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Alice - Dimensions and Directions

Page history last edited by Steve Sweeney 10 years, 1 month ago

The virtual world in Alice is three-dimensional (3D).  Every object in the virtual world must have its actions specified by the programmer (you).  In a way, you are the director of a movie set, where every object on the set is under your control.

 

Each object in Alice is graphically represented by a 3D Model.  Hundreds of objects are already provided with Alice, and thousands more are available online.  Thus you don't have to create them yourself (although it is possible), but you do have to understand how to use and control them.

 

Dimensions

 

Each object is defined in three dimensions:

  1. Height - the vertical distance through the object from top to bottom.
  2. Width - the horizontal distance through the object from side to side.
  3. Depth - the horizontal distance through the object from front to back.

    Each of these measurements is relative to the object itself. 

    If, for example, you have a person lying flat, their height is still the distance from their head to their feet.

     

Directions

 

Similar to the three dimensions, each object has six directions, which are also relative to the object.  They are:

  1. Up
  2. Down
  3. Right
  4. Left
  5. Forward
  6. Back

     

When an object is selected in Alice, it will be bounded by a yellow box, and three coloured lines will also be visible.  These lines indicate the directions of forward, up, and right.  For some objects, these directions are fairly obvious.  Remember, these directions are with respect to the object, or how the object would see them.  They are not from the perspective of the camera.

 

Concept:  Center

 

The center of an object is a single point, but each object is 3D. 

  • In general, the center of an object is its center of mass, or the geometric center of the object (think of the center of a cube or a sphere).
  • For objects that generally sit on the ground (e.g., people, cars, buildings), the center of the object is at the base.
  • Some objects are meant to be held or manipulated by other objects (e.g., baseball bat).  The center of these objects is at the holding point.

 

Concept:  Position

 

Every object in Alice has a center that defines its position in the world.  Even the ground has a center, which is the center of the world.  Every object's position is measured relative to the center of the world.

 

For any object (including the ground), select the object and look in the Properties panel/tab.  There will be a set of three coordiates relative to the center of the world (0,0,0).

 

Concept:  Distance

 

The distance from one object to another object is measured along a straight line between their centers.  Not all objects will have their centers on the ground, so don't assume that their distance will be along the ground either.

 

Exercises

 

The following exercises will help you practise using the concepts described above.  Remember to save each exercise in your Alice folder.  A recommended name is provided for each exercise.  Most models for each exercise are located in the default Alice gallery (called the Local Gallery).  If an object is not available, you can check the Web Gallery online, or substitute another object from the local gallery.

 

  1. Island (island.a2w)

    Create an island scene using the water world template (you could also use green grass and change the colour to blue).  Add an island and position it a bit off-center.  Add a fish to the scene (the fish may not be visible because it is behind the island or at some other blocked position).  Use the scene editor to position the fish so it looks like it is swimming in the water.

    1. Extend: animate the fish to actually swim back and forth.
    2. Extend: have the fish jump out of the water.
    3. Extend: have the fish swim around the island (advanced)

       

  2. Winter (winter.a2w)

    Add two snowmen to a snowy scene, then create a snowman stack by piling one snowman on top of the other.

    1. Extend: have the snowman on top jump in the air
    2. Extend: have the bottom snowman do a handstand while the top jumps, so they end up feet to feet
    3. Extend: jump and partially squash the snowman below; the top feet should end up on the bottom head
    4. Extend: have the snowmen switch positions

       

  3. Tea Party (teaparty.a2w)

    Alice is named after "Alice in Wonderland."  Create a scene including Alice, the White Rabbit, a dining table, three chairs, a teapot, a toaster, and a plate.

    You will need to use object methods to properly place some objects with respect to each other.  For example, to have items sit properly on the table, you might try to move them with respect to the table.

     

  4. Soldiers on Deck (soldiers.a2w)

    Add the aircraft carrier (Vehicle) and four toy soldiers (People) to a new world.  Line up the solders with a pair at each end of the deck.  Use the methods for each soldier to move the arms of each soldier to salute each other.  You can also use the scene editor to accomplish the same effect if you check the box to "affect subparts", which will allow you to manipulate parts of the soldier objects (i.e., their arms).  If you check the "affect subparts" box, remember to uncheck it when you're done!

    1. Extend:  animate the sequence so the soldiers turn to face each other and then salute

 

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