Pueblo developer examples

This document contains explanations of several example Pueblo servers, including source code, etc.

Spinning Monolith

These examples all use the URL:

    http://www.chaco.com/pueblo/vrml/demo/monolith/monolith.wrl

When the user contacts the server (attaches to a port, enters a room in a mud, etc), she receives this line of IHTML:

    <img xch_graph=load
         href="http://www.chaco.com/pueblo/vrml/demo/monolith/monolith.wrl">

The VRML file contains this node (among others):

    DEF Monolith_rotation Transform { rotation 0 1 0 0 }

This node is replaced periodically by the Pueblo server with a new version of this node in which the rotation angle is replaced with a new value (which is incremented in the Pueblo server before each replacement is sent). For example:

    <img xch_graph_node="DEF Monolith_rotation Transform { rotation 0 1 0 1.3 }">
    <img xch_graph_node="DEF Monolith_rotation Transform { rotation 0 1 0 1.4 }">
    <img xch_graph_node="DEF Monolith_rotation Transform { rotation 0 1 0 1.5 }">

The server may also output a "synchronous draw" command to the Pueblo client, to be sure the monolith animation is drawn. This is optional, and for the monolith example, you probably don't want this synchronous behavior (so the monolith might skip a "frame" of the "animation" if it's busy doing something else during a frame). For situations where each frame of an animation must be displayed, this is how to accomplish it:

    <img xch_graph=draw>

Spinning Monolith in Perl

This example works as a standalone server which listens on a port (4545 by default), accepts connections from multiple users, and displays a shared view of the monolith, spinning away. This is like a persistent CGI script waiting on a port instead of being run by an HTTP server.

Here's the source.

This server is running on zuni.chaco.com, port 4545. Just point a Pueblo client at it to see what happens.

Spinning Monolith in TinyMUSH

This object handles the rotation generation, and assumes that when you walked into the room, you loaded the appropriate URL for the monolith.

(In TinyMUSH, the command '&attrname objname=value' sets the 'attrname' attribute of the object 'objname' to 'value'.)

    @@  Create the object
    @create Rotation
    @@  Lock it so only you can pick it up
    @lock Rotation==me
    @@  When the MUSH starts up, trigger
    @@  the rotation timer.
    @Startup Rotation=@trig me/rotate_timer
    @@  The 'ROTATE' attribute does several
    @@  commands when it's '@trig'ed:
    @@    1.  Increment the Rotation object's own
    @@        "angle_val" attribute by 0.2
    @@    2.  Emit the node replacement to
    @@        everyone in the room.
    &ROTATE Rotation=&angle_val me=[add(v(angle_val),.2)];@emit/noreturn <img xch_graph_node="DEF Monolith_rotation Transform \{ rotation 0 1 0 [v(angle_val)]\}">
    @@  The 'ROTATE_TIMER' attribute is triggered when
    @@  the MUSH starts up, and triggers the 'ROTATE'
    @@  attribute, then waits 1 second and triggers
    @@  itself.
    &ROTATE_TIMER Rotation=@trig me/rotate;@wait 1=@trig me/rotate_timer

8-Queens Puzzle (in TinyMush)

The 8-Queens puzzle is a "standard" computer science puzzle-game in which a player is asked to place 8 chess "queens" onto an 8x8 chess board such that no queen can "kill" any other. It's also a reasonably simple Pueblo game to implement, even for multiple users.

This implementation of 8-Queens is in TinyMUSH, which is a fairly grotesque language, but is okay for rapid-prototyping things like this.

The VRML file used is at this URL:

    http://www.chaco.com/pueblo/vrml/pueblo/queens/board.wrl

The board

Each of the squares on the board is an anchor like this one:

    WWWAnchor {
        DEF xch_cmd Info { string "place 0 0" }
        IndexedFaceSet { coordIndex [ 0, 1, 10, 9, -1, ] }
    }

The Info node named xch_cmd contains a "command" which is sent to the Pueblo server when the user clicks on the anchor. In the 8-queens puzzle, each board location has a command of the form "place <x-coord> <y-coord>". When the chess server receives this command, it extracts the x and y coordinates of the board position, and places a queen at that location.

The queens

Each queen in the scene consists of a construct like this:

    Separator {
        DEF Q0_transform Transform { translation 0 0 0 scaleFactor 0 0 0 }
        DEF Queen WWWInline { name "queenbig.wrl" }
    }

(the other queens all USE Queen instead of DEF'ing Queen.)

The Transform node named "Q0_transform" (or, more generally, "Q<queen-number>_transform") is used to scale and place the queen. Since the current version of Pueblo only supports replacement of transformation nodes (Transform, Rotation, etc.), we cannot just "add" a queen to the scene and "delete" a queen from the scene at will. To get around this, we set the scaleFactor of queens we want to be invisible to '0 0 0', changing the scaleFactor to '1 1 1' when we want them to appear.

So, to place Queen number 3 at location (2, 5), the 8-queens Pueblo server would output this:

    <img xch_graph_node="DEF Q3_transform { translation 2 0 5 scaleFactor 1 1 1 }">

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