SPRITES

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SPRITES

• By Jaime Gamarra
• CS 536

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Motivation

• I stumbled upon the sprite concept while looking
  on how to create a HUD (Heads-up-display) for my
  current game project.
• A HUD is one way to transmit game, character or
  miscellaneous information on the screen to the
  player.
• Possible information to display on a HUD
  players score, health, lives left, etc

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HUD Sprite Relationship

• HUDs are frequently rendered with a 2D look,
  often using sprites.
• OK, so what are sprites??
• Sprite Two dimensional image or animation that
  is integrated into a larger scene.
• Sprites originated in 2D games, they can be both
  hardware or software generated.

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Sprites on 3D games

• Here is an example of sprite usage on a 3D game,
  notice the cloud and the three plants in this
  scene are actually textured flat planes.

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Sprites and 3D

• Sprites used on modern 3D games are animations in
  the form of textured planes, these planes are
  always facing the camera.
• Additionally, they can be scaled, occluded and
  moved two dimensionally.
• This approach is also known as billboarding (As
  seen in class notes).

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When to use sprites

• Because of its two-dimensional nature, sprites
  are better used when appearing for short periods
  of time in a game (If used to simulate a 3D
  effect).
• Camera rotation can easily give away the fact
  that a sprite is not three dimensional.
• Effectively used when applied to mimic an
  spherical-like object or an object whose
  appearance is constant regardless of view.

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Another Sprite Example

• Sprite usage featured on the game Viewtiful Joe
  for gamecube. The sprite used depicts a hit with
  a number value.

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More On Sprites

• Sprites can be created from pre-rendered CGI, 3D
  graphics, vector art and text (Mostly as
  backgrounds that are rendered in the production
  stage as opposed to while real game-play takes
  place). It is done mainly to improve performance.
• Performance boost Most 3D engines can process
  sprites much faster than 3D objects.

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Animated Sprites

• I found a project that used animated sprites
  (www.codesampler.com). It can be taken as a good
  reference point for those of you thinking on
  using a HUD as an advanced feature for your game.
• It can also be seen as a method to apply a
  good-looking effect at a relatively low
  performance cost.

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Background Information Rendering Sprites

• Set 3D projection and draw 3D objects first (Do
  this on one projection matrix).
• Have a second projection matrix to render the
  sprites.
• In this site and this discussion post, the
  rendering of a HUD is done using glOrtho()
• http//osdl.sourceforge.net/OSDL/OSDL-0.3/src/doc/
  web/main/documentation/rendering/SDL-openGL.html
• http//www.gamedev.net/community/forums/topic.asp?
  topic_id388298

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Sprites data structure

• Sprites, like 3D models, have to posses some kind
  of data structure that will hold all pertinent
  information on the sprite, examples of sprites
  classes or structures can be easily found on the
  web.
• Such structure generally contains coordinates,
  width, height, number of frames, texture info and
  any other data that may be application-specific.

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Now on to a demo

• Definitions and sources taken from
  http//en.wikipedia.org/wiki/Sprite_28computer_gr
  aphics29