Zap Game: Nesting While and For Loops

References:

• Pre-requisite: it is assumed that you have read through the prior tutorials, and are familiar with the concepts covered in those tutorials.

Goals:

• In this tutorial, we will:
  • Different kinds of nested loops for Hero zap path to skip the blocks: line 159

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 .

When the game starts, you'll see a screen that looks similar to this:

This version of the 'zap' game looks and plays very similarly to the prior version, which was explained in the 405 tutorial .  The major change in this version is that the game will detect when the player's zapping beam has collided with any of the three blocks, and will cause the laser beam to around each block before continuing on towards the enemy, as pictured above.  The enemy's laser beam is still stopped by the first block it hits

2. Examining The Program:

Let's examine the C# source code that produces the behavior we see on-screen

• Generating the Hero's Laser in UpdateWorld():

  Version of code in 405 tutorial

  Version of code in this tutorial

  for (float x = m_Hero.CenterX + 1; x < m_Enemy.CenterX; x += HERO_PATH_SIZE) {     HeroBeam.X = x;     lastCircle = CreateHeroPath(HeroBeam);       if (lastCircle.Collided(m_BlockA))     {         for (float y = HeroBeam.Y + 1; y <= m_BlockA.MaxBound.Y; y++)         {             HeroBeam.Y = y;             lastCircle = CreateHeroPath(HeroBeam);         }     } }

  for (float x = m_Hero.CenterX + 1; x < m_Enemy.CenterX; x += HERO_PATH_SIZE) {     HeroBeam.X = x;     lastCircle = CreateHeroPath(HeroBeam);       if (lastCircle.Collided(m_BlockA))     {         for (float y = HeroBeam.Y + 1; y <= m_BlockA.MaxBound.Y; y++)         {             HeroBeam.Y = y;             lastCircle = CreateHeroPath(HeroBeam);         }     }     else if (m_BlockB.Collided(lastCircle))     {         float steps = HeroBeam.Y - m_BlockB.MinBound.Y;         for ( int dy = 1; dy < steps; dy++)         {             Vector2 newPos = HeroBeam;             newPos.Y -= dy;             lastCircle = CreateHeroPath(newPos);         }         HeroBeam.Y -= steps;     }     else if (m_BlockC.Collided(lastCircle))     {         while (HeroBeam.Y < m_BlockC.MaxBound.Y)         {             HeroBeam.Y += 1f;             lastCircle = CreateHeroPath(HeroBeam);         }     } }

  • In order to emphasize the differences between the code provided in the 405 tutorial and the code provided in this tutorial, we have aligned the loop from the 'hero zapping' region side-by-side, with the new loop in this tutorial on the right.
  • You'll notice that nothing has been changed or removed from the prior version - the only difference is that we have added two new, inner, nested loops.  The first loop handles the case where the laser beam has collided with the 'B' block - in this case, the laser beam runs down the block (because of the newPos.Y -= dy; line ).  The third block is almost identical to the first block, except that it handles the case where the laser collides with the 'C' block - in this case, the laser runs up the block.

FURTHER EXERCISES::  

1. Rework the enemy's zapping code so that the enemy's laser, just like the hero's laser, slides around the different blocks.
2. Rework the above code so that if the hero's laser collides with the top half of a given block, the laser will go up the block, and if the laser collides with the bottom half (or middle) of the block, the laser will slide down the block
   1. Do the same thing for the enemy's laser.

	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