Analysis of Game Object Display and Collision

Andy Reyes (DESMA 157B) March 1, 2010 Analysis of Game
Object Display and
Collision Behavior in
Top-Down Adventure
Games
Andy Reyes (DESMA 157B) March 1, 2010 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.
Andy Reyes (DESMA 157B) March 1, 2010 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 contextsensitive 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 ingame 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 nearconstant 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.
Andy Reyes (DESMA 157B) March 1, 2010 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.
Andy Reyes (DESMA 157B) March 1, 2010 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
Andy Reyes (DESMA 157B) March 1, 2010 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 topdown 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.
Andy Reyes (DESMA 157B) March 1, 2010 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.