consists of around 615 nodes and 614 edges (excluding 40 odd cluster nodes, some of them cluster of clusters). I landed into same problem with visjs.
One quick thing which helped me to get over this problem was to explicitly call network.stabilize() method with an argument specifying number of iterations. Default iterations are 1000. I passed 10000 and graph stabilized it self nicely. It took a few more seconds, i was fine with that. But stabilization times shoots up as number nodes increased to ~1000. So i started looking into visjs code for solution.
While looking in visjs code, i found that inside function setupHierarchicalLayout() there is a call to _condenseHierarchy().
This method tries to minimize white spaces between nodes and edges (yet to understand the code fully). _condenseHierarchy() modifies coordinates of a node. See Y coordinate before and after call to _condenseHierarchy() below:
(this.body.nodes["node-11"]).y
1530
(this.body.nodes["node-11"]).y
64920
When a node gets a distant position it takes lots of iterations (in stabilize) to bring it closer together with other nodes in graph. I disabled _condenseHierarchy() and got the graph displayed nicely.
I'm sure disabling _condenseHierarchy() would bring in some other issues as i proceed further. I am going to spend some more time to understand and experiment with _condenseHierarchy().
To solve this problem, you can adjust hierarchical layout parameters, such as nodeSpacing, levelSeparation and treeSpacing. Here is an example hierarchicalLayoutWithoutPhysics
I have a pre-defined-size rectangular area with some other rectangles inside, which represents filled regions, or, let say, obstacles.
All the rectangles are axis-aligned.
Origin of the axis (i.e. 0,0) is top-left.
The X and Y coordinates of all the rectangles, as well as the horizontal and vertical size is known.
Information about the rectangles inside the main area is contained in an already-sorted array, where i[0],i[1] are the X,Y coordinates of the upper-left corner and i[2],i[3] are respectively the x and y size:
[
[10,1,14,7],
[34,1,14,15],
[16,22,27,44]
]
How can i get all the rectangles covering the free remaining space, like in the image below?
(credits: Jukka Jylänki, A Thousand Ways to Pack the Bin - A Practical Approach to Two-Dimensional Rectangle Bin Packing http://clb.demon.fi/)
I don't need an algorithm for optimal bin-packing, as the rectangles are already placed, nor to find the biggest rectangle, but i'm aware that these can be related arguments.
I have also read some papers about the line-sweep algorithm, but i'm not able to get a working implementation, and so i cannot imagine if this would be the right solution for my problem.
My first attempt (clearly wrong) was to gather all the cuts generated by all the sides (inverse intersection):
[
[24,8,37,8],
[1,16,60,6],
[1,22,15,44],
[43,22,18,44],
[1,66,60,5],
[1,1,9,70],
[10,16,6,55],
[24,1,10,21],
[34,8,9,14],
[43,8,5,63],
[48,1,13,70]
]
...but this would require an additional step to to join adjacent rectangles and then filter out those inside a bigger one. See for example, the red-marked rectangles in this picture:
Could be this a way to go, though not optimized?
I've built a canvas library for managing scenes of shapes for some work projects. Each shape is an object with a drawing method associated with it. During a refresh of the canvas, each shape on the stack is drawn. A shape may have typical mouse events bound which are all wrapped around the canvas' own DOM mouse events.
I found some techniques in the wild for detecting mouseover on individual shapes, each of which works but with some pretty serious caveats.
A cleared ghost canvas is used to draw an individual shape by itself. I then store a copy of the ghost canvas with getImageData(). As you can imagine, this takes up a LOT of memory when there are many points with mouse events bound (100 clickable shapes on a 960x800 canvas is ~300MB in memory).
To sidestep the memory issue, I began looping over the pixel data and storing only addresses to pixels with non-zero alpha. This worked well for reducing memory, but dramatically increased the CPU load. I only iterate on every 4th index (RGBA), and any pixel address with a non-zero alpha is stored as a hash key for fast lookups during mouse moves. It still overloads mobile browsers and Firefox on Linux for 10+ seconds.
I read about a technique where all shapes would be drawn to one ghost canvas using color to differentiate which shape owned each pixel. I was really happy with this idea, because it should theoretically be able to differentiatate between millions of shapes.
Unfortunately, this is broken by anti-aliasing, which cannot be disabled on most canvas implementations. Each fuzzy edge creates dozens of colors which might be safely ignored except that /they can blend/ with overlapping shape edges. The last thing I want to happen when someone crosses the mouse over a shape boundary is to fire semi-random mouseover events for unrelated shapes associated with colors that have emerged from the blending due to AA.
I know that this not a new problem for video game developers and there must be fast algorithms for this kind of thing. If anyone is aware of an algorithm that can resolve (realistically) hundreds of shapes without occupying the CPU for more than a few seconds or blowing up RAM consumption dramatically, I would be very grateful.
There are two other Stack Overflow topics on mouseover detection, both of which discuss this topic, but they go no further than the 3 methods I describe.
Detect mouseover of certain points within an HTML canvas? and
mouseover circle HTML5 canvas.
EDIT: 2011/10/21
I tested another method which is more dynamic and doesn't require storing anything, but it's crippled by a performance problem in Firefox. The method is basically to loop over the shapes and: 1) clear 1x1 pixel under mouse, 2) draw shape, 3) get 1x1 pixel under mouse. Surprisingly this works very well in Chrome and IE, but miserably under Firefox.
Apparently Chrome and IE are able to optimize if you only want a small pixel area, but Firefox doesn't appear to be optimizing at all based on the desired pixel area. Maybe internally it gets the entire canvas, then returns your pixel area.
Code and raw output here: http://pastebin.com/aW3xr2eB.
If I understand the question correctly, you want to detect when the mouse enters/leaves a shape on the canvas, correct?
If so, then you can use simple geometric calculations, which are MUCH simpler and faster than looping over pixel data. Your rendering algorithm already has a list of all visible shapes, so you know the position, dimension and type of each shape.
Assuming you have some kind of list of shapes, similar to what #Benjammmin' is describing, you can loop over the visible shapes and do point-inside-polygon checks:
// Track which shape is currently under the mouse cursor, and raise
// mouse enter/leave events
function trackHoverShape(mousePos) {
var shape;
for (var i = 0, len = visibleShapes.length; i < len; i++) {
shape = visibleShapes[i];
switch (shape.type ) {
case 'arc':
if (pointInCircle(mousePos, shape) &&
_currentHoverShape !== shape) {
raiseEvent(_currentHoverShape, 'mouseleave');
_currentHoverShape = shape;
raiseEvent(_currentHoverShape, 'mouseenter');
return;
}
break;
case 'rect':
if (pointInRect(mousePos, shape) &&
_currentHoverShape !== shape) {
raiseEvent(_currentHoverShape, 'mouseleave');
_currentHoverShape = shape;
raiseEvent(_currentHoverShape, 'mouseenter');
}
break;
}
}
}
function raiseEvent(shape, eventName) {
var handler = shape.events[eventName];
if (handler)
handler();
}
// Check if the distance between the point and the shape's
// center is greater than the circle's radius. (Pythagorean theroem)
function pointInCircle(point, shape) {
var distX = Math.abs(point.x - shape.center.x),
distY = Math.abs(point.y - shape.center.y),
dist = Math.sqrt(distX * distX + distY * distY);
return dist < shape.radius;
}
So, just call the trackHoverShape inside your canvas mousemove event and it will keep track of the shape currently under the mouse.
I hope this helps.
From comment:
Personally I would just switch to using SVG. It's more what it was
made for. However it may be worth looking at EaselJS
source. There's a method Stage.getObjectUnderPoint(), and their demo's
of this seem to work perfectly fine.
I ended up looking at the source, and the library utilises your first approach - separate hidden canvas for each object.
One idea that came to mind was attempting to create some kind of a content-aware algorithm to detect anti-aliased pixels and with what shapes they belong. I quickly dismissed this idea.
I do have one more theory, however. There doesn't seem to be a way around using ghost canvases, but maybe there is a way to generate them only when they're needed.
Please note the following idea is all theoretical and untested. It is possible I may have overlooked something that would mean this method would not work.
Along with drawing an object, store the method in which you drew that object. Then, using the method of drawing an object you can calculate a rough bounding box for that object. When clicking on the canvas, run a loop through all the objects you have on the canvas and extract ones which bounding boxes intercept with the point. For each of these extracted objects, draw them separately onto a ghost canvas using the method reference for that object. Determine if the mouse is positioned over a non-white pixel, clear the canvas, and repeat.
As an example, consider I have drawn two objects. I will store the methods for drawing the rectangle and circle in a readable manner.
circ = ['beginPath', ['arc', 75, 75, 10], 'closePath', 'fill']
rect = ['beginPath', ['rect', 150, 5, 30, 40], 'closePath', 'fill']
(You may want to minify the data saved, or use another syntax, such as the SVG syntax)
As I am drawing these circles for the first time, I will also keep note of the dimensional values and use them to determine a bounding box (Note: you will need to compensate for stroke widths).
circ = {left: 65, top: 65, right: 85, bottom: 85}
rect = {left: 150, top: 5, right: 180, bottom: 45}
A click event has occurred on the canvas. The mouse point is {x: 70, y: 80}
Looping through the two objects, we find that the mouse coordinates fall within the circle bounds. So we mark the circle object as a possible candidate for collision.
Analysing the circles drawing method, we can recreate it on a ghost canvas and then test if the mouse coordinates fall on a non-white pixel.
After determining if it does or does not, we can clear the ghost canvas to prepare for any more objects to be drawn on it.
As you can see this removes the need to store 960 x 800 x 100 pixels and only 960 x 800 x2 at most.
This idea would best be implemented as some kind of API for automatically handling the data storage (such as the method of drawing, dimensions...).
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.