Monogame – Working with Touch

*NOTE – This may also work on other platforms with touch as well, but this hasn’t been tested on anything other than Android at the current moment.

One fundamental aspect to understand about touch and gestures is that code needs structured around the idea of continuous input. Thus, any touch recognition code should be encapsulated somewhere within the main game loop; where this is would be dependent upon how one elects to parse input. The reason for this is that the nature of all touch processing is a sequence of touch events that get fired in succession; there are only a few exceptions to this rule.

The other aspect to understand clearly is nomenclature mapping. What you think you want to achieve in your design may, unless you’re already familiar with either the Monogame or Xamarin frameworks, not necessarily be what either of those aforementioned frameworks are calling it through its API parlance. So be prepared to step outside your normal wheelhouse and, perhaps, discard some long-standing assertions about what truly a touch/gesture really is.

First, the consideration needs made as to if you’re going to handle touches or gestures – don’t get too caught up on thinking that a touch is a single press, because this will cause you some unnecessary grief later. If your program ebbs toward the former, there’s usually no requisite configuration needed, other than to check for the existence of a touch-capable input device and adjust your engine accordingly (the only other exception here would be if one wishes to perform touch-to-cursor mappings, but this is outside the immediate scope of this article). Conversely, gesture handling requires some configurations be made before they can be used, and this is where the Monogame documentation, as well as a majority of the information available on various forums, falls fatally short. We will focus on this once we start addressing gesture handling, which follows a look at touch handling.

Checking for the existence of hardware with touch capabilities can be queried through the TouchPanelCapabilities object, triaged through the TouchPanel static object as such:

TouchPanel.GetCapabilities ().IsConnected;

The IsConnected property is a boolean that indicates the presence of a touch-capable device. Obviously, the absence of one suggests either that the device is intermittently available, or that other sources of input are necessary. In this case, neither the touch nor gesture APIs would be valid.

Concerning touches, the current state of the touch panel holds a collection, called TouchCollection, of TouchLocation objects. Each of these correspond to a single touch event generated by the user when a press is determined to have occurred on the sensitive surface. It’s fair to suggest that multiple points of contact yield multiple TouchLocation instances within the TouchCollection (i.e. as a practical example, one finger would generate one instance, two fingers would generate two instances, etc. This can best be observed while debugging a program using this technique, and paying attention to the Id property of the TouchLocation instance(s).). In order to properly ascertain the most accurate state of the touch panel, we’ll need to do the following:

  1. Obtain the current state of the touch panel
  2. Determine if there are any TouchLocation instances in the TouchCollection collection
  3. If there are, take relative action based on any of the properties of the current TouchLocation instance

This can be accomplished using the following general template

TouchCollection tc = TouchPanel.GetState ();
foreach (TouchLocation tl in tc) {
 // Do something here
}

Fortunately, TouchLocation instances are very simple to use. There are only four properties that are of any practical significance, and one utility function for trying to determine the previous location (which, at least during my testing, wasn’t useful for anything). They are as follows:

  • Id – An Integer that uniquely identifies a single TouchLocation instance within a TouchCollection. It’s unknown how its potential values are determined, or if orphaned values are subject to recycling after the host TouchLocation has fallen out of scope.
  • Position – A Vector2 that provides the X and Y coordinate serving as the source for the event. Effectively, this is the location on the sensitive surface where contact was made.
  • Pressure – A floating-point number indicating the pressure of the touch. I’m unclear on how exactly this works, since my tests always reported a zero in this property. The only conclusions I can come up with here are either that my device doesn’t support touch sensitivity of this kind, or I missed a configuration step to enable this functionality.
  • State – An instance of TouchLocationState that determines what kind of touch we’re dealing with. This property can have one of four values:
    • Invalid – The press has been somehow deemed invalid; I’ve never seen this occur in testing, and am left to think that either I failed to satisfy conditions to make this occur, or that it’s simply a dump case for an exceptional condition.
    • Moved – Seen when a press has either remained in the same position or has moved. This is a very important state as it has a great deal of practical application, so do try to keep it in mind.
    • Pressed – Observed when a point of contact on the sensitive surface is newly minted. This is only fired once, and will not be seen again, regardless if the contact remains afterward. This could potentially be a source of confusion for a number of programmers.
    • Released – Likely the last state that a TouchLocation would be in before falling out of scope, it will be fired when the source of contact which generated this particular instance is no longer available.

Having said all of that, you now have enough information to properly utilise touches within your programs. As was stated before, simply ensure that your code is contained within the main game loop somewhere, since the data will likely change per frame, or at least as often as it can. An example of how to implement code based off this logic will be illustrated at the end of this discussion.

Gestures, insofar as Monogame is concerned, are a bit of a hassle to work with, mostly due to the lack of upstream documentation. We will seek to correct this imbalance, if not for the official documentation, then at least for programmers who wish to learn more about them.

As was stated previously, although Monogame performs a considerable amount of work to make available the touch and gesture API for programs deployed on capable hardware, gestures are left a bit open-ended by comparison to their touch counterparts. What this means is that as a programmer, you’re required to provide some configuration before the gesture API can be utilised. Here, we assume that you’re only interested in gestures, and not touch-to-cursor mappings, hence will only discuss the former.

Before proceeding, some basic information should be given as to the nature of gestures, and how they’re procedurally handled.

Although there is some very minor overlap with how a touch and gesture are expressed, they are two discrete entities. Gestures can be composed of one or more points of contact, and it’s expected that the locations of these contacts will change, in a particular way, over an indeterminate amount of time (ergonomic measurements would likely dispute this generalisation, but it is for this conversation a generalisation, and not a scientific claim). The ways in which these contacts change, or at least the resultant shape the change yields, as well as the number of contacts involved in the measurement, hints at the particular kind of gesture. In other words, a single point of contact that has a gradual change in its X-axis, be it positive or negative, which would yield a ray (or a series of small rays), is generally considered to be a horizontal drag gesture. When considering the same principles but looking to the Y-axis instead, we now find ourselves dealing with a vertical drag gesture. Pinch and zoom gestures typically involve two or more points of contact that move near concertedly away from or toward each other along the same logical axis. Perhaps paradoxically, at least when considering a contrast between touches and gestures, taps, double taps, and long-presses are registered as gestures as well; these are more concerned with the sustainment of a single point of contact relative to the time from when it was first recognised.

From a stock perspective, Monogame provides eleven types of gestures, referred to as GestureTypes. These types will effectively determine how gesture detection is performed (it’s unclear if the GestureType framework can be extended to facilitate custom gesture types, but this is a considerably advanced topic which will not be discussed here). However, Monogame will not automatically read the touch panel for gestural input. Instead, it needs instructed on which kinds of gestures to detect, and this is provided by the programmer. In any non-looping block of code, preferably during the initialisation routines, you’ll need to specify what are called EnabledGestures, which is a property of the TouchPanel static object. Multiple gestures can be configured by OR’ing one or more of the types together in the assignment statement. For example, if I wanted to parse for both a HorizontalDrag and a DragComplete gesture, I would write the following statement:

TouchPanel.EnabledGestures = GestureType.HorizontalDrag | GestureType.DragComplete;

Once this is complete, you’ll have done enough to get Monogame to start playing nice with at least these two kinds.

Parsing gestural input is, in essence, no different than parsing touch input, but there are some minor differences to the process. To start, we must first determine if there are any gestures with which to read data from. If we do not do this, attempts to read directly from the gesture store will generate fatal exceptions. Fortunately, the TouchPanel static object provides a boolean property called IsGestureAvailable, which will inform clients of the availability of queued gesture data. If we have data, we must convert the data into a sample, which is packaged into the GestureSample class. As with the TouchLocation object, the GestureSample object contains several properties that are of practical interest to the programmer, especially when making contextual decisions that respond to this kind of input. GestureSamples include the following properties:

  • Delta – A Vector2 instance which provides the delta, or difference, data for the first touch point in the gesture. This will change over time, and will always be relative to the coordinates where the touch was first recognised.
  • Position – A Vector2 instance which contains the current coordinates of the first touch point in the gesture.
  • Timestamp – A TimeSpan instance that indicates the time when the gesture was first recognised.
  • GestureType – A GestureType instance that indicates what type of gesture was determined based off several criteria.

Additionally, GestureSample contains properties called Delta2 and Position2, which are used to track a second point of contact that’s being measured as part of the current gesture. What this implies is that insofar as the stock gestures are concerned, Monogame will only be able to handle gestures where no more than two points of contact are involved.

My advice here is to experiment with the data through debugging until you’re comfortable with how these gestures are read, because there are some nuances with how the data continuously polls respective to different gesture kinds. For example, a HorizontalDrag gesture will, while the drag is occurring, constantly emit the HorizontalDrag signal until the contact source is released, terminating the gesture. At this point, if one is checking for the DragComplete signal as well, releasing the contact source will cause the touch panel to emit the DragComplete signal.

Examples:

To determine if a single press has been made:

TouchCollection tc = TouchPanel.GetState ();
foreach (TouchLocation tl in tc) {
 if (TouchLocationState.Pressed == tl.State) {
  // Execute your domain-specific code here
 }
}

To determine if a press was made, and has been held in the same position for an arbitrary period of time:

TouchCollection tc = TouchPanel.GetState ();
foreach (TouchLocation tl in tc) {
 if (TouchLocationState.Moved == tl.State) {
  // Execute your domain-specific code here
 }
}

To track the position of a horizontal drag:

(1) During game initialisation:

TouchPanel.EnabledGestures = GestureType.HorizontalDrag;

(2) During game loop:

while (TouchPanel.IsGestureAvailable) {
 GestureSample gs = TouchPanel.ReadGesture ();
 if (GestureType.HorizontalDrag == gs.GestureType) {
  // Execute your domain-specific code here
 }
}

Clicky Game – Development Journal 0001

Because I have no life, and because I really suck at having good ideas, the concept of Clicky Game was born.

Now ordinarily I wouldn’t bat two shits at this thing after having written something like that, but I wanted to use this as an opportunity to really dig deep back into C++ and use some of the features in C++11. I just want an excuse to use lambdas liberally. 🙂

I’m doing a few interesting things with this project. First of all, I’m writing it in Visual Studio. Yes, I know, blasphemy. The reason for this though is because my new job throws me into a DevOps-type position where I’m going to have to be writing code for integration into an ERP Package we use. Unfortunately they only provide an API in C# and since we’re a majority Microsoft Shop, I need a MSVS Primer. This would be it.

Sticking with the badassery that is MSVS, I’m trying out Team Foundation Server for VCS. This is drastically different from my traditional use of Git. So far, I hate it. It’s OVERKILL for a single dev such that it’s almost not quite suitable for a single dev. But we’re going to stick with it.

So far, I’ve had two solid days of coding (about 12 hours a day) and I’ve gotten into this interesting area where I’m very heavily extending the SFML Framework that I’m using for the major library. It’s actually a really good library. It’s just missing a lot of things that I need. For example, there is no native construct for handling 2D animation. I find this to be a little odd since it’s primarily a 2D library. But that’s sort of cool since it lets your roll your own implementation. It also doesn’t have any native constructs for UI. This leaves me in a bit of a predicament since there’s no real solid UI library that integrates with SFML (guichan is strictly for SDL/Allegro) so now my current task has been to create a bit of a library that does this.

Doing all of this seemingly extra work is actually pretty cool since I’m able to use modern coding features like named lambdas for event handling (by use of std::function wrapper for class member). As another challenge, all allocations are dynamic keeping as little overhead on the stack as possible. So far, this seems to have a tremendous performance benefit but, as you could imagine, it’s requiring A LOT of double checking for things like new/delete pairing, reference/dereference members for appropriate address/value access syntax, test assertions on members prior to use in expressions even in places where it may be safe to assume that the memory should be successfully allocated and the respective member instantiated, thread safety, cross-member asset access, etc… A lot of really interesting technical hurdles.

I think I’m going to do a little bit of a piece on this for the next installment of “Something with Greg” which is shaping up to be the programmer episode.

Development Journal – Teh Rawness

Lets face it, I’m not a professional developer nor a professional mathematician nor a professional anything. Maybe a professional jackass. Yeah I am pretty good at that.

Douchebagery aside, I managed to clobber together an extremely raw working model for a “Drop Objects”-style game for Android that is most definitely going to morph into something a fair bit cleaner and more disturbing. I peddled this off to my tight-knit inner circle of unlucky friends to see what they thought and I received a lot of constructive criticism (because it does suck and really it’s supposed to at this point) and some really cool ideas as to where this could possibly be taken.

If you have an Android device, you can side load (pay attention to steps number two and three) this on there and have at it. Yes, I’m ignoring continues for the time being.

Additionally, don’t bitch or moan at me because this doesn’t work on your shitbox Android device that still runs Gingerbread or some hack-fuck $20 tablet from the Himalayas. This isn’t even anything close to a complete idea but it is somewhat usable.

You can get the APK from my Google Drive here: http://goo.gl/UdTZDL

Development Journal – I Can Haz Procedurally Ramped Difficulty?

Preface – I’m not a mathematician in any way, shape or form.

Shamefully, one of the things that’s always bugged me about any game I’ve ever written was the difficulty was explicitly defined. In other words, I would always have a method that would check the current level and apply random scalars to settings depending upon that check. Does it work? Yes. Is it intuitive? No. Does this make for a horrible game experience? Yes and no (more yes).

Without diving too far into the rabbit hole, I wanted a way to automatically increase the difficulty of a game while still retaining certain qualities. Simply ramping the difficulty could be achieved in a number of ways depending on how you want the game to be. If you want it to react to how the player makes decisions in the game, well that’s a whole other issue that I’m not going to dive into right now as it could get complex really quick. For the project that I’m working on now, I wanted something a little more simple. Why not a logarithm?

Logarithmic graphs are really nice to look at but present some interesting hurdles that you need to compensate for in other ways.

First of all, I decided that I’d play with the natural logarithm instead of another base. I like smaller numbers as they’re always easier to manage (plus, I’m lazy). To entangle it a bit more with the game, I decided to take the natural logarithm of the value of the current level multiplied by two, squared. So it would look something like this:

ln((currentLevel*2)^2)

Java has a nice log method in Math that operates on the natural so the code actually looks something like this:

(float)Math.log((Math.pow(currentLevel * 2, 2)));

This little modification to the natural log gives a relatively nice curve.

Image

This is just a sample of what I was getting. But why use the current level multiplied by two then using the value of that number raised to the power of two? Because it produced the nicest results in all of the testing that I did plus it ties into the current level which helps to give the impression that the difficulty scales with the levels. Levels pushing into the mid to upper 90’s produce a value that’s 10.xx and quickly ramps up from there which can cause some problems in systemic calculations (since you’re actually using 1.x (1xx.xx%) as a multiplier which will always give you at least the number you’re multiplying against which is not desired in most cases). However this fact is taken into consideration and compensation is made for it where needed.

So what can you do with this value? Well, in the simplest terms, the possibilities are endless. And, frankly, you don’t even have to calculate it the same way I did. You can do whatever you want, so long as it makes some sense. But I chose to tie it to the level and amp it up a little (the base value returned from ln(level) was a little low, even for my tastes). The great thing about this seemingly insignificant number is that it can actually hold a lot of weight for procedurally generating difficulty scalars (which is basically what this is). Variations of this value (mostly being derived from rounding functions like floor or ceiling) can be used to help determine the total number of objects to work with in a level or how many enemies to pack into a wave. If the player has a goal that’s a fraction of a total number of objects, this value can be used to help determine that percentile and you can apply it there and elsewhere. You can also use it as an abstract base in probability calculations so that you can make things happen more slowly in early levels and more quickly in later levels, helping to increase that sense of difficulty.

Another thing to keep in mind that could potentially help is that an exponential curve is the inverse of a logarithmic curve. So if you find yourself in a position where you logically need to do things that go against the logarithmic curve but still need to retain that difficulty, having a second measurement from the exponential curve of the same method that calculates difficulty could be beneficial.

Game Development – Migrating to Classical Mechanics

Let’s clear up some possible confusion regarding the title of this post. I’m not necessarily directly talking about game play mechanics as I am talking about the branch of physics called Classical Mechanics. You know, the fun stuff that helps us describe motion of mass under certain types of forces and the effects, both direct and indirect, resulting.

Well it’s fun for me anyway. Even though I hadn’t necessarily realized how much I’d forgotten about really simple stuff.

And let’s clear one more thing up here. I’m not a professional mathematician or physicist. I’m a software engineer. So if you’re looking for a primer on those areas, you’d be better served by Wikipedia/Wolfram, sites dedicated to those areas, or proper coursework. More importantly, my understanding of certain concepts might not be as robust as a skilled professional in either of those areas but I’m confident enough that I can describe what I see in everyday life enough with classical mechanics to be proficient in what’s called applied mechanics (that was actually my strongest point).

What I wanted to talk about here is something that I’m sure every game developer has dealt with at some point in time when designing a 2D game (strictly 2D). But to best describe what I’m getting at, I should probably start with an example.

Moving a block from one point to another is a relatively simple task to accomplish. Assuming that you’re not using an origin offset of some type, moving from point A to point B would look like this:

A simple affine transformation
A simple affine transformation

Geometrically speaking, this can be accomplished by a simple affine transformation. However, even though you could get away with expressing this event with an affine transformation, it’s not taking into account how this would happen in the real world. Even autonomous movement doesn’t occur without some type of external force being applied to the object to make it move in a certain direction. That being said, an affine transformation like this wouldn’t actually happen without some force being applied to the rectangle to make it move from vector A to vector B. Visually, the player may or may not be able to tell the difference between which method you chose to use. But we all know which one is more fun. 🙂

With that example, I wanted to point out that even in the most seemingly simple situations, it’s really easy to avoid the use of classical mechanics. But should you even if you could?

The really nice thing about classical mechanics is that the rules for movement, collision, and forces are all already laid bare before you. Even better is that these rules and observations are and have been made about real-world objects and these rules can be expressed mathematically (thus you’re translation point into software). At that point, it’s nothing more than to write a utility class or a series of methods that parameterize those expressions and make arbitrary calls to them in code as needed.

Ignoring classical mechanics means that you’re basically left to invent your own set of rules for these behaviors. Not only would that mean that things would probably not do what a player would expect them to do, but it makes a significant amount of work for a developer.

One particular point of difficulty for developers looking to migrate to using classical mechanics would be the change in understanding of objects in the game world. You can no longer look at your objects and entities as mere rectangles and circles with dimensions based in pixels. Now you have to start thinking about how these objects relate to real-world counterparts. Gravity now comes into play thus properties like mass, density, volume, etc.. are all now factors. It’s not enough to simply say “the user pressed this key so now I call this method to do a transformation to make the player move from here to here”. Now it’s more or less along the lines of “the user pressed this key so based on the current factors like gravity, applied friction of the area they’re standing on, if the wind is blowing or not and how fast, how fast can they move in the direction requested and move them accordingly”.

It all comes with the territory transition though.

A really simple but fun exercise for this transition would be to try and write a Pong clone implementing as much of classical mechanics as possible. It’d be fun to discuss this so I think I might try to do so soon.