Software Design Using C++

Beginner-Level GDK Capstone Programs

Overview

Thus far in our tutorials utilizing Dark GDK, we have attempted to present programs which have direct relevance to the lessons with which they are associated. Now, as we approach the end of our beginning tutorials it seems appropriate that we should have at least a few unrelated programs, just as we looked at some introductory material at the beginning of the lessons. We will consider two simple programs which combine a variety of what we have done this semester without exhausting it, however. As we continue through the intermediary material and the advanced material, our creations will be of far greater complexity than these simple programs.

Nevertheless, let us go off the beaten path to look at two final edifying example programs.

Simple Asteroid Avoiding Game

What would be 2D graphics programming without something like a moving sprite on the screen, controlled by the user? Better yet, what would it be without having to avoid asteroids? Well, we're not going to look at the case of the plural if for no reason than to keep the complexity of the program down for these tutorials. However, we will now look at a little game which draws a spaceship on the screen as well as an asteroid which begins moving in a random direction. The code is available at MovingSprite.cpp.

Most of our initialization protocol is the same. There is one new function which is called at the beginning after everything has been initialized, namely dbRotateSprite. Since this function will play a role below, we will consider it now. Simply put this function rotates a given sprite, identified by the first parameter by a given amount of degrees in the clock-wise direction. Every sprite is rendered with an initial "direction" which is rotated in addition to the image. Initially, the direction is upward which is defined by the normalized 2-dimensional vector <0,-1>, having no x component and a negative y component. As we rotate the sprite, this direction is rotated too. When we call the dbMoveSprite function, we move the sprite which is specified by the first parameter by the distance indicated by the second parameter, in the current forward direction of the sprite. The reason that we rotate the asteroid by a random amount is to give it a random direction to fly through the space setting.

The only really substantial section in this code is the main event loop:

while(LoopGDK() && !dbSpriteHit (2,3)) {
   // Check for forward / backward thrust
   if(dbUpKey()) {
	  dbMoveSprite(2,spriteVelocity);
   } else if (dbDownKey()) {
	  dbMoveSprite(2,-spriteVelocity);
   }

   // Check for rotation
   if(dbLeftKey()) {
	  spriteAngle -= spriteRotationAmount;
	  dbRotateSprite(2,spriteAngle);
   } else if(dbRightKey()) {
	  spriteAngle += spriteRotationAmount;
	  dbRotateSprite(2,spriteAngle);
   }
   dbMoveSprite(3,asteroidVelocity);
   // See if the sprites went off the screen and act appropriately
   spriteWrapAround(2);
   spriteWrapAround(3);
   dbSync();
}

There are many ways by which you could extend this program, though I leave that in your hands, since we will revisit this in the intermediate section of the book to add various features based on the lesson contents. The whole program and its dependent files can be found at in MovingSprite.zip.

Mouse Input

Our final example is one which uses mouse input, MouseInput.cpp. Also, you may want to save drawing.txt to the executing directory for your program. You will see the role of this file as we discuss this example. This should remind you of the work we did in ShapeLoader.cpp and CreateShapeFile.cpp with a deal more interactivity! First, we should lay out the overall flow of the program logic:

fstream OutFile;

...

// Perform necessary start files
if(!loadFileContents())
{
  dbPrint("Failed to load save-state file!\nPress any key to terminate program.");
  dbWaitKey();
  return;
}

OutFile.open(DRAWING_FILE_NAME,ios::app);

if(OutFile.fail()) {
  dbPrint("Failed to open save-state file!\nPress any key to terminate program.");
  dbWaitKey();
  return;
}

Next, we have the main event loop:

// Main event loop
while(LoopGDK())
{
  // Check to see if the space bar has been pressed (to indicate a screen clear)
  if(dbSpaceKey()) 
  {
	 dbCLS();
	 OutFile.close();
	 OutFile.open(DRAWING_FILE_NAME,ios::out);
	 if(OutFile.fail()) {
		dbPrint("File Error! Aborting!\nPress any key to terminate program.");
		dbWaitKey();
		return;
	 }
  }
  
  // Get mouse information
  mouseButtonNum = dbMouseClick();
  mouseX = dbMouseX();
  mouseY = dbMouseY();
  
  // Decide if the shape will be filled
  filled = dbControlKey();
  
  // Check to see if any buttons are down
  if(mouseButtonNum == 1)
  {
	 performRectangle(mouseX,mouseY,filled,OutFile);
	 // A rather primitive way to wait for the left button to come up
	 // without using threads
	 while(dbMouseClick() == 1);
  }
  else if(mouseButtonNum == 2)
  {
	 performCircle(mouseX,mouseY,filled,OutFile);
	 // A rather primitive way to wait for the left button to come up
	 // without using threads
	 while(dbMouseClick() == 2);
  }
  
  // Wait a millisecond to keep from locking up with a fast-executing loop
  dbWait(1);
}

Conclusion

We have covered some ground in this first course, though there is much more that we can do in the coming two sets of sections. Learn these concepts thoroughly because we will pick up exactly where we have left off, plowing forward in the next section of this text. Perhaps you can think of some ways to modify these files. That would make for a great tool in deeply learning to use the toolkit.