Computer Science Canada

moving and shooting
Author:  msimard8 [ Wed Jun 29, 2005 10:32 am ]
Post subject:  moving and shooting
Hello

How do you move a object and shoot something out of it ...and have the bullet moving while your moving aswell.

ya i know that question may be hard to understand. The code is part of what I have done, and you will see what i mean. I freeze until the bullet stops moving.

code:


setscreen ("graphics:649;479")
var gx, gy : int := 20
var key : array char of boolean
var ly : int := 20
var lx : int := 30
var weaponex : int := 370

proc background
    drawfillbox (0, 0, 500, maxy, black)
end background


proc scoreboard
    drawfillbox (501, 0, 649, 479, 12)
end scoreboard

%checks input keys
proc press

        if key (KEY_UP_ARROW)
                then
            gy := gy + 1
            ly := ly + 1
        end if

        if key (KEY_LEFT_ARROW)
                then
            gx := gx - 1
            lx := lx - 1
            weaponex := weaponex + 1
        end if

        if key (KEY_DOWN_ARROW)
                then
            gy := gy - 1
            ly := ly - 1
        end if

        if key (KEY_RIGHT_ARROW)
                then
            gx := gx + 1
            weaponex := weaponex - 1
            lx := lx + 1
        end if

        if gx < -80 then
            weaponex := 480
        elsif gx > 389 then
            weaponex := 0
        end if

end press


%.........fireing bullet animation
proc gun

    setscreen ("nooffscreenonly")
    for c : 1 .. weaponex
   
        scoreboard
        background
        drawfilloval (100 + gx, 100 + gy, 10, 10, red)
        drawfilloval (100 + lx + c, 100 + ly, 2, 2, yellow)
   
        setscreen ("offscreenonly")
 
        View.Update
 
    end for

end gun



%.......allows guy to move around and activates weapon
proc good

    loop
     
        background
        scoreboard
       
        delay (5)
        Input.KeyDown (key)
        drawfilloval (100 + gx, 100 + gy, 10, 10, red)

   setscreen ("offscreenonly")
press

        if key ('a') or key ('s') or key ('d') or key ('w')
                then
            gun
        end if
        View.Update
        cls
end loop

end good

good
Author:  Cervantes [ Wed Jun 29, 2005 11:26 am ]
Post subject: 
This will require you to learn some new concepts.
Turing Walkthrough -> Arrays -> Flexible Arrays
In the flexible array tutorial, there is an example of this very thing.
It would also be good to know how to use records to keep things organized and to same you some code when you have to remove a bullet.
Author:  msimard8 [ Thu Jun 30, 2005 2:43 pm ]
Post subject:  ?
I dont understand how to incorperate flexible arrays and records to solve this problem

thanks
Author:  Cervantes [ Fri Jul 01, 2005 7:08 am ]
Post subject: 
Have you read my tutorial and looked at the source code?

Make a flexible array of bullets:
code:

var bullet : flexible array 1 .. 0 of
   record
      x, y, vx, vy : real
   end record


When you hit the fire button (via Input.KeyDown), incriment the flexible array.
code:

new bullet, upper (bullet) + 1
bullet (upper (bullet)).x := player.x
bullet (upper (bullet)).y := player.y
%3 + player.velocity represents the velocity of the bullet
bullet (upper (bullet)).vx := cosd (player.angle) * (3 + player.velocity)  bullet (upper (bullet)).vy := sind (player.angle) * (3 + player.velocity) 

Notice how I added that 3 + player.velocity. Remember we're not shooting beams of light here. Wink

Movement of the bullet is like such:
code:

bullet.x += bullet.vx
bullet.y += bullet.vy


When you want to delete the bullet (it has collided with something or gone passed its range):
code:

bullet (bulletToDelete) := bullet (upper (bullet))
new bullet, upper (bullet) - 1

See here we are copying the upper bullet to the position of the one we want to delete and then deleting the original upper bullet. If you want to keep the bullets in "order", you'll need a for loop:
code:

for i : bulletToRemove + 1 .. upper (bullet)
    bullet (i - 1) := bullet (i)
end for
new bullet, upper (bullet) - 1


Hope that helps

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