Creating the gravity-changing gameplay in Flip's Twisted World
The idea for Flip's main mechanic – the ability to twist the world, turning gravity on end – came to me from the works of M. C. Escher. Escher was a Dutch artist famous for his mind-bending optical illusions. One of his most famous works is a lithograph titled Relativity, which shows a mixed-up room with stairways, doors, and windows at all sides and all angles, complete with figures happily walking up the "walls" as they go about their daily activities.
Escher's RelativityI'd long been intrigued by this piece of art (okay, I confess, I fell in love with it ever since the movie Labyrinth, starring Davie Bowie), and wanted to find a way to experience a twisted-up world like that, in a game. What if you could change your gravity at will, walking up walls and ceilings to reach your goal?
So I came up with a set of game mechanics:
• You can twist the world in 90 degree increments. So a wall becomes a flat floor for you to fall onto, not a ramp to slide off of. Also, you can't go straight from floor-to-ceiling, a limit we exploit in our puzzles.
• You can only twist in the cardinal directions. Again so you land flat on a wall, not wedged in a corner. This means you can look for twisting opportunities by keeping an eye on what is directly north, east, south, and west.
• If you fall too far, you're set back. Otherwise players could just drop themselves straight to the goal. We keep the penalty light, though, so nobody is punished for exploring and trying new ideas.
• Some nearby objects will twist with you. This lets you use your control over gravity to move things you can't reach, bringing a whole new set of challenges and techniques into play.
It's amazing what you can do with just those four rules. With one twist, walls become floors, pits become paths, and obstacles become opportunities. It completely changes the way players move around 3D worlds.
Even so, my first attempt at a game with these mechanics was... clunky. I was working alone in Flash, and even simple levels got hard to see and move around. The number of different ways to twist a cube-shaped room meant a lot of confusing buttons around the screen, and the visuals and character design were rather lacking too.
The original Flash demo.How You've Turned my World...
When I joined up with Frozen North Productions and developing on the Wii became a possibility, we all saw a natural fit. With the Wii Remote's gesture recognition we could literally put the world in the palm of players' hands, letting them twist the world in true 3D with a flick of the wrist. Taking advantage of the Wii's graphical power, combined with Frozen North's incredible art team, we would be able to create rich, vibrant 3D worlds, solving the visual issues in my early, low-tech prototypes.
The next challenge was figuring out how to use the Wii to capture the gestures we needed. Unfortunately, it's not as easy as waiting for the remote to tell the game "I've been twisted left!" The Wii Remote doesn't know what "left" is (or "twisting" for that matter, though the new Wii MotionPlus helps there). All the Wii Remote can tell us is acceleration. Inside there are three accelerometers that tell you how much the remote is accelerating in the x, y, and z dimensions.Not all acceleration is movement, though. The Earth's gravity shows up as acceleration even when the Wii Remote is still, and moving it a constant speed doesn't show up as acceleration at all.
Have trouble visualizing it? I was too, so I had to build some tools to help see what different kinds of twists and turns "look" like visually, in terms of acceleration.
The Wii Remote Acceleration ChartThe answer is: they don't look like very much at all. The trouble we discovered is that everyone holds the Wii Remote a little differently. While I hold it tilted a little to the right, one of our programmers holds it pointed almost straight up. The acceleration pattern I get when I turn left looks like what he gets if he goes right.
Getting to Know You
Our trick to solve this was to have the game learn how the player likes to hold the Wii Remote. Whenever the Wii Remote isn't moving much, we use the acceleration from the Earth's gravity to make a guess at how the player is holding it. Bit by bit, that guess gets better over time. Then, using a handy math trick, we subtract that "rest" position from the acceleration while the player is twisting, giving us a standard-looking acceleration pattern, no matter how the player was holding the Wii Remote at the start.
It's not perfect. If you normally hold the Wii Remote upside-down when you play (ouch), you might find twisting the world acts a bit weird. Changing your pose right before you twist can cause problems too, because the game hasn't had enough time to learn your new "rest" pose. When in doubt, give it a second and try again – we're pretty happy with how quickly it corrects itself.
Look Before You Twist
The final step in getting the twisting feeling just right was to make sure the player can see which way the world is about to turn before it does. This is done with a pair of glowing arrows that orbit the character Flip whenever the player is holding the B button, about to twist the world. The direction the arrows spin shows which way Flip will fall once the gravity changes, and their colour shows whether or not it's a good idea. When they're blue, Flip is on track to land safely. When the arrows turn orange, it means twisting that way could leave Flip falling into the sky. If players decides not to twist after all, they can turn the Wii Remote back to their rest position and the arrows will disappear, showing that it's safe to release the B button without gravity changing.
The choice of orange and blue, incidentally, rather than red and green, is to make sure the game is fun for colour-blind players. The most common form of colour-blindness makes it difficult to tell the difference between red and green, but most colour-blind people can distinguish blue and orange pretty reliably. Thinking hard about details like these keeps the game fair and fun for everyone.
On that note, you may be feeling angry if you're a gamer who doesn't like using gesture controls at all. Not to worry: if you don't like using gestures, you can use the analog stick instead. We were thinking of you too!
Let's Do the Twist
You'll get a chance to try it yourself September 21, when Flip's Twisted World hits store shelves. On behalf of the whole team here at Frozen North Productions, I hope you have a great time putting the world in the palm of your hand, and seeing where a little twist can take you!
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Douglas Gregory is Frozen North Productions' Lead Designer. Doug has a passion for math and art and all the places they intersect, and is the brain behind the core game mechanics and visual material effects in Flip's Twisted World.
