I'm building an application based on Paper.js.
I have a list of items, each composed from a top level group and a bunch of paths as children.
I need to implement collision detection, which currently works like so:
When an item is dragged, its components (the paths it's comprised of) are checked against any other path in the same layer using the
Path#getIntersections(path) method.
If the method returns a non empty array (of CurveLocations, which describe the points of intersection) I know there's a collision. I
stop dragging and combine the items.
If the returned array is empty, there's no collision to handle so no need to interrupt the drag. I translate (move) the dragged item by
the distance it was dragged.
And now, here's what I need to do in step 2:
Upon detecting a collision, I need to move the item to the nearest
"legal" position (the closest to the current mouse position without
overlapping any other shape/border).
Now I can go about implementing SAT or GJK and solving it without the getIntersections method, but the only thing I'm lacking here is the MTV (if I'm not mistaken).
Can someone please confirm if this is either possible or not, and if it is, then how?
Update
After some fiddling with the various mouse events, I've come to a current (imperfect) solution:
onMouseDown: Save the mouse offset (item position minus mouse position)
onMouseDrag: Check for intersections. If so, translate the dragged object by event.delta.negate() while the check returns true. When done, update the offset.
If no intersection is detected, just move the dragged item to the mouse position minus offset.
onMouseUp: The same as in the drag event, except if no collision is detected then do nothing.
This is more or less working, except it's jittery and it doesn't deal with containment.
Will update with an example as time permits.
If you only have two shapes and they are all quite close to circles and boxes and have similar sizes you could get the center of the bounding box of the shapes and use those center points as a direction vector. Then you move it incrementally away until there is no intersection anymore. But if you have shapes like a U or O that surround another smaller shape it is likely that this method will not give the shortest distance. The same if the moving away will hit other objects.
So I think what you really need is a numerical solution that moves the shape away from its center point in a circular fashion with growing diameter until there wont be any intersections anymore.
Another problem could be when your shape is enclosed in another shape and you will not even have any intersections. So I guess it would be better to use hittest.
Edit:
Here is a very easy not very well optimized example of what I tried to explain with the middle points. Reload it if you do not see any overlays. For the circular way the checking just gets more complicated because you would move the shape not only away but also in all other kind of directions.
Edit2: Second example that checks for intersection and moves the shape outside. As you can see intersection alone is not enough to check for if the obstacle gets bigger than the dragged item.
Related
Found a lot of physic engines out there but nothing that fit my needs directly.
I try to to find a simple way to push and pull boxes including collision detection which respects the next neighboring mesh hit while moving.
Some use cases to understand:
All boxes except box 1 are moveable.
Push or Pull box 4 to west:
Should move box 3 to west on collision.
Should make box 3 and 4 not able to move west when box 3 hits box 2.
Push 2, 3 or 4 to north:
Should stop when it hits box 2, because box 1 is not movable.
it should not possible to push or pull 2 colliding boxes with a box.
Maybe not the best question... I could write such a logic from scratch but this would end in fairly complex code :) and I wonder if nobody solved something like that before.
Does there exist an easy way to implement such a logic using an existing physic engine or a three.js plugin?
Hope the question is formulated well enough so that anyone can understand it.
Maybe easier If you know the famous boulder dash game.
Possible to move both rocks in both directions.
Impossible to move a rock.
In my case it should be possible to move 2 colliding rocks/cubes but not 3.
So basically you want to make certain objects immovable at various points. You can do this with physi.js. Just increase the mass of the object so it becomes so heavy relative to the other objects that it is immovable.
Pretty simple, it's more about geometry and logic than physics... if I understand your simplified world.
In the case of boulderdash (or also sokoban), where the movement is tiled-based, when you are about to move the character you first check the adjacent tile, in the direction of the movement. It could be walkable or occupied by a movable object (or also a wall). If there's a movable object, then you check the next adjacent tile. If it's walkable then means the movable object it's indeed movable. Otherwise, that movable object is currently not movable.
In a non-tiled scenario like yours seems, you check for collision with a first box and, when this happens, you check the presence of a next colliding box, adding a new colision point the size of the first box, in the direction of the movement.
I just answered a similar question here.
You should use bounding boxes of type THREE.Box3 for this purpose.
You should definitely check this example out. I think it will be very useful for you.
I'm building a canvas paint tool where the use simply drags his mouse to draw on the canvas. As I understand it lines is the best way for the job. So on mouse down I create a KineticJS Line object and when the user drags I add a point between the last mouse position and the current. Note, I only have one line object that has multiple points.
When the user releases his mouse the Line is finished and whenever you click again to draw more, I create a new line object.
Problem with this is that if you are going to draw a text, say "My name is x" That would result in many line objects, 1 for each character (and 2 for "x" and "i").
Is there a better way to do this? My idea was to have only one line object, and onmousedown you simply not add a line from the previous position, and then when u drag you do. But I don't think KineticJS Line supports that.
So basically, can I improve the way I let the user draw?
Your current design of having 1-2 polylines that define one letter is fine.
Both canvas and Kinetic can support a whole paragraph of characters before lagging in performance.
If you want 1 single definition for a whole sentence, you can use a custom Kinetic.Shape.
With Shape, you get full access to a wrapped canvas context. You could use that context to do your second idea--a single context.path drawing a sentence through a saved set of moveTo and lineTo commands.
Personally I would go with your current design (1-2 polylines per character) because the performance is fine and you get more flexibility. (For example, if you want to draw the person's name in a different color is easier in your current design).
I am working on this browser-based experiment where i am given N specific circles (let's say they have a unique picture in them) and need to position them together, leaving as little space between them as possible. It doesn't have to be arranged in a circle, but they should be "clustered" together.
The circle sizes are customizable and a user will be able to change the sizes by dragging a javascript slider, changing some circles' sizes (for example, in 10% of the slider the circle 4 will have radius of 20px, circle 2 10px, circle 5 stays the same, etc...). As you may have already guessed, i will try to "transition" the resizing-repositioning smoothly when the slider is being moved.
The approach i have tried tried so far: instead of manually trying to position them i've tried to use a physics engine-
The idea:
place some kind of gravitational pull in the center of the screen
use a physics engine to take care of the balls collision
during the "drag the time" slider event i would just set different
ball sizes and let the engine take care of the rest
For this task i have used "box2Dweb". i placed a gravitational pull to the center of the screen, however, it took a really long time until the balls were placed in the center and they floated around. Then i put a small static piece of ball in the center so they would hit it and then stop. It looked like this:
The results were a bit better, but the circles still moved for some time before they went static. Even after playing around with variables like the ball friction and different gravitational pulls, the whole thing just floated around and felt very "wobbly", while i wanted the balls move only when i drag the time slider (when they change sizes). Plus, box2d doesn't allow to change the sizes of the objects and i would have to hack my way for a workaround.
So, the box2d approach made me realize that maybe to leave a physics engine to handle this isn't the best solution for the problem. Or maybe i have to include some other force i haven't thought of. I have found this similar question to mine on StackOverflow. However, the very important difference is that it just generates some n unspecific circles "at once" and doesn't allow for additional specific ball size and position manipulation.
I am really stuck now, does anyone have any ideas how to approach this problem?
update: it's been almost a year now and i totally forgot about this thread. what i did in the end is to stick to the physics model and reset forces/stop in almost idle conditions. the result can be seen here http://stateofwealth.net/
the triangles you see are inside those circles. the remaining lines are connected via "delaunay triangulation algorithm"
I recall seeing a d3.js demo that is very similar to what you're describing. It's written by Mike Bostock himself: http://bl.ocks.org/mbostock/1747543
It uses quadtrees for fast collision detection and uses a force based graph, which are both d3.js utilities.
In the tick function, you should be able to add a .attr("r", function(d) { return d.radius; }) which will update the radius each tick for when you change the nodes data. Just for starters you can set it to return random and the circles should jitter around like crazy.
(Not a comment because it wouldn't fit)
I'm impressed that you've brought in Box2D to help with the heavy-lifting, but it's true that unfortunately it is probably not well-suited to your requirements, as Box2D is at its best when you are after simulating rigid objects and their collision dynamics.
I think if you really consider what it is that you need, it isn't quite so much a rigid body dynamics problem at all. You actually want none of the complexity of box2d as all of your geometry consists of spheres (which I assure you are vastly simpler to model than arbitrary convex polygons, which is what IMO Box2D's complexity arises from), and like you mention, Box2D's inability to smoothly change the geometric parameters isn't helping as it will bog down the browser with unnecessary geometry allocations and deallocations and fail to apply any sort of smooth animation.
What you are probably looking for is an algorithm or method to evolve the positions of a set of coordinates (each with a radius that is also potentially changing) so that they stay separated by their radii and also minimize their distance to the center position. If this has to be smooth, you can't just apply the minimal solution every time, as you may get "warping" as the optimal configuration might shift dramatically at particular points along your slider's movement. Suffice it to say there is a lot of tweaking for you to do, but not really anything scarier than what one must contend with inside of Box2D.
How important is it that your circles do not overlap? I think you should just do a simple iterative "solver" that first tries to bring the circles toward their target (center of screen?), and then tries to separate them based on radii.
I believe if you try to come up with a simplified mathematical model for the motion that you want, it will be better than trying to get Box2D to do it. Box2D is magical, but it's only good at what it's good at.
At least for me, seems like the easiest solution is to first set up the circles in a cluster. So first set the largest circle in the center, put the second circle next to the first one. For the third one you can just put it next to the first circle, and then move it along the edge until it hits the second circle.
All the other circles can follow the same method: place it next to an arbitrary circle, and move it along the edge until it is touching, but not intersecting, another circle. Note that this won't make it the most efficient clustering, but it works. After that, when you expand, say, circle 1, you'd move all the adjacent circles outward, and shift them around to re-cluster.
I'm writing an JavaScript application that is drawing arbitrarily shaped objects on a HTML canvas. The user should be able to select any of the objects by clicking on them.
To make this an O(1) operation I'm using a shadow canvas, i.e. a not displayed canvas that has exactly the same size, where each object drawn on the normal canvas is also drawn there - but with a color that represents it's ID.
So a simple ghostContex.getImageData() together with the mouse click coordinates gives me the color at that pixel and thus the ID of the clicked object.
All of that is working fine - except when I click on the exact border of an object.
As it's drawn with anti-aliasing on the ghost canvas I get a wrong color (as that color is a mixture between the correct ID and the ID of the object under it that was drawn before...). This wrong color is representing a wrong ID and thus I'm selecting a totally different object :(
How can I solve that problem?
Note #1: I'm already using the translate(0.5, 0.5) trick to prevent most anti-aliasing
Note #2: I was trying to write this application with SVG before, but especially this object selection was extremely slow as I guess it's been too many objects for the collision detection. That's the main reason why I want a O(1) approach now... Oh, and this way I can easily draw a much bigger line on the ghost canvas than the line is drawn on the normal canvas to make picking much easier.
Note #3: Relevant browsers are Firefox, Chrome, Android 2.3+ native and iOS native
The reason why I couldn't accept any answer here is quite easy and quite sad: it doesn't exist... :(
The antialiasing can not be switched of, the standard has no method for that. But the standard does have a hit test function (http://www.w3.org/html/wg/drafts/2dcontext/html5_canvas_CR/#hit-regions) that would do exactly what is needed here. Even in a nice way that would hide the nasty details for the developer - but it's not implemented in any of the browsers right now.
And implementation was looking to be far away till impossible (see e.g. comment #6 at https://code.google.com/p/chromium/issues/detail?id=328961). But apparently it gained momentum during the last month...
So what can be done in the mean time? What did I do?
In my code I could implement for each shape a isPointInShape() method. So I use the ghost canvas trick to get a shape and verify with the isPointInShape() that I really selected the correct shape. This helps in the anti aliased pixels not to pick a wrong shape (just think of clicking on the border of shape #2 where we had a 50% antialias transparency - this would tell you wrongly a selection of shape #1...).
If implementing a generic isPointInShape() is quite hard for your shape you could try a trick that I was reading of somewhere else (I didn't try it tough, so I haven't tested it...):
Create an additional ghost canvas of size 1x1 pixel that is positioned exactly on the mouse position. Then draw the shape of interest - when the A of the RGBA is changed, this shape does belong to that pixel.
I know this is an old post, but recently I had a similar issue. The way I solved the "seam of two colors" problem was doing a 10x10 pixel sampling of the secondary canvas instead of a single pixel. I then stringified the RGB values and used these as keys in a map that mapped to the object that color represents. So initially with the 1 pixel sampling I used the map immediately to determine the associated object but antialiasing created halfway colors that didn't exist in the map. The 10x10 method solves this problem by looping through the 100 RGB values returned and creating a "counting map." This map uses the stringified colors and maps them to a count, but only includes valid colors from the first map in the count. So you end up with a map saying you counted 65 red pixels and 23 blue pixels (where the remaining 12 pixels were some weird anti-alias hybrid). In the same loop where I was counting the colors I also maintained a variable for current max count and current color associated with that max count (to avoid looping through this new map again). Now at the end you have the color that was counted the most in that 10x10 sampling and can use that to map back to the object associated with it. You will only get an undefined result if no valid colors were found in the 10x10 sample which you can reasonably assume means the "background" was clicked.
I made up the name ghost context! Are you using my old tutorial? :)
In that old tutorial I do not clear the ghost context after each object is drawn to it. In your case, to fix your issue, you may need to clear after testing each object on the ghost context.
Make sure of course that you are translating the ghost context and normal context by precisely the same amounts. (and translating them back, or resetting the transformation, afterwards).
I am rendering a map out of SVG paths (using jVectormap).
There are cases where one region has to be merged with the neighboring region.
Unfortunately both regions don't touch each other and I have to interpolate to fill the space in between.
jVectormap uses very simple SVG paths with M to set the the absolute startpoint and l to connect relative points.
Does any of the SVG libraries cover such an operation?
I haven't tried this, but you may get around it by running the converter at jVectormap with the following parameters:
--buffer_distance=0
--where="ISO='region_1' OR ISO='region_2'"
Where region_1 and region_2 are the two regions that you need to merge.
Solving the problem this way also means that the generated SVG paths are true to the original coordinates, whereas a following fix may lead to some (probably minor) inconsistencies.
This might not be the kind of answer you're looking for, but using Raphael.js you could loop over the entire length of the path of one region getPointAtLength(), comparing it with all points of the second region. If the coordinates are closer than n pixels from any coordinates on the second region and the previous coordinates weren't, than that could be regarded a "glue" point. You would then jump to the second regio and start looping over it, if the next point is still closer than n points, than go in the opposite direction, if still closer change direction and go farther along the path till finding a point that's farther away from the original region than n pixels. Continue looping in that direction till once again finding a new "glue" point, where once again you will switch to the original region in the manner described and all points which weren't covered in this final loop could be discarded (or you could simply create a new shape based on the points you came across whilst looping over the length of the original region.
True enough, it's not the easiest script to make, but it should be quite do-able I believe, especially when you can use a function like getPointAtLength to find the points between the defined svg points (though you need to only 'record' the defined points, and that's sort of the hard path as Raphael.js doesn't excitedly have any functions which would help with this, still even that shouldn't be too hard to match up by hand (in code of course)).