XNACS1Lib:
Tutorial 3: Working With PrimitiveSet

Reference: This is the third tutorial on how to work with the XNACS1Lib library. It is assumed you have read and understand the previous two tutorials:

• First Tutorial : XNACS1Lib application structure; and
• Second Tutorial: Working with primitives

Goals : This tutorial concentrates on illustrating working with PrimitiveSet for controlling the visibility (membership with AutoDrawSet) of any related set of primitives, and on the Random number utilities:

• PrimitiveSet:  Logical entity for grouping related Primitive for the purpose of showing/hiding these Primitives. As a programmer you are responsible for ensuring each Primitive belongs to at most one PrimitiveSet.
• Random number utilities: randomness is a convenient tool for many interactive graphical applications. XNACS1Lib supports random number generation.

1. Obtain the example code

• Here is the zip file to the source files and compiled executable of this example.
• Here is the keyboard mapping for the XBOX 360 controller.  
• Here is the main tutorial page for working with XNACS1Lib, and here is the complete documentation of the library: html-page or compiled html help file.

1. Button-X: hides/un-hides the ladder and the pink-ish circle.
2. Random speed of the soccer ball after each collision with the ladder.

2. The Source Code Files/Structure

Take a look at the ExampleProgram folder that you have unzipped and you will see a structure identical to that of previous tutorials. Once again, you can double click on the *.sln file to launch the IDE, we will concentrate on the Game1.cs file where all the relevant source code are located.

3. Examine Game1.cs Structure:

When you open the Game1.cs file in the IDE, you will see source code structure that is very similar to that of the second tutorial:

? Reference to libraries ? namespace XNACS1Lib_PrimitiveSet {     public class Game1 : XNACS1Base {         #region Instance Variables         #endregion         protected override void   InitializeWorld()         protected override void UpdateWorld()     } }

Once again, we will examine each of : Instance Variables , InitializeWorld() , and UpdateWorld() in details and understand how to implement the behaviors we have observed.

4. Examine Instance Variables of Game1.cs

When you expand the Instance Variable region, you will observe:

#region Instance Variables    ... SPEED ... and A B C D that are identical to previous tutorial ...    XNACS1PrimitiveSet m_VisibleSet;    // E. Button-X click makes this set invisible    bool m_SetIsVisible;                 //    Records if the set is currently visible #endregion

The five sets of instance variables: A to E where variable sets A to D are identical to previous tutorial. E: ( m_VisibleSet ) is a logical set that lets us insert related Primitives and control the visibility of the Primitives as a set.

5. Examine InitializeWorld() function of Game1.cs

The InitializeWorld() function is once again very similar to previous tutorial:

protected override void   InitializeWorld() {     SetWorldCoordinate( ... );     // A. Create the initialize the rotating ladder     ...     // B. Create and initialize the bouncing soccer ball     ...     // C. Create and initialize the cicle controlled by the right thumb stick     ...     // D. Create and initialize the eraser Rectangle     ...     // E. Insert: RightThumbCircle, and Ladder into the m_VisibleSet     m_VisibleSet = new XNACS1 PrimitiveSet ();     m_VisibleSet.AddToSet(m_RightThumbCircle);     m_VisibleSet.AddToSet(m_RotatingLadder);     m_SetISVisible = true ; }

At label E , after allocating the memory for the m_VisibleSet , we inserted the RightThumbCircle and the RotatingLadder to be members of the m_VisibleSet , and record the fact that current the m_VisibleSet is visible by setting m_SetIsVisibl e to true.

6. Examine UpdateWorld() function of Game1.cs

Now in the UpdateWorld() function, we control the visibility of the m_VisibleSet and the speed of the soccer ball after collision:

protected override void UpdateWorld() {   if (GamePad.ButtonBackClicked())       this .Exit();  #region  A. Update the Rotating ladder      ...       #region B. ...   #region C. ...  #region D. ...  # region E. toggle VisibleSet by the X-Button      if (GamePad.ButtonXClicked()) {            if (m_SetIsVisible)                 m_VisibleSet.RemoveAllFromAutoDrawSet();           else                 m_VisibleSet.AddAllToAutoDrawSet();           m_SetIsVisible = !m_SetIsVisible;      }    #endregion   # region F. Collide the soccer with the rotating ladder      bool collided = m_SoccerBall.Collided(m_RotatingLadder);     if (collided) {         m_SoccerBall.VelocityDirection = m_SoccerBall.Center - m_RotatingLadder.Center;         m_SoccerBall.Speed = SPEED * RandomFloat(0.5f, 2.0f) ;     }     ...  #endregion  EchoToTopStatus(...); }

• Region E: When the X-Button is clicked, we check if m_SetISVisible , if so, we "RemoveAllFromAutoDrawSet()" to hide the RightThumbCircle and the Ladder. Otherwise we call "AddAllToAutoDrawSet()" to show the two primitives.
  
• Region F: When collision between the soccer and the ladder is detected, the speed of the soccer is randomized by the "RandomFloat()" function.

	This work is supported in part by a grant from Microsoft Research under the Computer Gaming Curriculum in Computer Science RFP, Award Number 15871 and 16531.
2/8/2010