I'm trying to simulate a rope physically correct on a website.
Having searched the web, my conclusion is that I need a physics engine like box2d?
If I have understood it right the solution is to split up an object into small segments and then to join and animate these all together. In addition, I want to combine the physics with the browser. What that means is: when I'm scrolling the website fast down, the rope has to react in a physically correct manner.
is this possible?
You don't need a library at all.
You can happily do this with object, component or procedural code, and an understanding of basic mechanical physics and some 2D geometry (basic calculus might help).
Doing it in an optimized fashion would require more work.
Doing it in a modular and reusable fashion would require some upfront engineering.
But making a rope, and making the rope behave normally is quite straightforward.
A 2D rope would be a series of line-segments or "bones".
Each bone can bend around its joints.
You can apply gravity or whatever other forces you would like to each bone.
Each bone has constraints (the other bones it's attached to, above and below).
So as you update the "rope", you update each bone, based on the constraints which came before and after.
You can create an anchor point -- pinning the top of the rope to the wall, so that regardless of how the other bones move, the top-most bone will pivot around its top joint, but will not move anywhere.
To apply physics to the middle of the hanging rope (like pulling it by the middle, and then letting go), you would use Inverse Kinematics to solve how that force against one or two joints affected each of the other attached (and constrained) joints.
Think of it less like a snake, and more like a bike chain.
The shorter each "link" in the chain, the more fluid the rope will seem, but the longer it will take to process.
The longer each "link" in the chain, the faster you can compute the changes, but the more rigid and blocky it seems as it bends.
Look up "Verlet Integration", "Kinematics" ("Forward"/"Inverse") and have a half-decent grasp of the math behind rotation and moving an object along 2D vectors...
With a little bit of mass in there, if you want to get fancy with the whip-like stuff, rather than just making waves.
The rest is just loops.
See the following for a basic example:
http://gamedev.tutsplus.com/tutorials/implementation/simulate-fabric-and-ragdolls-with-simple-verlet-integration/
And have fun.
Related
I am using Matter.js physics in an attempt to create soft bodies. I was able to create a body like this:
However I am not sure if this is the "soft body" I want. It is true that this body is not entirely rigid and has that bouncy feel when it collides and gets dragged. I was looking for a body that shares similarities with a gelly. This image might visually help explaining the concept:
I was wondering how these type of bodies can be made. Is it the same as the as matter.js soft body but with a very specific type of properties? I can only get the body to be kind of rigid-squared and not as moldable and circular as I would like it to be.
I am also interesting in manipulating the physics body with in-game interactions which would increase or decrease the physics body size which leads me once more to the conclusion that the type of body that I want must be quite moldable.
Can matter.js handle this or do I have to change the physics engine? Any solutions to approach this?
NOTE: I am using Phaser.js for some in-game components but matter.js physics for physics manipulation because I believe Phaser integrated Physics can't simulate this type of complex body.
Thanks
EDIT: It is very similar to this Box2d :roll soft body ball. I just need to do that with a js engine I guess. Is there any?
As I mentioned in the comments, I am not familiar with phaser or how you would actually implement this within a Javascript framework. My goal here is maybe to give you some ideas on different ways to proceed, so hopefully you'll find this answer useful.
I will try to answer this:
I was wondering how these type of bodies can be made. ... I can only get the body to be kind of rigid-squared and not as moldable and circular as I would like it to be.
It is not necessarily clear what you want given this sentence. As I noted in comments, what I think you are looking for is plasticity, and I will describe a way which you could possible "cheat" that look with somewhat simple tools.
At the moment you describe the motion of your body by "It is true that this body is not entirely rigid and has that bouncy feel when it collides and gets dragged.". Currently your model works as such:
A point is connected to all other points as given in your mesh.
Every time step, a force is calculated between each pair. The total force on a joint (or point) is the sum of all these pair wise forces.
Each joint is associated with a part of the body (i.e. it has some mass m) and you calculate its acceleration with acceleration = force/m. From there on we calculate velocity and finally position.
The most interesting part of the steps above is nr 2, as that will greatly influence the motion of the whole body. A very common way to implement it is as an elastic potential that for a certain distance between two points gives some force. Like so:
function elasticPotential(p1, p2) {
// Given two positions p1 and p2 we calculate a force between them
distance = sqrt(pow(p1.x - p2.x, 2) + pow(p1.y - p2.y, 2) + pow(p1.z - p2.z, 2));
force = force_given_distance(distance); // A popular choice here is for example a spring force
return force;
}
Now, you already have the function described above built in in your framework, so you don't have to implement it. The reason I'm describing this is because it is essential to understanding how we can create plasticity. The problem with the above is that nothing will retain deformation---the nature of the elastic potential is that it has some rest configuration (most likely your first configuration) and it will always try to get back to that shape. We want the shape to remember how it was mis-shaped. This is what plasticity is.
Simple plasticity
Note first here that the problem of plasticity is a big research topic and in many cases far from trivial. My idea is as follows: if the distance between two connected points are larger than some threshold, remesh the points in the current configuration. That is,
for each pair(p1, p2):
if distance(p1, p2) > threshold:
recalculate_connection(p1, p2)
As you can see this is a very simple model for plasticity, and most likely not physically correct. However, it should be possible to get interesting behaviours my playing with the remeshing together with what elastic potential you choose.
If you provide me with more details I might be able to discuss the problem further, but right now I feel this answer is already longer than it should be.
TL;DR:
Create a "moldable" shape by remeshing your body during deformation. It might be tricky to get an exact desired physical behaviour, but it should be possible to create something that looks "gelly-like".
Sorry for my bad English.
I do a little game in JavaScript using Box2D (although I think the language is not important, because the engine is the same, as is well known, and has been exported to JavaScript).
Connecting several bodies via Distance Joint. When creating a joint pointing frequencyHz = 11 and dampingRatio = 0 (as I understand it, the less dampingRatio, the faster the item returns to its original position, that is, the spring will be tougher that I need). For each body to use force:
body.ApplyForce(new b2Vec2(0, 5800), body.GetWorldCenter())
That I needed to have these bodies was greater gravity than others.
After creating several elements, they begin to twitch, to vibrate as if they were something haunted, stop and engage in a certain position.
I tried to "play" with parameters frequencyHz and dampingRatio have joint, and sought to design not twitch, but then the construction seems less harsh and smoother.
There is some sort of solution?
Thanks.
I think that the structure is vibrating due to the fact that the weight of several elements, and the power applicable to them, the object is pulled down by increasing the length of the joint, the joint is aimed szhimatsya back to its original position, due to this vibration is obtained, because the element moves quickly in different directions
I'm trying to make a little platform game with pure HTML5 and JavaScript. No frameworks.
So in order to make my character jump on top of enemies and floors/walls etc., it needs some proper collision detection algorithms.
Since I'm not usually into doing this. I really have no clue on how to approach the problem.
Should I do a re-check in every frame (it runs in 30 FPS) for all obstacles in the Canvas and see if it collides with my player, or is there a better and faster way to do so?
I even thought of making dynamic maps. So the width, height, x- and y coordinates of the obstacle are stored in an object. Would that make it faster to check if it's colliding with the player?
1. Should I re-check in every frame (it runs on 30 FPS)?
Who says it runs in 30 FPS? I found no such thing in the HTML5 specification. Closest you'll get to have anything to say about the framerate at all is to programmatically call setInterval or the newish, more preferred, requestAnimationFrame function.
However, back to the story. You should always look for collisions as much as you can. Usually, writing games on other platforms where one have a greater ability to measure CPU load, this could be one of those things you might find favorable to scale back some if the CPU has a hard time to follow suit. In JavaScript though, you're out of luck trying to implement advanced solutions like this one.
I don't think there's a shortcut here. The computer has no way of knowing what collided, how, when- and where, if you don't make that computation yourself. And yes, this is usually, if not at all times even, done just before each new frame is painted.
2. A dynamic map?
If by "map" you mean an array-like object or multidimensional array that maps coordinates to objects, then the short answer has to be no. But please do have an array of all objects on the scene. The width, height and coordinates of the object should be stored in variables in the object. Leaking these things would quickly become a burden; rendering the code complex and introduce bugs (please see separation of concerns and cohesion).
Do note that I just said "array of all objects on the scene" =) There is a subtle but most important point in this quote:
Whenever you walk through objects to determine their position and whether they have collided with someone or not. Also have a look at your viewport boundaries and determine whether the object are still "on the scene" or not. For instance, if you have a space craft simulator of some kind and a star just passed the player's viewport from one side to the other and then of the screen, and there is no way for the star to return and become visible again, then there is no reason for the star to be left behind in the system any more. He should be deleted and removed. He should definitely not be stored in an array and become part of a future collision detection with the player's avatar! Such things could dramatically slow down your game.
Bonus: Collision quick tips
Divide the screen into parts. There is no reason for you to look for a collision between two objects if one of them are on left side of the screen, and the other one is on the right side. You could split up the screen into more logical units than just left and right too.
Always strive to have a cheap computation made first. We kind of already did that in the last tip. But even if you now know that two objects just might be in collision with each other, draw two logical squares around your objects. For instance, say you have two 2D airplanes, then there is no reason for you to first look if some part of their wings collide. Draw a square around each airplane, effectively capturing their largest width and their largest height. If these two squares do not overlap, then just like in the last tip, you know they cannot be in collision with each other. But, if your first-phase cheap computation hinted that they might be in collision, pass those two airplanes to another more expensive computation to really look into the matter a bit more.
I am still working on something i wanted to make lots of divs and make them act on physics. I will share somethings that weren't obvious to me at first.
Detect collisions in data first. I was reading the x and y of boxes on screen then checking against other divs. After a week it occurred to me how stupid this was. I mean first i would assign a new value to div, then read it from div. Accessing divs is expensive. Think dom as a rendering stage.
Use webworkers if possible easy.
Use canvas if possible.
And if possible make elements carry a list of elements they should be checked against for collision.(this would be helpful in only certain cases).
I learned that interactive collisions are way more expensive. Because you have to check for changes in environment while in normal interaction you simulate what is going to happen in future, and therefore your animation would be more fluid and more cpu available.
i made something very very early stage just for fun: http://www.lastnoob.com/
I've been trying to create something (much more basic) as in the video linked below:
http://blog.theclinic.eu/?p=653 (Should start at 14:30 ish)
It's a talk by John Maeda & he demonstrates his application called Powershop. I've been trying to recreate something that had the same effect, but I can't figure out how I could make the circles stay at a distance like that without collision, any suggestions on how to approach it?
I've tried to make the constraints have a min & max distance so that they'd follow around, I tried to let circles orbit, but none seems to look like his.
I'm trying this with javascript/ HTML5, but I would just like some tips or suggestions on the approach! (My physics/math knowledge is limited, so I might be missing out on some obvious concept to apply?)
Thanks in advance!
If you are looking for a nice canned solution, instead of building everything from the ground up, I suggest you look at Box2D.
The system you see in the Powershop graphics is a simple physical model where each "ball" or "node" or whathaveyou is a charged object that repels all the other balls/nodes. If you model the system as a collection of points connected by freely-rotating lines, all you have to do is understand a little physics to get this effect working with Box2D. Namely, like charges repel.
It should be that easy. You will constrain a set of points so that each has to stay within a length L from a center, and this will be your model of the arms all the balls rotate on. Then you will give each point the exact same charge and they will repel each other and spread out evenly with nice bouncy effects.
(The part where you get creative is how you want to add a whole new collection of points, like when the speaker in your Powershop talk clicks on a node.)
Intent on creating a canvas-based game in javascript I stand before a choice:
Should I performance-wise keep all the stuff happening in the screen in one canvas (all the moving characters, sprites) and redraw it at constant rate of, say, 60 FPS or should I break the scene into several smaller canvases thus removing the need of redundant redrawing of the scene? I could even create separate canvas elements for the characters' limbs and then do most of the animation by simply manipulating the CSS of the given canvas element (rotation, positioning, opacity).
To me the latter sounds way more plausible and easier to implement, but is it also faster? Also, shouldn't I perhaps use SVG, keep the characters and sprites as elements inside of it and manipulate their XML and CSS properties directly?
So what do you think is the most fitting solution to a scene with severals sprites and characters:
One canvas object redrawn manually (and wastefully) at FPS rate
Several canvas elements, redrawn manually in a more reasonable fashion
Structured vector graphics document like SVG / VML manipulated via DOM
I am mainly concerned about the performance differences, but the legibility of the logical code behind is also of interest (I, having already worked with canvas before, am for example fairly sure that the redrawing function for the entire canvas would be one hard-to-maintain beast of a script).
DOM manipulations are slow in comparison to GPU-accelerated canvas operations, so I would stay away from SVG and VML.
As far as structuring your canvas code goes, it certainly doesn't make sense (especially for performance reasons) to clear and re-draw the entire canvas because the player moved or performed an action. Based on your description here, I'm guessing that your game will be 2D. These types of games lend themselves extremely well to layering unless you're doing something rather complex like Paper Mario. You should be looking at the issue from an object-oriented viewpoint and encapsulating your drawing procedures and objects together as appropriate.
For instance, create a player object that maintains a small canvas representing the character. All the logic needed to maintain the character's state is kept within the object and any changes made to it need not worry about other components of the game's visual representation. Likewise, do the same for the background, user interface, and anything else you can abstract into a layer (within reason). For example, if you're doing a parallax game, you might have a foreground, background, character, and user interface layer.
Ultimately you will need to maintain the state of the different components in your game individually. Player animations, background clouds moving, trees swaying, etc. will all be managed by appropriate objects. Since you will already have that type of code structure setup, it makes sense to just maintain major components on separate canvas elements and composite them together as needed for better performance. If the character moves in the bottom left corner of a scene with a static background, you don't need to re-draw the top right corner (or 95% of the scene, for that matter). If you're considering full-screen capabilities, this is definitely a performance concern.
There's a rule in programming, that you should never try and optimize something before you have a speed problem with it. You'll spend more time trying to figure out how to code something in the best way than to actually code, and will never finish anything.
Draw them all on your canvas at a fixed rate. That's how it's done. If you start creating a canvas for each limb and element and manipulate them using CSS, you're wasting the potential of canvas. Might as well just use images. That's how they did it before canvas. That's the problem canvas was made to solve.
If you ever encounter speed issues, then you can start hammering at them. Check out these slides for some tips (related video). This guy's blog also has some handy tips on canvas performance.