andy%reyes%(desma157b)% analysis of game object display...

Andy Reyes (DESMA 157B) March 1, 2010

Analysis of Game Object Display and Collision Behavior in Top-Down Adventure Games


Pokémon: Red and Blue Versions Gameboy (1996) Genre and Gameplay: Third-person top-down RPG adventure game focusing on exploration, item collecting, and turn-based Pokémon battles. Plot: You and your hometown rival have just become new Pokémon trainers and are sent off to capture and train Pokémon, complete your in-game Pokémon encyclopedia known as the Pokédex, battle and defeat all of the Pokémon Gym Leaders, and try your hand at defeating the Elite Four and the Pokémon Champion. The overall player motivation in this game is to become a Pokémon Master by collecting all 151 species of Pokémon and leveling up your team to become undefeatable. Art and Graphics: Pokémon Red and Blue for the Gameboy features 8-bit grayscale graphics. Although many NPCs and trainers look nearly identical, the

game boasts 151 unique Pokémon designs, each with a unique sound and Pokédex description. Each Pokémon is iconic and memorable to the point where most players know each of them by heart, along with their evolution cycles and even signature moves. The graphics for each monster’s attack is not very flashy and mostly involve

moving the sprites in different ways and changing color schemes. This can be seen as a regrettable hardware limitation, or as a way for players to use their imaginations as how each attack would look in real life. Controls: 4-way directional pad for movement, plus A and B buttons for navigating menus and interacting with NPCs, and also Start and Select buttons for Save menus. Collision Commentary: The top-down camera angle of the game encourages exploration of the various towns and field areas where Pokémon lay hidden. However, the game has rudimentary wall and scenery collision behavior, but only because there is not much the player can interact with in the overworld. For example, the main character, nor any NCPs can walk behind bookcases.


The Legend of Zelda: A Link to the Past SNES (1991) Genre and Gameplay: Third-person top-down action-adventure game focusing on exploration, item collecting, dungeon crawling, and puzzle solving. Plot: After hearing a strange voice call out to him in a dream, a young boy named Link wakes up to find his uncle heading out in a rainstorm to rescue Princess Zelda from a takeover of her Castle. He tells Link to stay put, but not long after he leaves, Link decides to help him in any way you can and follows him. When you find Link’s uncle again, his dying words reveal Link must save the land of Hyrule at any cost. After Zelda gets kidnapped by the evil Wizard Aghanim, Link must travel between the Light and Dark Worlds to free the descendents of the Seven Sages to save Zelda and restore Hyrule to its former glory. Art and Graphics: The Legend of Zelda: A Link to the Past for the Super Nintendo Entertainment System features 16-bit sprite graphics. The sheer size and scope of the game’s world can be attributed to Nintendo EAD using cartridges with 8-megabits of memory as opposed to the 4-megabit cartridges of the time. To save memory, they compressed the game’s graphics tiles to have only 8 colors instead of the usual 16 the SNES provides. Luckily, the overworld, dungeons, items, baddies, and NPCs are all varied enough so that the player does not notice the lack of color variety. Controls: 8-way navigation on a 4-way directional pad, A button for context-sensitive interactions, B button for swinging Link’s sword, X button to bring up the map, and the Y button to use an assigned item. L and R are used to toggle a close-up map and a full-world map, and Start and Select both pause the game, but Start brings up the save game menu screen while Select brings up the in-game menu screen. Collision Commentary: As with Pokémon, the top-down view allowed the player to get a sense of the overall world. Bad guys, plants, stones, trees, and tombstones are only a fraction of the things Link can interact with. This near-constant interaction prompted Nintendo to add an extra sense of depth using an interesting collision trick, which allowed Link to appear to be behind certain objects, even though that is never really the case.


Banjo-Kazooie: Grunty’s Revenge Gameboy Advance (2003) Genre and Gameplay: Third-person top-down adventure platformer focusing mainly on item collecting and fighting monsters. Plot: Two months after the events in the prequel Banjo-Kazooie have transpired, the evil witch Gruntilda, who was trapped under a boulder in the first game, is back in a mechanical body possessing her soul. Wanting revenge on Banjo and Kazooie for foiling her plot, she sends Kazooie back in time to prevent Banjo and Kazooie from meeting each other. With the help of the local shaman Mumbo Jumbo, Banjo is able to travel back in time as well to rescue Kazooie and defeat the witch again. Art and Graphics: Banjo-Kazooie on the Gameboy Advance features 16-bit sprite graphics. The game is top-down and uses some 3D modeling in order to accurately and truthfully represent Spiral Mountain and other locations in the

Nintendo 64 game using the Gameboy Advance. They pulled it off quite nicely as all of the locations shared in common between the two games are recognizable. Because of the compression and color schemes used in certain levels, it is sometimes extremely difficult to tell the differences between walls, floors, and bad guys. This leaves the player extremely disoriented.

Controls: 8-way navigation on a 4-way directional pad, A, B, L, and R buttons are used in combination to perform actions such as jumping, flapping, shooting eggs, and using items such as springs and drills. There are an impressive variety of actions Banjo and Kazooie can perform together. Collision Commentary: This game is different from the other two in that objects are made to seem as 3-dimensional as possible. Therefore, Banjo-Kazooie uses a different style of collision detection when it comes to scenery and objects in the overworld. In this game, you can go directly behind objects, obstructing the camera’s view of the player. This may be because the levels and objects are created in 3D to begin with. This style of collision detection is somewhat annoying since the player will sometimes lose the character behind giant cliffs.


Game Comparison There are many ways to implement wall and object behaviors in games. What is most important is objects that are in front of other objects are displayed “on top”, while the object being stood in front of is “on the bottom” relative to the top-down view of the screen. This creates the illusion that an object is in front of something else in a 2D top-down game, when really they are simply being displayed one on top of the other. For the most part, objects will remain in their top-down location to preserve the quality of what other objects are allowed to go “on top” and “below” them. All of these games mentioned vary in the way they decide to display objects in the physical world and how they interact with player and non-player characters. On the one hand, we have Pokémon, which refuses to let the player move behind any object (with the exception of NCPs and tall grass). This means that for the most part, “topness” priority is given to the player and NPCs. Since the player can walk in front of buildings and objects, they must be displayed on top. However, if one were to try to approach a building from behind, the player would not disappear behind the building, they would really appear to be on top of the building at all times. What prevents this from happening is proper collision detection that does not allow the player to occupy the same space as the top of the building. As for Zelda, they employ an interesting alternative to the restricting rules that Pokémon adheres to. Instead of each game object really being just one sprite with only one “topness” level, most of them are made up of multiple sprite images overlayed on top of each other, and each of them have their own “topness” value. A great example of this is trees. In Pokémon, you can only walk in front of trees and bushes, but never behind them. In Zelda, trees consist of the trunk and the top part of the tree I will call the “leaves.” Link interacts with the trunk normally, where he can walk in front of, but not behind the trunk. But the leaves of the tree will always be “on top of” Link. No matter where he stands in the game, he will never be in front of the leaves of the tree. This gives


the illusion of Link being able to go behind trees and obscuring himself from view. This adds what seems to be depth to the the game’s top-down perspective.

Zelda also employs a few other tricks to give an illusion of depth. When rescuing Zelda in the first few minutes of gameplay, there is a cage which you appear to be able to stand in front of and behind. When standing behind the iron bars, you see Link through them as you would expect. But how could Link stand in front of and behind the bars if each object only has one “topness” level. Either the bars are always behind Link or the bars are in front of him. It cannot be both! Well, if you look closely at the image above, you will see that Link is actually not standing in front of the bars. He is blocked off by an extra object on the ground that is colliding with him before his sprite and the bars’ sprite occupy the same space. Because they do not occupy the same space, it is not revealed that the bars are actually always on top of Link, but once you gain access inside the cell, the bars will display on top of Link as expected for this top-down perspective.


Banjo-Kazooie is different from the previous two games in that it actually uses 3D modeling to create certain objects. Since 3D objects truly do have a “behind” and “in front,” not very many tricks are necessary to create the illusion of 3D. This is an excellent design point on their part since they are bringing a 3D world from the Nintendo 64 and transforming

it into a quasi-2D world on the Gameboy Advance. Having the same freedoms as a true 3D game in a 2D game is liberating and makes the game feel bigger than it actually is. Instead of restricting where the player can and cannot go by arbitrary boundaries, the objects themselves create those boundaries as they would in real life.

When Banjo walks behind statues, he is actually behind the statue. A downside to this is confusion for the player when standing behind ledges and tall areas. In the image to the left, Banjo can easily walk behind the ledges seen in the foreground. This would give opportunities for the developers to

provide secret items and powerups to help the player if the player decides to explore what they cannot see. For each of these games, the developers had to decide how they would present the world to the player and how objects would behave in physical space. It is these seemingly insignificant implementation differences that set the boundaries for a game and its characters. In each of these games, the developers made very wise decisions. But a single mistake in this area can make a great game into an incredible flop.

andy%reyes%(desma157b)% analysis of game object display...

Documents