Zap Game: Closer Look at for loop counter

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:
  • Examine how to use a for loop that isn't strictly a counting loop

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 almost identically to the prior version, which was explained in the 305 tutorial .  The only visible change is that instead of having a single, continuous beam that the player uses to try and zap the enemy, there is now a line of distinct dots, as pictured above.

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

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

  Version of code in 305 tutorial	Version of code in this tutorial
  XNACS1Circle lastCircle = null ; Vector2 HeroBeam = m_Hero.Center; for (float x = m_Hero.CenterX+1; x < m_Enemy.CenterX ; x++ ) {     HeroBeam.X = x;     lastCircle = CreateHeroPath(HeroBeam); }	XNACS1Circle lastCircle = null ; Vector2 HeroBeam = m_Hero.Center; for (float x = m_Hero.CenterX+1; x < m_Enemy.CenterX; x+=(3*HERO_PATH_SIZE ) ) {     HeroBeam.X = x;     lastCircle = CreateHeroPath(HeroBeam); }

  • In order to emphasize the differences between the code provided in the 305 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.
  • Notice that in this tutorial, we're using a for loop to control the placement of the circles that making up the hero's laser beam, but instead of using a simple counting loop (wherein x is incremented or decremented by one in each iteration of the loop), we're using a (slightly) different loop, that will increase x by three times as much as the HERO_PATH_SIZE (which is defined as a constant, above - it's the size of each of the circles in the laser beam).

FURTHER EXERCISES::  

1. Something

	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