One of the great novelties that will come with SuperTuxKart Evolution is an expanded powerup set. With at least three new powerups available to players, we get greater variety within races, but also fill new niches, increasing the fun of new and experienced players alike.
Today, we are going to get a good look at the first of the new powerups: the electro-shield.
How we designed the electro-shield
The need for new powerups
The last time that SuperTuxKart saw the introduction of new powerups was in 2011 for STK 0.7.3, with the swatter and the rubber ball (that has since become the basketball).
Since then, there have been some adjustments to the behavior of some powerups and more significant changes to their distribution probabilities, but the same set of 9 powerups has been present in all versions up to the 1.x series. Some powerups are available in groups, for example it is possible to get 3 bowling balls from one gift box, but for the purpose of this discussion we are not considering it as a different powerup.
Three of the old powerups are so-called ‘global powerups’: the swapper, the parachute and the basketball. They don’t simply have an effect on the kart using them or on a nearby kart, they have an effect on all or most karts (for the swapper and the parachute) or specifically target the kart in first place (for the basketball, which can also flatten other karts on the way). As a result, they must remain fairly rare.
This leads us to a few key issues:
- Three of the remaining six powerups are attacking powerups, while only one gives a speed boost. Despite serious efforts to improve distribution for 1.0, there is only so much that can be done to limit the effect of karts in the middle of the pack slowing each other down and letting the karts in front get away.
- There is limited variety: karts in the back must get stronger powerups than those in the front, in order to give them some help in catching up. While karts in most positions can get all six normal powerups, some powerups come up much more often than others, such as bowling balls and plungers in first place or zippers and bubble gums in last place.
New powerups allow us to address both of these concerns for SuperTuxKart Evolution.
From nitro-gum to electro-shield
The electro-shield is perhaps the most important of the new powerups. Its story began in 2018 when I was considering ideas for a new powerup increasing speed.
The zipper, the existing speed-boosting powerup, gives a strong speed boost, and a triple zipper can do wonders to catch up. However, the kart also becomes much more difficult to control around corners at such speeds. For less experienced players, zippers help less to catch up than would be expected at first glance.
This observation led me to first propose the concept of a nitro-gum, combining the existing bubblegum shield with the speed and engine boosts from nitro. At the time, without the help of an artist to make something nice, it was also a way for me to make something that could easily be demonstrated and tested.
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| The nitro-gum used a blue bubblegum shield for graphics. |
But this lack of distinctive theming, as well as concerns over major gameplay changes while networking support was still being worked on, led to the concept being rejected for SuperTuxkart 1.0.
It was arguably a missed opportunity for gameplay, but it also forced us to reconsider carefully all aspects of its design and to come up with original theming.
One concept that was explored at the time but ultimately abandoned was a powerup making karts grow in size for a few seconds.
The electro-shield idea, with electric arcs surrounding the kart protectively, was later considered, but for a few years it remained dormant.
When work towards a new major version began, the idea was revived and refined.
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| An original drawing showing a crude concept of the electro-shield. The colors were used to help understand how the top-view and the side-view matched with each other. |
How it works
The electro-shield combines a speed-boosting effect with a shielding effect, and has been designed first and foremost to help less experienced players without being too strong in the hands of a good player.
The speed boost from the electro-shield is moderate but longer-lasting, making it easier to keep control of the kart.
To give some context with numbers, in SuperTuxKart Evolution nitro gives a speed boost of around 20% to the base max speed, a zipper gives up to 48% (over 60% in 1.5), while the electro-shield boost is only around 12%. On the other hand, the effect duration of 8 seconds significantly exceeds that of a zipper or of a typical nitro burst.
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| A visual comparison of the speed curves from using a zipper, an electro-shield and a big nitro can, without other sources of speed increase or decrease. |
The speed boost is supplemented by a significant boost to kart acceleration. If no mistake is made, this matters little, but if the kart hits a wall, goes off-road, etc., the better acceleration saves significant time. This is a crucial part of its design to make it more forgiving for newer players.
The shielding effect also makes the powerup more forgiving. It is not a full immunity: after protecting from a threat, the shield is disrupted and dissipates, also ending the speed boost. This is a design choice, keeping a measure of skill in play: there is still an incentive for the player with the electro-shield to avoid danger, and for other players to try and attack.
Nonetheless, even without full immunity, avoiding the time loss from an explosion, a banana, or various other threats, still serves the powerup’s general purpose: helping players in bad positions to catch up.
Note that, unlike the bubblegum shield, the electro-shield doesn’t protect when driving on gums. The acceleration boost, however, helps to recover quicker.
To top it off, the electro-shield offers a 35% reduction to off-road penalties. In a few places this can allow players to gain a bit of time with an off-road shortcut, but it is mainly intended to reduce how much time is lost by newbies accidentally driving off the road.
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| Although the electro-shield gives less speed than nitro on normal roads, here in this off-road section it’s faster, as can be seen on the speedometers. |
The electro-shield is distributed to karts in the back half of the race to give them a chance to come back. This also helps making the change in available powerups with kart position more tangible.
The electro-shield’s visual design
The electro-shield also brings a new level of attention to visual detail for a SuperTuxKart powerup.
Initial concepts with electrical arcs surrounding the kart were devised, but for what we envisioned, a simple mesh as used by existing attachments, such as the swatter, was insufficient.
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| An early version using only a basic mesh. |
SuperTuxKart already had the concept of library nodes, a collection of related elements attached to a common parent, allowing them to move together, and to be made visible or hidden together, but they were deeply tied to tracks. Animated textures also assumed they would be used by a track.
Allowing the use of library nodes as kart attachments entailed significant code changes, and it was a challenge to make all the small details work properly.
As a result of this work, any existing library object can be made attachable if so desired. Attachable library nodes are loaded once, and copies are then made on demand when a kart needs it.
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| The parrot on Suzanne's kart is an attached library object. |
The final version of the electro-shield takes full advantage of these capabilities, with a combination of several elements working together:
- Electric arcs surrounding the kart, using animated textures to move continuously,
- Metal coils floating around the kart anchoring the electric arcs,
- A small blueish light that shines on the kart and its immediate surroundings,
- Small electrical sparks,
- Occasional random electric arcs moving away from the shield itself.
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Like the bubblegum shield, the electro-shield scales to adapt to the size of the kart it is protecting. Uniquely, height-scaling is separate from its length- and width-scaling, to better accommodate karts that are relatively tall for their length and width.
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| The electro-shield's shape adapts to the kart. |
There are still some details we want to improve for the main release of SuperTuxKart Evolution, such as bespoke animations when the electro-shield is activated or disabled, a new icon, as well as custom sound effects.
Some other tiny visual details, such as the metal coils sometimes visibly going through obstacles, would be nice to address but are a lesser priority with our limited manpower. Although we prioritize quality over strict deadlines, we also want to make SuperTuxKart Evolution available to players as soon as we can, and therefore have to consider where our efforts will produce the greatest benefits.
Conclusion
With the electro-shield as an additional tool for players in the back to recover, SuperTuxKart Evolution makes races more dynamic.
It is a fine balancing act between making the game more approachable to new players, who often enjoy getting strong bonuses, and satisfying experienced players who want driving skills to play an important role.
Although the optimal point is subjective, a lot of care has been taken to significantly improve the enjoyment of all kinds of players.
In future blog posts, we will also take a look at the nitro-hack and the mini-wish, two other new Evolution powerups that further add variety and strategic choice to the mix.
SuperTuxKart now also has a Patreon where everyone can get access for free to small news about the development of STK Evolution, so check it out!
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