RIGHT = 1
DOWN = 2
LEFT = 3
MAX_LENGTH = 256
OBJ
lcd : "LameLCD"Instructions
Maximum snake!
We need to define an array, but first, let’s add a constant for the maximum number of snakes. This is important, because without it, it’s chaos trying to remember how many are allowed throughout your program.
First, decide how long the snake can be. We need to know how big to make the arrays. 256 seems pretty big, but on a 128x64 screen, there are 8192 pixels!
Snake.spin
We need to turn our snakex and snakey variables into arrays.
Snake.spin
ctrl : "LameControl"
VAR
byte snakex[MAX_LENGTH]
byte snakey[MAX_LENGTH]
byte snakedirWe now need to update the syntax of every snakex and snakey. Find (Ctrl+F) is the fastest way to make this happen.
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Warning
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Make sure you replace all instances of Don’t accidentally replace your array declaration: |
How much is too much?
Since the snake starts small and grows, we also need to keep track of how many snake dots there are on the screen at any time. So we’ll create snakecount. Byte-sized is fine, since MAX_LENGTH is 256.
Snake.spin
VAR
byte snakex[MAX_LENGTH]
byte snakey[MAX_LENGTH]
byte snakedir
byte snakecount
PUB Main
lcd.Start(gfx.Start)Since we start with 1 pixel, we’ll set snakecount to 1 at startup.
Snake.spin
snakey[0] := 32
snakedir := 1
snakecount := 1
repeat
gfx.ClearWe’re going to add a variable i. This one is just used for a repeat loop.
Snake.spin
byte snakedir
byte snakecount
byte i
PUB Main
lcd.Start(gfx.Start)Lining them up
What we need to do is make each and every dot follow the one that came before it in a line. That’s easy enough. The position of the next position should equal the position of the last.
Snake.spin
snakex[i] := snakex[i-1]So how do we go over all the points of the snake so that this will work? There’s two options:
Option 1: Front to back
We start from the front of the snake and go to the end.
repeat i from 1 to snakecount
If we run these commands in order:
snakex[1] = snakex[0] snakex[2] = snakex[1] snakex[3] = snakex[2]
This doesn’t work. When you simplify it, you end up with this:
snakex[3] = snakex[2] = snakex[1] = snakex[0]
In other words, a single dot. Lame.
Option 2: Back to front
We can also try starting from the back of the snake and going to the front.
repeat i from snakecount to 1
You’ll see that running it this way yields the result we want.
snakex[3] = snakex[2] snakex[2] = snakex[1] snakex[1] = snakex[0]
In other words, snakex[3] is the old value of snakex[2], snakex[2] is the old value of snakex[1], and snakex[1] is the old value of snakex[0].
Well, gee, that’s just what we want!
There is only one value that isn’t set this way, and that’s snakex[0]. That’s okay though, because we already set snakex[0] via player direction.
Here’s the code that calculates the locations of the snake’s tail. We should place this code after drawing the first snake sprite but before lcd.Draw.
Snake.spin
if snakedir == DOWN and snakey[0] < constant(64-2)
snakey[0]++
gfx.Sprite(@dot_gfx, snakex[0], snakey[0], 0)
repeat i from snakecount to 1
snakex[i] := snakex[i-1]
snakey[i] := snakey[i-1]
lcd.Draw
DAT
dot_gfxDon’t forget, though. We also want to see the tail, so make sure to include a call to gfx.Sprite to draw the tail at each position.
Snake.spin
gfx.Sprite(@dot_gfx, snakex[0], snakey[0], 0)
repeat i from snakecount to 1
snakex[i] := snakex[i-1]
snakey[i] := snakey[i-1]
gfx.Sprite(@dot_gfx, snakex[i], snakey[i], 0)
lcd.DrawIn essence, we now have a snake, not just a single dot, that can move around the field.
Growing up fast
Before we can see it in action, the tail has to get longer. Now, we could make the tail longer at startup, but that’s harder and requires extra code.
For now, let’s just add a little snippet to increase the tail length one by one, which is close to how it’ll work when the game is finished anyway. You can put it anywhere in the loop, but I choose to group it with all the other controls.
Snake.spin
repeat
gfx.Clear
ctrl.Update
if ctrl.A
if snakecount < constant(MAX_LENGTH-1)
snakecount++
if snakedir == LEFT or snakedir == RIGHTNow your snake is bigger and stronger than ever before!