1945 simplified

[Marcus]

Regarding collision, "just" check if two images overlap. It's easier to understand if you draw some on a paper
...

Your collision detection code is wonderful, it works like magic. 
Now when a bullet hits an enemy, the enemy disappeares 

Thanks also for your advice to avoid flickering graphics by 'set redraw off' and 'redraw' 

Code:

'------ revised code to reflect some improvements -------

'INITIALIZATION
set window "1945 Simplified", 640, 480
set redraw off 'faster, removes flickering graphics
load image 1,"data_1945/plane.png"
load image 2,"data_1945/bullet.png"
load image 3,"data_1945/enemy.png"
load image 4,"data_1945/black.png"

speed=4
planeX=640/2        ; planeY=400
bulletX = planeX+15 ; bulletY = planeY
enemyX = []         ; enemyY = []
enemyX[0] = 40      ; enemyY[0] = -10
enemyX[1] = 300     ; enemyY[1] = -50
enemyX[2] = 400     ; enemyY[2] = -30

'MAIN PROGRAM
do
    'SET BACKGROUND
     cls
     draw image 4,0,0

     'THE PLANE
     draw image 1,planeX,planeY
                       
    'ESC TO QUIT, LEFT AND RIGHT KEYS TO MOVE THE PLANE
     if keydown(KEY_ESCAPE) then end
     if keydown(KEY_LEFT)   then planeX=planeX-speed
     if keydown(KEY_RIGHT)  then planeX=planeX+speed

     'ENEMIES
     for x=0 to 2
        'collision detection if bullet and enemy image overlap
        dead = bulletX + width(2) > enemyX[x] and bulletX < enemyX[x] + width(3) and
            bulletY + height(2) > enemyY[x] and bulletY < enemyY[x] + height(3)
        if enemyY[x]>480 or dead then
            enemyX[x]=rnd(640)
            enemyY[x]=-rnd(50)
         else
            enemyY[x]=enemyY[x]+speed
         endif
      next

      for x=0 to 2
        draw image 3,enemyX[x],enemyY[x]
      next
           
     'BULLET, AUTO SHOOT   
      if bulletY < 480 then
        bulletY   =   bulletY - speed*3
      endif
     
      if bulletY = 100 then
        bulletX = planeX+15
        bulletY = planeY
      endif         
                                
      draw image 2,bulletX,bulletY

     'WAIT BEFORE LOOPING
      redraw 'faster, removes flickering graphics
      wait 40
loop

No problems! I've added two more versions of your program, but you can ignore them for now if they seem confusing

In 1945_2.n7 I've replaced your two arrays, enemyX and enemyY, with a 2D array, so that the x value of enemy n is in enemy[n][0] and the y value is in enemy[n][1].

1945_3.n7 is a modification of 1945_2.n7, but instead of using enemy[n][0] and enemy[n][1] for position, I use enemy[n].x and enemy[n].y, which makes it easier to read the code.


The . (dot) notation, as in enemy[n].x, really isn't a complicated thing. In n7 you can use both numbers and strings as "keys" to tables. An array is what I call a table where only numeric keys (indexes) are used.

This is an array:

Code:

hello = []
hello[0] = 13
hello[1] = 12
pln "1: " + hello[1]

But you can also do this:

Code:

hello = []
hello["what"] = 13
hello["weird"] = 14
pln "weird: " + hello["weird"]

And the above is the exact same thing as:

Code:

hello = []
hello.what = 13
hello.weird = 14
pln "weird: " + hello.weird

I hope I'm not confusing you or anone else.