# mike3

Member Since 06 Feb 2012
Offline Last Active Feb 13 2016 07:45 AM

### Cell based game and collisions in discrete space

03 January 2016 - 10:55 PM

Hi.

I am wondering about this. I was not satisfied with my previous system for doing this, which seemed kind of ugly or limited, and I was wondering what would be the most efficient and elegant solution.

What I have is a cell-based, turn-based game with a discrete game world, that is, it's a raster of tiles, not a space with (approximately) continuous (floating point) coordinates, with each object in one time. And I was wondering how you deal with collisions. In particular, each object can move but it can, obviously, only move from tile to tile, never be in between two tiles.

This means that when we get collisions, we have a number of cases to consider, and I'd preferably like something better than a casewise approach. Moving one cell at a time, we could have, e.g. that two objects move at each other, their coordinates would change by 1 cell each in opposing directions, causing them to swap places if they were right next to each other. They'd go through each other, so that should be a collision. Another way a collision can occur is that two objects try to rush each other for the same cell. A situation that might look like it would be a collision, but isn't, is two objects moving in the same direction, in the same line, one just behind the other. If you look at only the one in behind, one could think it will collide with the one ahead unless you also look to see which way that is moving, which adds more complicated, tricky programming to make it work on a computer. Things are further complicated by that some objects may move different velocities, crossing multiple squares in a turn (like a shot arrow).

Almost all the collision-handling stuff I've seen deals with continuous space and (approximate) continuous time, e.g. checking overlap, etc. and so does not seem obvious how to apply to a discrete space and maybe also discrete time.

One way I thought to handle it would be to just use a continuous simulation space which is "rounded" to discrete, but then we get a computationally-intensive simulation, as it seems that given the discrete character of the world space, we should be able to simplify/optimize things considerably.

What do you do?

### Programming "Widgets": how do you efficiently draw/redraw windows and widgets?

21 December 2015 - 10:02 PM

Hi.

I am wondering about this. I am curious as to how you efficiently program a "widget" GUI system, that is, a part of a program that draws interface windows with buttons and scrollbars and that type of stuff (widgets) on them.

I have done this a couple times before but I was not really satisfied with my previous attempts and am now curious about how you really make it efficient and clean. In particular, what I have is this: I represent the windows and widgets by a tree structure, which is "natural" because it has a natural hierarchical structure, in which the root node represents the whole screen, and then below that we have nodes for the windows, then each window node has nodes for the widgets, then each widget node has nodes for the components of the widget (It could go further, in theory, but this is as far as I go). The order in which the widgets/windows overlap (from front to back) is determined by the ordering of them as siblings on the tree -- the nodes keep pointers to the next sibling in a linked list.

The trouble is that I am trying to figure out how to make the render/drawing as quick and efficient as possible -- in particular, we may know that only certain widgets or components need to be redrawn, so we shouldn't need to explore every node of the tree, but we also have to deal with resolving overlap: we shouldn't redraw something with a higher position on the order if it doesn't actually overlap anything, but we also may not want to keep exploring the whole structure to check for overlaps every time we do a redraw. How can we efficiently do this whole process, including the overlap resolution, the latter ideally without having to check every sibling?

This has to have an already-existing solution since window-based GUIs are so ubiquitous. I am just not sure where to find a good description of it. What would that be?

### Messages and dynamic memory

20 December 2015 - 01:55 AM

Hi.

I am wondering about this. Is there a good way to do event messages between two large-scale loose-coupled parts of a game program without having to dynamically allocate and deallocate the messages? Messages may need to be queued, and there can be different types of messages, which suggests an inheritance hierarchy and that's where the dynamic memory stuff comes from, at least when using C++ as I'd be in this case. Thanks.

### Question about entity-component-system implementation for doors

14 June 2015 - 06:15 PM

Hi.

I was building a game program that uses an "Entity-Component-System" type architecture and was wondering how you would go about implementing doors. In the program as it stands, there are the following requirements:

1. Components should be generic enough that you can form new entity types without a type of component for every type of entity (as that essentially defeats the purpose of the ECS architecture, which is to allow you to make all kinds of things with composition),

2. Components should contain only data, no code.

3. Systems contain all the code for the logic.

4. There is a messaging pipeline where the systems can send messages to each other.

Given this, I am wondering how you would go about implementing doors? It seems that doors require a state and changing that state changes the graphic displayed for the door. Right now, I have a GraphicComponent which stores a key to a graphical asset, and a PositionComponent to store the entity's position. There's also a PhysicsComponent which stores the physical properties of the entity. But if I add a StateComponent to store the door's state, then, when you change states, that has to update the GraphicComponent somehow, and also the PhysicsComponent to make the door passable -- this is a tile-based game, not one taking place in a continuous space. However, because of requirement 1, genericity, we cannot have anything too specific to the door in the StateComponent, but we must specify how to update the other components. But how do we do that without violating requirement 2 -- absence of code in the components? I have a "Finite State Machine" (FSM) object in my program, which would seem to be what I'd want to use, however it's meant to be general (I use it in the user interface to handle various user interface states, such as main menu, playing the game, etc.) so when you make one you specify code, not just data. It would seem it would violate requirement 2 to stick that in the StateComponent.

What is a good way to do this? Should I just use the FSM and see if I can get away with it?

And it gets worse: what happens if you want to have the door be jammed by something else sitting on the door's tile when it's open? Then there needs to be something to sense the object is present. How can you do this without a dedicated system for doors which would violate condition 1?

### Map "areas"

31 August 2013 - 06:32 PM

Hi.

Suppose one has a 2D grid map for a game, and one wants to define special "areas" on the map, which could be bounded by a rectangle, ball, or polygon, and to which could be associated an effect or a name or something. I suppose one could store a list of these along with the level map, but what's the most efficient way then to find, given the player's position, which area(s) the player is in? How is this usually handled in games? Is the check performed every time the player moves?