Frogatto & Friends

Frogatto sprite

Frogatto & Friends is an action-adventure platformer game, starring a certain quixotic frog.
We're an open-source community project, and welcome contributions!
We also have a very flexible editor and engine you can use to make your own creations.

Featured on Apple’s Mac Software Games Page

July 28th, 2010 by Jetrel

And moreover, they’ve been doing that for the past 2 weeks.

Seen at

In fact, holy smokes, it’s even on 😮

If anyone involved in making that happen is reading this – THANK YOU! You guys kick ass!


Frogatto Available on the iPhone App Store

July 22nd, 2010 by Sirp

Frogatto has been released on the iPhone App Store!! Please show your support for our project by purchasing it.

We’re having an introductory sale with 60% off the planned regular price, so get in fast!


How Frogatto Formula Language (FFL) Works

July 18th, 2010 by Sirp

In Frogatto, we use Frogatto Markup Language (FML) to describe most game data — how levels are laid out, rules for laying out tiles, for defining animations for objects and so forth. For those of you familiar with Wesnoth and WML — or those familiar with XML — FML will seem very familiar. It’s a simple data language, like XML. Here is a small snippet of FML which defines one of Frogatto’s animations, to show you what I mean:


FML, like WML, works very nicely for describing data. However, in Frogatto we really wanted objects to have very flexible behavior — for instance, consider all the complexities of an object as simple as an ant in Frogatto. It has to walk back and forth, fall off cliffs for a red ant, but turn back for a black ant. Then when it is spat out it has to fly through the air, bounce off surfaces, finally ending up on its back and then spring back onto its front.

Describing behavior like this in FML would be far too awkward, at least without hard wiring a lot of core behavior into the engine, and we really wanted Frogatto’s engine to be a very general engine.

So, in addition to FML, Frogatto has an embedded language called Frogatto Formula Language (FFL). FFL is designed to work like a mathematical formula. That is, a formula has inputs, makes calculations, and then results in outputs. A formula itself can’t actually do anything — that is, it can’t modify the environment around it — it can only return a result. Just like a mathematical formula.

Let’s jump into an example of how this works in Frogatto. You know those big metal balls that are thrown by the psychotic bunnies? Here is a (slightly simplified) code snippet which controls what happens when they collide with a wall:

on_collide="set(velocity_x, -velocity_x/2)"

This is taken from the metal_ball.cfg file which defines the metal balls. Now, the first thing I want to note is that the on_collide=”…” part that surrounds this is FML. ONLY the part that is inside the quotation marks is a formula; a formula written in FFL. This defines the event handler that is run whenever the object receives a “collide” event.

What the formula is designed to do is cause the ball to be reflected off the wall, but its velocity dampened by half. One important thing to understand is that the formula itself does not modify the object’s velocity: a formula itself cannot modify its environment. Rather, the formula is evaluated and returns a command object. The game engine executes the command that the formula returns. In technical terms, this makes FFL a pure functional language.

There is an entire API of functions that are exposed to the formula system that will create different commands to return to the engine. The set() function, which creates a command to set the value of an object property, is probably the most useful, however there are a whole host of functions such as spawn(), which spawns a new object (useful, for instance, for an object which shoots projectiles), a teleport() function which allows teleporting the player to a different level, and so forth. The game engine actually comes with a utility that outputs all of the available functions.

Of course, in addition to functions that can create commands, to do useful things we need to be able to inspect the state of the game. For instance, in the above formula we had to read the object’s “velocity_x” property to find its horizontal velocity. When an event handling formula is executed, it gains access to all of the properties of the object receiving the event. Objects are pretty complex entities, and they have properties ranging from their velocity and location, to their hitpoints, current animation, a store of user-defined variables, the level they are located in — from where you can access all the other objects in the level — and so forth. Fortunately we have documented all the available object properties.

Now that we’ve seen the basics of formulas, let’s look at a slightly more complex example. This is how the Frogatto object handles collision with a wall:

on_collide="[set(velocity_x, 0),
if((animation in ['jump', 'fall']) and can_slide(self) and abs(velocity_x) > 200,
[animation('slide'), set(velocity_y, 0)])]"

First things first: this formula returns a list of commands to execute rather than a single command. Lists in FFL are delimited by [ and ]. The first thing this formula does is simply sets Frogatto’s horizontal velocity to 0 when he collides with a wall — if you run into a wall with Frogatto he simply stops rather than bouncing off.

The second part of the formula is to handle Frogatto’s ability to grab onto walls if you jump into them. It makes use of the if() function which is a built-in FFL function. if(cond, x, y) will evaluate to x if cond is true, and y otherwise. You can also use simply if(cond, x) which results to null if cond is false.

We can see that Frogatto will only cling onto a wall under certain conditions — if he’s in a jumping or falling animation, if a custom function defined as “can_slide” is true, and if his horizontal velocity has a magnitude greater than 200. If the criteria to cling onto the wall is met, we will return a command for him to enter his slide animation, and a command to set his vertical velocity to 0.

As we can see, FFL is fairly powerful, but hopefully not too difficult to understand. Using it, we can define objects which have all kinds of sophisticated behavior. Of course, another key element is understanding what events are triggered on an object. We have events that are triggered automatically, periodically, events that are triggered upon collisions of different types, events triggered when the level is loaded, when the player first approaches an object, and so forth. All the events are documented here.

I’ll give one more example of the kinds of things FFL can do:

on_timer="[set(brightness, brightness*4), schedule(5, set(brightness, brightness))]"

This makes it so a ‘timer’ event is received by the object every second. (Frogatto runs at 50FPS). On this timer event, the object is made to be four times as bright as normal for a tenth of a second (five cycles). Note that use of the schedule() function. What schedule does is takes commands and schedules them to be run some number of cycles in the future, rather than right now. So, we are setting brightness to 4x what is it now, and then scheduling it to be set back to its current value 5 cycles in the future.

Note how the entire formula is evaluated, and THEN the commands are evaluated.

FFL is a general formula language, and though its main use in Frogatto is for object events, that’s not its only use. It is also used, for instance, to draw the HUD which shows Frogatto’s status, health, coins, score, and so on. In that context, FFL is still used but it has access to a different set of properties and a different API — an API designed for drawing elements of the screen rather than controlling objects. It’s also used to allow custom scripts that can be used in the Frogatto editor. One can write a script in FFL that applies some effect or another on a level — such as rounding out a cave level, or adding trees to a grassy level. One could even write FFL to try to make an automatic level generator!

I’m hoping this gives a good overall view of FFL, and what it can do. The Frogatto engine is very moddable, and we’re hoping people will try to develop their own concepts — from fixing bugs in Frogatto, to adding new features, such as new objects or better behavior of existing objects. But one could also implement a completely new and different game. We very much welcome people trying to develop their own game concepts with FFL — if you do please come and share them with us on the forum. Good exercises would be to implement a game in the vein of Pong or Space Invaders of Pac Man.


Frogatto 1.0 Released!

July 13th, 2010 by Sirp

Frogatto 1.0 has been released! Frogatto is now a fully playable, fun, classic adventure platformer with over thirty levels, version 1.0 representing the first stable version of the game. Available for Windows, Mac, and in source form on our download page. Frogatto is also soon to be released on the iPhone App Store.

Frogatto also contains a fully functional editor that allows you to create your own fun levels or edit existing levels. The engine is heavily moddable, and as an Open Source game we welcome new talented contributors.

After trying Frogatto, consider visiting our forum to discuss the game.


Forum and Banners

July 11th, 2010 by Jetrel

We’ve made a few banners people can put in forum sigs and such. Feel free to link to them, just point them back here. In most forum software, this would get done by typing:

[url=][img] (the image address) [/img][/url]

And you can get that address by right-clicking on the image, and selecting something like “Copy image address” in the menu that comes up.

We also have a snazzy new forum set up, which is woefully empty at the moment. I’m sure you know how to fix that. 😉 The link to the forum is over on our left.

Besides that, I encourage you to read the post just below this and test our release candidate.


1.0 Release Candidate 1 is out

July 10th, 2010 by Ben

At long last (over 2 years), our first release candidate is up! 1.0 isn’t here quite yet, but, unless major bugs are found, it will be very soon. There are still minor bugs, and things that we’d like to do better, and many more features we’d like to add… but 1.0 is more of a beginning than an end, and we intend to keep improving the game a lot once it’s out.

So please, if you have some time, play through the game and let us know if you find any major problems!


Logo Update

July 8th, 2010 by Jetrel

We try to put the horse before the cart, here, so one of the last things we’ve bothered to put effort into is our logo, since without a good game to slap it on, a fancy logo isn’t worth anything.

I’ve made a new logo for frogatto (hand-pixeled, drew the letterforms from scratch). I think it’s about the same level of charm as the previous logo we had before, but is a lot more readable. In the attached image, you can see the progression from old-> new. The website will be updated shortly to reflect this.