There is a note on the cytoscape.js website that says:
"Note that a collection is immutible by default, meaning that the set of elements within a collection can not be changed. The API returns a new collection with different elements when necessary, instead of mutating the existing collection. This allows the developer to safely use set theory operations on collections, use collections functionally, and so on."
Does this mean it is not really suitable to use in the creation of online 'network editor' ie. where the user can interact to add and delete nodes and edges to the existing graph?
If I understand the note above it would mean that adding a new node would mean reconstructing the whole graph from scratch (but with the new node) and then presumably performing a complete redraw. Is this correct?
A collection is a set of elements; the set merely points to all the individual elements. You can think of it like an array of elements: The array just holds the elements. Different arrays/sets can have different, similar, overlapping elements, etc.
Cytoscape.js is very suitable for the purpose you mention. There are already projects that have live, collaborative editors (similar to google docs, online office, etc but for graphs). For example, a simple one that I created is codenamed "Factoid" for biological processes. Though I really think it ought to have a better, more accurate name -- you can still look through the code for a live collaboration example with Cytoscape.js. Because you can listen to events easily, it's relatively straightforward to send diffs (or even just events) back and forth between the server and the client.
Adding an element is inexpensive: It just adds the single element and redraws if opportune. It's even cheaper with cy.batch() for modifying lots of elements in a row.
Related
I'm trying to understand ECS. So a component is just plain data, and some manager holds these components in a container and loops through all of them to act on this data, to "update" them.
Is this manager what people call "component-manager" or is it a "system"? Or do they mean the same thing? If not, what does a component-manager and a system do?
ECS means different things to different people. There are a large number of approaches when it comes to implementation but I personally go by the following rules:
A Component is just plain data, typically a structure or some object with no logic associated with it what so ever.
An Entity is a collection of components. It is defined by an identifier, typically an integer, that can be used to look up components like an index.
A System is where all the game logic lives. Each System has an archetype, that is a specific set of components that it operates on. Systems have an update function, which when invoked accesses the specific set of components its interested in (its archetype), for all entities that have that specific collection of components. This update function is triggered externally (by what? see the next paragraph).
Now, here's the bit that addresses your question directly (or at least attempts to). Video games are simulations and they are typically driven by whats called an update loop (typically sync-ed to a monitor's refresh rate). In ECS architecture, there is typically dedicated code that strings your systems together in a queue and on each time-step of the update loop executes those systems in sequence (ie. calls their update functions). That bit of dedicated code not only manages the system update loop but is also responsible for managing components (stored as lists/arrays that can be indexed by an entity id) and a myriad of other tasks. In many implementations its referred to as the "Engine". This is what I take to be a "component-manager". But that could mean something else in another ECS approach. Just my two-cents. Hope it helped.
It's more of a software design question, than strictly programming, so I'll paste UML diagrams instead of code for everyone's convenience.
Language is Java, so variables are implied references.
I'm writing an app, that helps edit a very simple data structure, that looks like this:
On my first trial run I've included all the drawing-related and optimization code into the data structure, that is, every Node knew how to draw itself and kept a reference to one of shared cached bitmaps. UML:
It was easy to add (fetch a corresponding bitmap and you're done) and remove (paint background color over previously mentioned bitmap). Performance-wise it was nice, but code-wise it was messy.
So on the next iteration I decided to split things, but I may have went to far and things got messy yet again:
Here data structure and its logic is completely separated, which is nice. I can easily load it from file or manipulate in some way before it needs to be drawn, but when it comes to drawing things get uncomfortable.
The classic way would be to change data then call invalidate() on drawing wrapper,but that's inefficient for many small changes. So to, say, delete 1 Tile Id have to either have Drawn representation be independent of Data and call deketeTile() for both separately, or funnel all commands to Data through Drawing class. Things get even messier when I try to add different drawing methods via Strategy pattern or somehow else. The horror:
What wis a clean efficient way to organize interactions with Model and View?
First, definitely decouple the app logic from UI. Make some model for your schematic. That will solve your trouble to unit test the app model, as you already said. Then I would try the Observer pattern. But given that a schematic can have lots and lots of graphical components (your Tiles), I would change the usual setup for notifying every observer when something changes in the model, to notifying only the corresponding GraphicalComponent (Tile), when a Component gets changed in the Model. Your UI asks Model to do things, and gets called back in some parts to update. This will be automatic, no duplicated calls, just the initial observer registry on GraphicalComponent creation.
I have been trying to wrap my head around how ECS works when there are components which are shared or dependent. I've read numerous articles on ECS and can't seem to find a definitive answer to this.
Assume the following scenario:
I have an entity which has a ModelComponent (or MeshComponent), a PositionComponent and a ParticlesComponent (or EmitterComponent).
The ModelRenderSystem needs both the ModelComponent and the PositionComponent.
The ParticleRenderSystem needs ParticlesComponent and the PositionComponent.
In the ModelRenderSystem, for cache efficiency / locality, I would like run through all the ModelComponents which are in a compact array and render them, however for each model I need to pull the PositionComponent. I haven't even started thinking about how to deal with the textures, shaders etc for each model (which will definitely blow the cache).
A similar issue with the ParticleRenderSystem.. I need both the ParticlesComponent as well as the PositionComponent, and I want to be able to run through all ParticlesComponents in a cache efficient / friendly manner.
I considered having ModelComponent and ParticlesComponent each having their own position, but they will need to be synched every time the models position changes (imagine a particle effect on a character). This adds another entity or component which needs to track and synch components or values (and potentially negates any cache efficiency).
How does everyone else handle these kinds of dependency issues?
One way to reduce the complexity could be to invert flow of data.
Consider that your ModelRenderSystem has a listener callback that allows the entity framework to inform it that an entity has been added to the simulation that contains both a position and model component. During this callback, the system could register a callback on the position component or the system that owns that component allowing the ModelRenderSystem to be informed when that position object changes.
As the change events from the position changes come in, the ModelRenderSystem can queue up a list of modifications it must replicate during its update phase and then during update, its really a simple lookup each modifications model and set the position to the value in the event.
The benefit is that per frame, you're only ever replicating position changes that actually changed during the frame and you minimize lookups needed to replicate the data. While the update of the position propagates to various systems of interest may not be as cache friendly, the gains you observe otherwise out weigh that.
Lastly, don't forget that systems do not necessarily need to iterate over the components proper. The components in your entity system exist to allow you to toggle plug-able behavior easily. The systems can always manage a more cache friendly data structure and using the above callback approach, allows you to do that and manage data replication super easily with minimal coupling.
tiles:insertDefinition and tiles:insertTemplate both has putAttribute , i am not understanding the difference between the two.I am using tiles 2.x version.
thanks in advance
kranthi
A template is a view which expects to be supplied attributes while definitions are named instances of a template defined in tiles.xml (or pragmatically using the API).
tiles:insertDefinition requires the name attribue to be set, because you are inserting a defintion you have layed out in tiles.xml.
tiles:insertTemplate creates a new definition on the spot, from a view and expects you to insert values at that point. It requires the template parameter be set, there is no name attribute.
In general I don't think you should need to use either of these tags often (you can create tiles using applications without ever using either). Avoiding their use means having all definitions clearly laid out one place AND being able to see how all definitions fit together.
This central view is tiles greatest strength which these tags can undermine.
tiles:insertDefinition still means using named definitions, there is still one central location were all layout is controlled but because we are inserting the definition within a view we loose our overview of how everything fits together.
tiles:insertTemplate is akin to a JSP include, you are creating a new definition at that moment in the view and use it. This tile is not part of the overarching view.
In case the argument was not clear, JSP includes can achieve the same reduction in boiler plate code as Tiles can. It is the overarching view which tiles provides that allow you to easily change page structure across the whole application easily. Carefully consider that this is not being undermined.
I'm building an API and I have a question about how to represent objects.
Imagine we have a system with Articles that have a bunch of properties. Some of these properties are complex, for example the Author of the Article refers to another object. We have an URL to fetch all the articles in the system, and another URL to fetch a particular Article.
My first approach to implement this would be to create two representations of the same object Article, because when you request all the articles, it makes sense that you don't retrieve all the information about the Articles, but for example just the title, the date and the name of the author (instead of the whole Author object), excluding other properties like tags, or the content. The idea beneath this is to try to make the response of all the Articles a little bit lighter.
Now I'm going to the client side, and I decide to implement a SDK for Android, for example. So the first step would be to create the objects to store the information that I retrieve from the API. Now a problem pops up, because I want to define the Article object, but I would need two versions of it and it's not only more difficult to implement, but it's going to be more difficult to use.
So my question is, when defining an API, is it a good practice to have multiple versions of the same object (maybe a light one, and a full one) to save some bandwidth when sending the result of a request but generating a more difficult to use service, or it's not worth it and you should retrieve always the same version of the object, generating heavier responses but making the service easier to use?
I work at a company that deals with Articles as well and we also have a REST API to expose the data.
I think you're on the right track, but I'll even take it one step further. These are the potential three calls for large entities in an API:
Index. For the articles, this would be something like /articles. It just returns a list of article ids. You can add parameters to filter, sort, etc. It's very lightweight and I've found it to be very useful.
Header/Mini/Light version. These are only the crucial fields that you think will meet the widest variety of use cases. For us, we have a lot of use cases where we might want to display the top 5 articles, and in those cases, only title, author and maybe publication date. Those fields belong in a "header" article, or a "light" article. This is especially useful for AJAX calls as you don't want to return the entire article (for us the object is quite large.)
Full version. This is the full article. All the text/paragraphs/image references - everything. It's a heavy call to make, but you will be guaranteed to get whatever is available.
Then it just takes discipline to leave the objects the way they are. Ideally users are able to get the version described in (2) to save time over the wire, but if they have to, they go with (3).
I've considered having a dynamic way to return only fields people are interested in, but it would be a lot of implementation. Basically the idea was to let the user go to /article and then show them a sample JSON result. Then the user could click on the fields they wanted returned and get a token. Then they'd pass the token as a parameter to the API and the API would then know which fields to return.
Creates a dynamic schema. Lots of work and I never got around to it, but you can see that if you want to be creative, you can.
Consider whether your data (for one API client) is changing a lot or not. If it's possible to cache data on the client, that'll improve performance by not contacting the API as much. Otherwise I think it's a good idea to have a light-weight and full-scale object type (or more like two views of the same object type).
In the client you should implement it as one object type (to keep it DRY; Don't Repeat Yourself) with all the properties. When fetching a light-weight object, you only store a few of the properties, the rest being null (or similar “undefined” value for the given property type). It should be possible to determine whether all or only a partial subset of the properties are loaded.
When making API requests in the client on a given model (ie. authors) you should be explicit about whether the light-weight or full-scale object is needed and whether cached data is acceptable. This makes it possible to control the data in the UI layer. For example a list of authors might only need to display a name and a number of articles connected with that author. When displaying the author screen, more properties are needed. Also, if using cached data, you should provide a way for the user to refresh it.
When the app works you can start to implement optimizations like: Don't fetch light-weight data if full-scala data is already known & Don't fetch data at all if a recent cache copy exists. I think the best is to look at the actual use cases and improve performance with the highest value for the user.