Space Fighter (a complete game & DirectDraw Tutorial)

<font face="Arial" size="2">A complete DirectDraw Game & 
Tutorial</font></p>
<p align="left"><font face="Arial" size="2">        
To skip to the tutorial, <a href="#DirectDraw Tutorial">click here</a>. <br>        
To skip to the bonus content, <a href="#Bonus Content.">click here</a>.<br>        If you are interested in another 
tutorial in DirectDraw, made by me, you can check out the
<a href="http://www.pscode.com/vb/scripts/ShowCode.asp?txtCodeId=36204&lngWId=1">
PingBall Challenge</a>, the same type of tutorial: you get a game, rules, and an 
instruction on how to make it.</font></p>
<p align="left"><font face="Westminster" size="6">   
<a name="Space Fighter Challenge.">Space Fighter Challenge.</a></font><br>        Well... here goes the 
second one. Finish at least 20 levels of this game. You control a ship which has 
got 100 health points. When you are hit with a laser, you lose 1 health point. 
If you hit another ship (!!!), you lose 10 health points.<br>        Your health points 
are restored every time you enter a new level. You will enter level 2 on 100 
points, level 3 on 200 points, level 4 on 400 points. To calculate the  
amount of points needed to enter a level you can use this formula: amount=100*2^LevelToEnter 
.<br>        You are apposed by a 
small (you will see just how <i>small</i> it is, when you reach higher levels) 
fleet of ships. As you progress in levels, the AI on those ships will improve. 
So will the health points.<br>        You can use any kind 
of strategy you like, it all is quite difficult. <b>Post your scores here</b>, 
and may the <b>best one win!</b></p>
<p align="left"><font face="Westminster" size="6">   
<a name="DirectDraw Tutorial">DirectDraw Tutorial</a></font><br>
<font face="Arial" size="2">        Unlike 
the PingBall Challenge, this one doesn't contain any resolution code. So, if the 
game runs slow, decrease the resolution. Please do not decrease the color depth 
to anything lower than 16-bit - it makes it look <i>bad</i>.</font></p>
<p align="left"><font face="Arial" size="2">        
The program starts with the Form_Load event, in which the mouse is immediately 
hidden (thanks, Mick!), and then it does to the Init sub.</font></p>
<p align="left"><font face="Arial" size="2">        
The Init sub is the core of the whole program: it initializes, and runs the game 
(or maybe calls the subs that run the game). First (after setting the error 
handler), we create DirectDraw, and bind it to our form (<i>Call 
dd.SetCooperativeLevel(Me.hWnd, DDSCL_FULLSCREEN Or DDSCL_ALLOWMODEX Or 
DDSCL_EXCLUSIVE)</i>). Then we <i>SetDisplayMode </i>to 800x600 with 16-bit 
depth - 65025 colors. After creating the <i>description</i> of the primary 
surface, we create the primary surface from it. The back buffer is then created 
for the primary buffer.</font></p>
<p align="left"><font face="Arial" size="2">        
Those who know the basic concepts of DirectDraw, are recommended to 
<a href="#Then comes">click here</a> 
(skips a few paragraphs). However, you might just read on.</font></p>
<p align="left"><font face="Arial" size="2">        
The primary surface represents the screen. Everything that appears on the 
primary surface, appears on screen. Now, if I was to paint the whole thing 
directly on the primary surface, the one playing the game would see me painting, 
and (probably) the screen will flicker. To counter this, people use backbuffers. 
When you paint onto the backbuffer, user doesn't see anything. Then, in one 
action (<i>Flip</i>), you paint the entire scene onto the primary surface - the 
user doesn't see you painting.</font></p>
<p align="left"><font face="Arial" size="2">        
Imagine a surface as an image. You can print the text on (only it's not called 
printing), or put additional pictures. DirectDraw makes it fast and quick, and 
adds some features. For example, very easy transparency. Matt Carpenter's
<a href="http://www.pscode.com/vb/scripts/ShowCode.asp?txtCodeId=36283&lngWId=1">
A Cool Space Invaders Game</a> uses masks to achieve this. It's painful, and you 
have to store the masks somewhere as well. To see how I solve this problem, read 
on.</font></p>
<p align="left"><font face="Arial" size="2">        
Then, to load an image, you need to describe it first. You will need to set it's 
height & width, before you can load it. </font></p>
<p align="left"><font face="Arial" size="2">        
<a name="Then comes">Then comes</a> the first real code: you have to load the images. <b>COPY CODE:</b> 
you might want to use <b>UniversalLoad</b> in your programs. Since DirectDraw 
understands only bitmap images, we will have to re-save the file as bitmap if it 
isn't already. The sub is quite self-explanatory. The flags I use are standard, 
and you know them from their name. What I do in the end is that I define that 
the black color shouldn't be blitted, when a special flag is used. That is the 
first half of the transparency</font></p>
<p align="left"><font face="Arial" size="2">        
All the small things done (such as creating the starry background, initializing 
the arrays, fonts), we get onto our 5 line program : </font></p>
<p align="left"><b><font face="Arial" size="2">Do </font><br><b><font face="Arial" size="2">SplashEngine</font><br>
<font face="Arial" size="2">StoryEngine</font><br>
<font face="Arial" size="2">GameEngine</font><br>
<font face="Arial" size="2">Loop</font></b></p>
</b>
<p align="left"><font face="Arial" size="2">        
You can see that the whole program is done in Engine subs. Each Engine sub does 
it's own things, and is accompanied by a Blt sub with the same first part of the 
name.</font></p>
<p align="left"><font face="Arial" size="2">       
<b>SplashEngine</b> just scrolls the star field, and displays your ship in the 
center. Blt sub does this: empties the screen (<i>BltColorFill</i>), and prints 
the text. Notice the <i>DDBLTFAST_SRCCOLORKEY</i> flag in the blt sub - it makes 
sure that we use the color key that we defined in the InitSurfaces sub - second 
part of my transparency. And, this is minimal trouble, and almost no performance 
decrease.</font></p>
<p align="left"><font face="Arial" size="2">       
<b>StoryEngine</b> controls the small story that we have along with the game - 
it calls the SplashBlt sub with the text it wants to display.</font></p>
<p align="left"><font face="Arial" size="2">       
<b>GameEngine</b> is the core of the game (again!). It calls (again!) the 
different subs that drive the game. Let's take a look at those one by one.</font></p>
<p align="left"><font face="Arial" size="2">       
<b>CheckLevel</b> makes sure that we are on the correct level. It is basic and 
self-explanatory.</font></p>
<p align="left"><font face="Arial" size="2">       
<b>StarFieldProccess</b> take every star, and moves it by it's SpeedY. It also 
re-spawns the stars when they meet the bottom. Very basic.</font></p>
<p align="left"><font face="Arial" size="2">       
<b>MoveYourShip</b> is responsive for controlling the movement of your ship (how 
did you guess?). It takes the SpeedX (and SpeedY if a certain constant is true, 
about that later), adds it, and then handles the consequences.</font></p>
<p align="left"><font face="Arial" size="2">       
<b>MoveAIUnits</b> is a more complex part. It is a loop to call <i>EnemyAI</i> 
for every enemy, and to re-spawn the enemies when they are killed or hit the 
bottom.<br>       
<b>    EnemyAI</b> is passed with an enemy ID, and enemy's AI 
level (1-100). It is responsible for what each ship does. Basically, it's a 
large Select Case, which then uses <i>enemy(ID).location</i> and <i>yourlocation</i> 
to compute what it should do. It's easy to figure out what it does, and there is 
nothing special to DirectDraw here</font></p>
<p align="left"><font face="Arial" size="2">       
<b>HandleBullets </b>is probably the most severe computing sub in the entire 
game. It checks who wants to shoot, checks whether they can shoot, and shoots 
(if they can). It handles both AI and Player actions. It uses <i>BadWeaponShots
</i>and <i>GoodWeaponShots</i> to store the coordinates of the laser shots.<br>
        
Every time it's called, it cleans-up it's old bullets, not to waste memory. Then 
it uses <i>Collides</i> function to determine the collisions between laser shots 
and targets. It does that for both sides. It also handles the damage done by 
this shot. Then, (as a bonus) it checks for collisions between your ship and 
enemy ships.<br>       
<b>Collides</b> is a sub that <b>You can copy</b>, and use in your own projects. 
It checks if the figure1 collides with figure2 - a sort of collision detection 
sub. I think it's correct, at least 90% of this game relies on it..</font></p>
<p align="left"><font face="Arial" size="2">       
<b>Gameblt</b>, finally, is the sub that paints it all. This one is quite 
complex so let's walk through it.<br>       
<b>CheckScreen</b> <b>(Copy Code: CheckScreen, ExModeActive</b>, and 
adjust the name of the sub that should be called to restore the surfaces) )is a 
standard sub in any blt sub I wrote - it checks if the user hadn't switched away 
from us (ALT-TAB or CTRL-ALT-DEL). If the user didn't, nothing happens. However, 
if he/she did, the sub would be in the loop until he switches back. It then 
would restore the surfaces.<br>       
<b>BltColorFill</b> just blanks the entire screen with black color.<br>       
<b>StarFieldToBackBuffer</b></font> just paints the stars() array to the back 
buffer. Simple. It uses the star surface to create them (<i>BltFast</i>) on the 
screen.<br>        Then it paints all 
the standard text onto the top left corner.<br>        Then, using loops, it 
paints Enemy ships, your laser shots, and enemy laser shots. If the <b>loss</b> 
variable is not true, it paints your ship. If it is, it paints the You Lost! 
message. Then the whole thing is <i>Flip</i>ed onto the primary surface. That is 
it.</p>
<p align="left">        If you want to skip 
this, <a href="#So, how does">click here.</a></p>
<p align="left">        <b>On Blitting</b>. 
There is a number of different Blt subs used by DirectDraw. </p>
<blockquote>
 <ul>
 <li>
 <p align="left">Blt allows you to strech what you are drawing. It is a 
 little slower then (next one)</li>
 <li>
 <p align="left">BltFast - supply the x,y coordinates, plus a rectangle - and 
 it paints. It's faster.</li>
 <li>
 <p align="left">BltColorFill - doesn't paint an image, just a huge box 
 filled with the color you specify.</li>
 <li>
 <p align="left">There are other blts, but they are little or no use in the 
 scope of this tutorial.</li>
 </ul>
 <p align="left"><b>On RECT</b>.</p>
</blockquote>
<p align="left">        You select which part 
of the picture you want copied/copied to. In our case, we want the whole 
picture, so we can just forget about modifying this, and just pass it as it is. 
If you want to use it, set Left and Top as you would normally, while Right 
should be Left + Width, Bottom should be Top + Height.</p>
<p align="left">       
<a name="So, how does">So, how does</a> this thing work? It is tied together by 
the Form_Keydown and Form_KeyUp events. Keydown basically provides control of 
the game - it allows you to pause, start or end the game, as well as checking 
your Left & Right arrows (Up & Down ones as well...), Space, and other keys. It 
sets variables that can be used, if the Engine running is right. Otherwise, they 
are just ignored.</p>
<p align="left"><font face="Westminster" size="6">   
<a name="Bonus Content.">Bonus Content.</a></font></p>
<p align="left"><font face="Arial" size="2">        
Bonuses? Quite a few actually. Check the ModTypes for the declarations of 
various constants are used. Most of the bonuses are achieved by changing these. 
Let's take them one by one:<br>
 <ul>
 <li>
 <b>AllowYMovement</b> - if true, 
 it allows you to use Up & Down arrows to move vertically. Recommended: 
 False.</li>
 <li>
 <b>AmountOfStars</b> - specifies how many stars are there in the background. 
 You can increase the setting if you want a more starry background, or would 
 like to slow down (for some reason) the game.<li>
 <b>MaxStarSpeed</b> - specifies the maximum speed with which a star should 
 move. Larger numbers will be uncomfortable.<li>
 <b>MaxGoodBullets</b> - the maximum amount of your shots that can be in the 
 air at once. You can lower this value if you want a more challenging game.<li>
 <b>MaxBadBullets</b> - the maximum amount of bad shots that cen be in the air 
 at once. You can lower the value to make it easier on higher levels, or put it 
 sky-high to  have certain death on lvl 55.</ul>
<p></p>
<p></p>
<p></p>
<p></p>
<p></p>
<p>         That's about it. Thanks for 
reading this far. If you liked it, vote.</p>
</font><font face="Arial" size="4">
<p align="center"><b>The END</b></p>