Gaming Introduction

Video games have been an important part of computer systems since their early days. We will start by making the simplest possible video game.

Prerequisite

You must have a basic understanding of coding and have completed the Drawing lesson.

Game Objective

The player will need to catch falling eggs in a basket. For simplicity, the eggs are just a circle and the basket is just a rectangle.

Basket Drawing

The player, which is a basket in this case, is just a Line(), or we can use FillRect() to make a thicker line.

LcdClear(0)
LcdRect(1,10,60,20,3)
LcdShow()

Basket Control

Buttons A and B will be used to control the player (basket). Instead of using the BtnDown() function, we will use DRead(). This is because we will need to know if the button is constantly down vs reading a button click. The B variable will be used for the basket’s position. We can create a subroutine that processes the basket.

@Basket
    If DRead('A',1) = 0
        b = b - 6
    End
    If DRead('B',1) = 0
        b = b + 6
    End
    LcdRect(1,b,60,20,3)
Return

With the basket process in place, we can now create the game loop, to process and draw the “basket”. The following code to the top of the program

@Loop
    LcdClear(0)
    Basket()
    LcdShow()
Goto Loop

The entire code listing is here in case you have missed something.

b=20
@Loop
    LcdClear(0)
    Basket()
    LcdShow()
Goto Loop

@Basket
    If DRead('A',1) = 0
        b = b - 6
    End
    If DRead('B',1) = 0
        b = b + 6
    End
    LcdRect(1,b,60,20,3)
Return

Try what we have so far. Did you notice how the basket can leave the screen if you keep pushing one of the buttons? Any ideas on how we can keep the basket from leaving the screen?

Stay on Screen

Keeping the basket on the screen is somewhat easy. We will check the basket’s position and only change its position if the buttons are pressed and also if the basket is not leaving the screen. Notice how we used “and” in the previous sentence. The code will also be exactly just that.

Can you see why we did 128-20?

@Basket
    If DRead('A',1) = 0
        b = b - 6
    End
    If DRead('B',1) = 0
        b = b + 6
    End
    If b<0:b=0:End
    If b>(128-20):b=128-20:End
    LcdRect(1,b,60,20,3)
Return

Falling Eggs

We’ll use a Circle() as our egg with its location being X and Y. We will add a subroutine to process the egg. This can then be added to the main game loop.

@Egg
    y = y + 3 # The egg is falling
    if y>63 # Did the egg reach the bottom?
        y=0 #move the Egg back to the top
    End
    LcdCircle(1,x,y,3)
Return

The eggs will always start on top of the screen and fall down. The “down movement” means the Y axis location will increase. Remember, the top of the screen is 0. Y variable will keep track of the ball position falling down.

For the X axis position, we will use X variable. Let us just set it and keep it at 20 for now. Here is the full code listing.

x=20 # just for now
@Loop
    LcdClear(0)
    Basket()
    Egg()
    LcdShow()
Goto Loop

@Basket
    If DRead('A',1) = 0
        b = b - 6
    End
    If DRead('B',1) = 0
        b = b + 6
    End
    If b<0:b=0:End
    If b>(128-20):b=128-20:End
    LcdRect(1,b,60,20,3)
Return

@Egg
    y = y + 3 # The egg is falling
    if y>63 # Did the egg reach the bottom?
        y=0 #move the Egg back to the top
    End
    LcdCircle(1,x,y,3)
Return

That is starting to look like a game. We now need to change where the egg falls down from. We want it coming down from a random location. Thankfully, the random is a built-in feature in most programming languages.

@Egg
    y = y + 3 # The egg is falling
    if y>63 # Did the egg reach the bottom?
        y=0 #move the Egg back to the top
    End
    x = Rnd(128)
    LcdCircle(1,x,y,3)
Return

Keeping Score

The basket is moving and the egg is falling but where is the score? This is done by comparing the position of the egg to the basket. We only need to do this when the egg reaches the bottom. If the egg is within the basket, we will increase the score (variable s) by one.

@Egg
    y = y + 3 # The egg is falling
    If y>63 # Did the egg reach the bottom?
        y=0 #move the Egg back to the top
        If (x > b) && (x < (b+10))
            s = s + 1
        End
    End
    x = Rnd(128)
    LcdCircle(1,x,y,3)
Return

We finally can show off our score! Let’s place it in the top left corner.

@Loop
    LcdClear(0)
    Basket()
    Egg()
    LcdText(Str(s),1, 2, 2)
    LcdShow()
Goto Loop

Final Results

A playable game with under 30 lines of code! Not bad considering commercial games are usually thousands or millions of lines of code. Here is the complete code with all the parts we’ve shown above:

b=50
@Loop
    LcdClear(0)
    Basket()
    Egg()
    LcdText(Str(s),1, 2, 2)
    LcdShow()
Goto Loop
@Basket
    If DRead('A',1) = 0
        b = b - 6
    End
    If DRead('B',1) = 0
        b = b + 6
    End
    If b<0:b=0:End
    If b>(128-20):b=128-20:End
    LcdRect(1,b,60,20,3)
Return
@Egg
    y = y + 3 # The egg is falling
    If y>63 # Did the egg reach the bottom?
        y=0 #move the Egg back to the top
        x = Rnd(128)
        If (x > b) && (x < (b+10))
            s = s + 1
        End
    End
    LcdCircle(1,x,y,3)
Return

What is Next?

Dig deeper into code and build a Brix game.

BrainStorm

Do video games really detect collisions properly? Or is it just checking for location? Things get more advanced in 3D space and advanced computing but will the answer be going the easy route? What about “falling” objects? Did we do proper gravity physics calculations? It was a simple addition. Can you think of video games where proper physics calculations are a must?

DUE Gaming Intro