Flesh out protocol description
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Sam Caldwell
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Layers:
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- External Events
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* key press/release
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key press/release (interrupts from the outside world)
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- Ground
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corresponds to computer itself - device drivers and applications
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corresponds to computer itself
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device drivers
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applications
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- Game
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running application
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per-game state, such as score and count-of-deaths
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process which spawns levels
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running application
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per-game state, such as score and count-of-deaths
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process which spawns levels
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regular frame ticker
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- Level
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model of the game world
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actors represent entities in the world, mostly
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misc actors do physicsish things
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model of the game world
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actors represent entities in the world, mostly
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misc actors do physicsish things
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## Common Data Definitions
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A Vec is a (vec Number Number)
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A Point is a (point Number Number)
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## Ground Layer Protocols
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- Rendering
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- assertion: Sprite
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- assertion: ScrollOffset
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- assertion: ScreenSize
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- role: Renderer
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Responds to FrameDescription by drawing the current set of Sprites,
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adjusted via the current ScrollOffset, in a window sized by ScreenSize.
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- Keyboard State
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- message: KeyStateChangeEvent (external event)
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- assertion: KeyDown
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- role: KeyboardIntegrator
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Receives KeyStateChangeEvent from outer space, summing them to
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maintain collections of KeyDown assertions.
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- Timer
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(standard system driver & protocol)
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- Frame Counting
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- message: FrameDescription
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- role: FrameCounter
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Arranges for, and responds to, system timer events, issuing
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FrameDescriptions at regular intervals (a constant compiled-in
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frames-per-second value).
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A Sprite is a (sprite (Nat -> Pict) Number Number Nat)
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where sprite-renderer produces a pict, given a frame number
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sprite-x is the X coordinate in world coordinates for sprite's top-left
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sprite-y is the Y coordinate in world coordinates for sprite's top-left
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sprite-layer is the layer number for the sprite, more negative for closer
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to the camera.
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A ScrollOffset is a (scroll-offset Vec), indicating the vector to *subtract*
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from world coordinates to get device coordinates.
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A ScreenSize is a (screen-size Vec), indicating the size of the device.
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The coordinate systems:
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World coordinates = the large virtual canvas, origin at top-left,
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x increases right and y increases down
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Device coordinates = the window's coordinates, mapped to world coords
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via scroll offset & clipping
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In both, layer numbers are more positive further away from the camera.
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A KeyStateChangeEvent is either
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- (key-press KeyEvent) ;; from 2htdp
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- (key-release KeyEvent)
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signalling a key state change.
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A KeyDown is a (key-down KeyEvent), an assertion indicating that the
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named key is currently being held down.
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A FrameDescription is a (frame Nat), a message (!)
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indicating a boundary between frames; that is, that frame number frame-number
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is just about to begin.
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## Game Layer Protocols
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- Scoring
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- message: AddToScore
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- assertion: CurrentScore
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- role: ScoreKeeper
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Maintains the score as private state.
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Publishes the score using a CurrentScore.
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Responds to AddToScore by updating the score.
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- Level Spawning
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- assertion: LevelRunning
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- message: LevelCompleted
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- role: LevelSpawner
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Maintains the current level number as private state.
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Spawns a new Level when required.
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Monitors LevelRunning - when it drops, the level is over.
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Receives LevelCompleted messages. If LevelRunning drops without
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a LevelCompleted having arrived, the level ended in failure and
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should be restarted. If LevelComplete arrived before LevelRunning
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dropped, the level was completed successfully, and the next level
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should be presented.
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- role: Level
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Running level instance. Maintains LevelRunning while it's still
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going. Sends LevelCompleted if the player successfully completed
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the level.
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An AddToScore is an (add-to-score Number), a message
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which signals a need to add the given number to the player's
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current score.
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A CurrentScore is a (current-score Number), an assertion
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indicating the player's current score.
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A LevelRunning is a (level-running), an assertion indicating that the
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current level is still in progress.
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A LevelCompleted is a (level-completed), a message indicating that
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the current level was *successfully* completed before it terminated.
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## Level Layer Protocols
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- Movement and Physics
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- message: JumpRequest
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- assertion: Impulse
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- assertion: Velocity
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- assertion: Position
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- assertion: Massive
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- assertion: Attribute
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- assertion: InitialPosition
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- role: PhysicsEngine
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Maintains positions, velocities and accelerations of all GamePieces.
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Uses InitialPosition to place a piece at its creation.
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Publishes Velocity and Position to match.
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Listens to FrameDescription, using it to advance the simulation.
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Takes Impulses as the baseline for moving GamePieces around.
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For Massive GamePieces, applies gravitational acceleration.
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Computes collisions between GamePieces.
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Uses Attributed Aspects of GamePieces to decide what to do in response.
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Sometimes, this involves sending Damage.
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Responds to JumpRequest by checking whether the named piece is in a
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jumpable location, and sets its upward velocity negative if so.
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Consumer of LevelSize to figure out regions where, if a GamePiece
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crosses into them, Damage should be dealt to the piece.
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When the player touches a goal, sends LevelCompleted one layer out and
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then kills the world. When the player vanishes from the board, kills
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the world.
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- role: GamePiece
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Maintains private state. Asserts Impulse to move around, asserts Massive
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and Attribute as required, asserts InitialPosition to get things
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started. May issue JumpRequests at any time. Represents both the player,
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enemies, the goal(s), and platforms and blocks in the environment.
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Asserts a Sprite two layers out to render itself.
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- Player State
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- message: Damage
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- assertion: Health
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- role: Player
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Maintains hitpoints, which it reflects using Health.
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Responds to Damage.
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When hitpoints drop low enough, removes the player from the board.
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- World State
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- assertion: LevelSize
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- role: DisplayControl
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Maintains a LevelSize assertion.
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Observes the Position of the player, and computes and maintains a
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ScrollOffset two layers out, to match.
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An ID is a Symbol; the special symbol 'player indicates the player's avatar.
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Gensyms from (gensym 'enemy) name enemies, etc.
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A JumpRequest is a (jump-request ID), a message indicating a *request* to jump,
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not necessarily honoured by the physics engine.
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An Impulse is an (impulse ID Vec), an assertion indicating a contribution to
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the net *requested* velocity of the given gamepiece.
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A Velocity is a (velocity ID Vec), an assertion describing the net *actual*
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velocity of the named gamepiece.
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A Position is a (position ID Point), an assertion describing the current actual
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position of the named gamepiece.
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A Massive is a (massive ID), an assertion noting that the named gamepiece
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should be subject to the effects of gravity.
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An Attribute is an (attribute ID Aspect), an assertion describing some aspect of
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the named gamepiece
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An Aspect is either
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- 'player -- the named piece is a player avatar
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- 'enemy - the named piece is an enemy
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- 'solid - the named piece can be stood on / jumped from
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- 'goal - the named piece, if touched, causes the level to
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End The Game In Victory
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An InitialPosition is an (initial-position ID Point), an assertion specifying
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not only the *existence* but also the initial position (in World coordinates)
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of the named gamepiece.
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A Damage is a (damage ID Number), a message indicating an event that should
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consume the given number of health points of the named gamepiece.
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A Health is a (health ID Number), an assertion describing the current hitpoints
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of the named gamepiece.
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A LevelSize is a (level-size Vec), an assertion describing the right-hand and
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bottom edges of the level canvas (in World coordinates).
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-----------
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Interaction Diagrams (to be refactored into the description later)
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================================================================================
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title Jump Sequence
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@ -38,7 +239,7 @@ Physics -> Subscribers: (vel 'player ...)
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Physics -> Subscribers: (pos 'player ...)
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================================================================================
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title Display Control Updates
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@ -46,11 +247,38 @@ Physics -> DisplayCtl: (pos 'player ...)
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note right of DisplayCtl: Compares player pos to level size
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DisplayCtl -> Subscribers: (at-meta (at-meta (scroll-offset ...)))
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================================================================================
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title Movement Sequence
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Moveable -> Physics: (massive ID)
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Moveable -> Physics: (attr ID ...)
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Moveable -> Physics: (impulse ID vec)
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note right of Physics: Processes simulation normally
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Physics -> Subscribers: (pos ID ...)
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Physics -> Subscribers: (vel ID ...)
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================================================================================
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title Keyboard Interpretation
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Keyboard -> Player: (press right-arrow)
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Player -->> Physics: assert (impulse ID (vec DX 0))
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note right of Physics: Processes simulation normally
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Keyboard -> Player: (press left-arrow)
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Player -->> Physics: assert (impulse ID (vec 0 0))
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Keyboard -> Player: (release right-arrow)
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Player -->> Physics: assert (impulse ID (vec -DX 0))
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Keyboard -> Player: (press space)
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Player -> Physics: (jump)
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|#
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|#
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(struct velocity (id vect) #:prefab)
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(struct damage (id pts) #:prefab)
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(struct attr (id
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