Jeff Molofee - NeHe's OpenGL Tutorials

We start off by checking to make sure the game isn't over, and that the window (if in windowed mode) is still active. By checking active the enemies wont move if the screen is minimized. This gives you a convenient pause feature when you need to take a break :)

After we've made sure the enemies should be moving, we create a loop. The loop will loop through all the visible enemies. Again we calculate how many enemies should be on the screen by multiplying the current stage by the current internal level.

if (!gameover && active) // If Game Isn't Over And Programs Active Move Objects

{

for (loop1=0; loop1<(stage*level); loop1++) // Loop Through The Different Stages

{

Now we move the current enemy (enemy[loop1]). We start off by checking to see if the enemy's x position is less than the players x position and we make sure that the enemy's fine y position lines up with a horizontal line. We can't move the enemy left and right if it's not on a horizontal line. If we did, the enemy would cut right through the middle of the boxes, making the game even more difficult :)

If the enemy x position is less than the player x position, and the enemy's fine y position is lined up with a horizontal line, we move the enemy x position one block closer to the current player position.

We also do this to move the enemy left, down and up. When moving up and down, we need to make sure the enemy's fine x position lines up with a vertical line. We don't want the enemy cutting through the top or bottom of a box.

Note: changing the enemies x and y positions doesn't move the enemy on the screen. Remember that when we drew the enemies we used the fine positions to place the enemies on the screen. Changing the x and y positions just tells our program where we WANT the enemies to move.

if ((enemy[loop1].x

enemy[loop1].x++; // Move The Enemy Right

}

if ((enemy[loop1].x>player.x) && (enemy[loop1].fy==enemy[loop1].y*40)) {

enemy[loop1].x--; // Move The Enemy Left

}

if ((enemy[loop1].y

enemy[loop1].y++; // Move The Enemy Down

}

if ((enemy[loop1].y>player.y) && (enemy[loop1].fx==enemy[loop1].x*60)) {

enemy[loop1].y--; // Move The Enemy Up

}

This code does the actual moving. We check to see if the variable delay is greater than 3 minus the current internal level. That way if our current level is 1 the program will loop through 2 (3-1) times before the enemies actually move. On level 3 (the highest value that level can be) the enemies will move the same speed as the player (no delays). We also make sure that hourglass.fx isn't the same as 2. Remember, if hourglass.fx is equal to 2, that means the player has touched the hourglass. Meaning the enemies shouldn't be moving.

If delay is greater than 3-level and the player hasn't touched the hourglass, we move the enemies by adjusting the enemy fine positions (fx and fy). The first thing we do is set delay back to 0 so that we can start the delay counter again. Then we set up a loop that loops through all the visible enemies (stage times level).

if (delay>(3-level) && (hourglass.fx!=2)) // If Our Delay Is Done And Player Doesn't Have Hourglass

{

delay=0; // Reset The Delay Counter Back To Zero

for (loop2=0; loop2<(stage*level); loop2++) // Loop Through All The Enemies

{

To move the enemies we check to see if the current enemy (enemy[loop2]) needs to move in a specific direction to move towards the enemy x and y position we want. In the first line below we check to see if the enemy fine position on the x-axis is less than the desired x position times 60. (remember each grid crossing is 60 pixels apart from left to right). If the fine x position is less than the enemy x position times 60 we move the enemy to the right by steps[adjust] (the speed our game is set to play at based on the value of adjust). We also rotate the enemy clockwise to make it look like it's rolling to the right. We do this by increasing enemy[loop2].spin by steps[adjust] (the current game speed based on adjust).

We then check to see if the enemy fx value is greater than the enemy x position times 60 and if so, we move the enemy left and spin the enemy left.

We do the same when moving the enemy up and down. If the enemy y position is less than the enemy fy position times 40 (40 pixels between grid points up and down) we increase the enemy fy position, and rotate the enemy to make it look like it's rolling downwards. Lastly if the enemy y position is greater than the enemy fy position times 40 we decrease the value of fy to move the enemy upward. Again, the enemy spins to make it look like it's rolling upward.

if (enemy[loop2].fx

{

enemy[loop2].fx+=steps[adjust]; // If So, Increase Fine Position On X Axis

enemy[loop2].spin+=steps[adjust]; // Spin Enemy Clockwise

}

if (enemy[loop2].fx>enemy[loop2].x*60) // Is Fine Position On X Axis Higher Than Intended Position?

{

enemy[loop2].fx-=steps[adjust]; // If So, Decrease Fine Position On X Axis

enemy[loop2].spin-=steps[adjust]; // Spin Enemy Counter Clockwise

}

if (enemy[loop2].fy

{

enemy[loop2].fy+=steps[adjust]; // If So, Increase Fine Position On Y Axis

enemy[loop2].spin+=steps[adjust]; // Spin Enemy Clockwise

}

if (enemy[loop2].fy>enemy[loop2].y*40) // Is Fine Position On Y Axis Higher Than Intended Position?

{

enemy[loop2].fy-=steps[adjust]; // If So, Decrease Fine Position On Y Axis

enemy[loop2].spin-=steps[adjust]; // Spin Enemy Counter Clockwise

}

}

}

After moving the enemies we check to see if any of them have hit the player. We want accuracy so we compare the enemy fine positions with the player fine positions. If the enemy fx position equals the player fx position and the enemy fy position equals the player fy position the player is DEAD :)

If the player is dead, we decrease lives. Then we check to make sure the player isn't out of lives by checking to see if lives equals 0. If lives does equal zero, we set gameover to TRUE.

We then reset our objects by calling ResetObjects(), and play the death sound.

Sound is new in this tutorial. I've decided to use the most basic sound routine available… PlaySound(). PlaySound() takes three parameters. First we give it the name of the file we want to play. In this case we want it to play the Die .WAV file in the Data directory. The second parameter can be ignored. We'll set it to NULL. The third parameter is the flag for playing the sound. The two most common flags are: SND_SYNC which stops everything else until the sound is done playing, and SND_ASYNC, which plays the sound, but doesn't stop the program from running. We want a little delay after the player dies so we use SND_SYNC. Pretty easy!

The one thing I forgot to mention at the beginning of the program: In order for PlaySound() and the timer to work, you have to include the WINMM.LIB file under PROJECT / SETTINGS / LINK in Visual C++. Winmm.lib is the Windows Multimedia Library. If you don't include this library, you will get error messages when you try to compile the program.

// Are Any Of The Enemies On Top Of The Player?

if ((enemy[loop1].fx==player.fx) && (enemy[loop1].fy==player.fy)) {

lives--; // If So, Player Loses A Life