Juice and Feel

Juice, or game feel, is the science and art of making pushing a button viscerally satisfying. Well, more precisely it's about giving feedback to confirm the player's actions. For games where flow and feeling matter, juice is the thing that makes the player understand your game without reading dials and processing numbers. Juice gives a game life and soul that makes the player feel like a part of the world. Juice is what makes a game feel fun without actually making any mechanical difference. And juice might just be what makes or breaks your game.

Whenever you do something in real life you get a wide range of sensory input in return indicating that what you tried to do actually happened. That response grounds you and makes you realise the reality and weight of things. As you might guess, replicating that kind of feedback on a flatscreen is hard. To get anywhere near reality you need hyperreal effects and nerve-blasting feedback to fill in for all the missing senses, all the while walking the fine line of overloading your player and making a dry, unresponsive world.

Of course, not all games need equal amounts of juice. Some games are played mostly in your head, and therefore all that visual feedback is not needed. Civilization has little more than flavour animations when a unit attacks, a town is built or a nuke blows up (actually the last one is pretty nice, but the real juice is your enemy’s tears). These are rather abstract both mechanically and visually, rarely pertaining to situations and perspectives we encounter in our everyday life. These games would still work with nothing but coloured circles and lines, because the strategy and the story exists in the player’s head. These games are planning games, where the payoff is to after thousands of years of careful strategising triumph over your enemy.

On the other side of the spectrum are execution games that test your reflexes and motor skills. These are played visually with the game continually telling the player what is going on. Here, the payoff is landing that single-frame-margin combo and watching your enemy explode into a glorious cloud of gibs. The juice that in a planning game exists in the player’s head must here be given by the game.

For realistic first-person games, juicing is difficult and labour-intensive in practice but easier in concept, as you can model the feedback off reality to align with the player’s expectations. But a side-scrolling shooter like Fish Fight is more difficult in theory. I’d doubt you have a clear picture of how stylised two-dimensional fish running and shooting each other would look in real life. For something so far detached from reality, you must work a lot in the same way as with symbol drawing: finding effects that represent their real-life counterparts without actually being them. You'll have to unhinge your expectations and think out of the box to find the feel you need.

Working with game feel

The worst part about working with game feel is that it is only ever noticed if it is bad. Good game feel is only felt, never seen. If the juice is so grandiose that the player starts thinking of it, it will wear them out and possibly even make them sick if too much stuff is moving onscreen. But if there is not enough of it, the game will feel dry and lifeless. The juice is there to constantly trigger and must therefore be just right. On that matter, juicing games is more artsy compared to, for instance, UI design. There are certain guidelines to follow, but mostly it's lots of tuning and testing. The easiest way to try the feel is simply to play the game! If even mundane actions like walking feels nice, you have really succeeded.

Juicing also regards making the world feel alive by making it respond, cause and effect, to the player's actions. Whipping up dust while running or jostling foliage when walking through it are common effects that give the impression of a breathing coherent world in which all its separate parts coexist and interact. This doesn't do anything mechanically, but is equivalent to hitting a wooden crate and it not breaking. Now you maybe even shudder a bit at the thought of how lifeless, bland and plain wrong it would feel. Well, the player too has expectations on how the world should respond. Your task is to meet and feed into those expectations on all levels, from the core greyboxed mechanics to minute tweens and particle effects.

Now, for some ways to actually squeeze some juice out of your games!

Screen Shake

Screen shake is an immensely powerful tool for giving heavy, visceral feedback that disorients the player as if their whole body was actually rumbling. When the entire scene shakes the player feels it, usually without thinking of it. Regular flatscreen games are only connected to two of the players senses, vision and hearing, and that is all you have to work with. The ears can be shaken about with some explosion noises, but to equally rustle the player’s eyes you need screen shake.

Screen shake moves the player’s viewpoint around, translationally and/or rotationally, to make it appear the world is rumbling. Adding the right amount of shake is an art; it is crucial to not overdo screen shake as it can hamper readability and even make sensitive players motion sick, but at the same time it must be significant enough to be felt. People usually have very split opinions on screen shake. Some love the punch it gives, others detest the blurry jostling. Try to take a step back and don't get too caught up in the looks, the game must still be playable.

Screen shake in practice in Fish Fight

Screen shake is a lot about feel, and as such requires a lot of dialling in. In fish fight there are three kinds of screen shake: noise (Perlin) translational, sinusoidal translational and rotational. Translational noise moves the world up- and sideways, while the rotational noise rotates the world around the screen midpoint. To that, you can also make the screen shake only in a certain axis to give it directionality. Omnidirectional shaking is the most common and can be used for pretty much everything. It fits explosions really well, but won't feel out of place for anything else either. The directional type on the other hand is more specialised and can for example be used vertically for jump impacts or horizontally for guns firing sideways. This further enhances feedback and narrows its meaning down, increasing clarity and readability.

To those types there’s three parameters: magnitude, frequency and length. Magnitude affects how far the screen moves when shaking (the amplitude of the oscillation) while frequency controls how ”many” shakes happen per second. The length decides for how long the shake will last for, and the magnitude decreases over this time to zero.

By mixing and matching different values for these parameters different effects can be made. Here are a few examples:

• Gunshot: a short omnidirectional shake with low amplitude and high frequency. This gives a small kick that doesn’t move the screen too much, just enough to confirm the firing. Fish Fight supports setting multipliers for X/Y movement, so a 1 for X and a smaller number for Y makes the player feel the direction of the action.
• Explosion: a medium-length omnidirectional shake with decent amplitude and lower frequency. This makes a kind of rumble that seriously jostles the screen. The bigger the explosive the lower the frequency!
• Jump impact: a directional sinusoidal shake makes the world bounce like a spring.

To calculate the final scene position, the current position of every active shake is added together. That value is then capped using a logarithmic function so that if many explosives go off at once, the scene does not fly off-screen. The second logarithm (log₂x) is useful for this, as it is almost linear from 0-1 and then quickly flattens.

Particles

Particles like those in games rarely occur in real life, as most of us go through our daily routine avoiding high-impact situations. But games tend to be a bit more forceful and violent, and that of course means heaps of particles! Particles are a great way to create dynamic and exciting effects that further give impact and weight to actions, but also make the world seem more alive and responsive. Some examples are sparks flying when a bullet hits a wall or dust blowing around in a storm.

In Fish Fight, macroquad-particles submodule is used to handle particles. While it might look rudimentary, it is deceptively so. With several particles, blending modes and curse pretty impressive effects can be made. The explosions in FishFight used to be entirely procedural! Now it is used for muzzle smoke, trails, bubbles and whatever other details will be added in the future.

Particle presets are stored in .json files, which can be either generated manually or using this excellent editor which provides previews and live tweaking. It might not be entirely up to date with the latest particle system format, but should get you up and running quickly.