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Insectoid

Thu Apr 24, 2008 8:49 pm


Collision detection issues...

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I just learned today how to do character movement from a tutorial on this site somewhere and well, movement isn't usefull without collision detection. 

However, My mini-project for fun seems to do something...wrong. The little red circle (controlled by arrow keys) is supposed to hit a black dot, which is then randomly placed somewhere else on the screen. What happens instead is that once the red dot crosses the x- axis of the black dot and subsequently crosses the y- axis, THEN it moves the black dot. 

Here's my code: 


var charx : int := 100
var chary : int := 100
var targetx : int
var targety : int
var num : array char of boolean
loop
    targetx := Rand.Int (10, 630)
    targety := Rand.Int (10, 390)
    loop
        exit when charx + 6 >= targetx + 6 and chary + 6 >= targety + 6
        Draw.FillOval (targetx, targety, 5, 5, black)
        Draw.Oval (charx, chary, 5, 5, brightred)
        Input.KeyDown (num)
        if num (KEY_UP_ARROW) and chary < 390 then
            chary := chary + 5
        end if
        if num (KEY_DOWN_ARROW) and chary > 10 then
            chary := chary - 5
        end if
        if num (KEY_LEFT_ARROW) and charx > 10 then
            charx := charx - 5
        end if
        if num (KEY_RIGHT_ARROW) and charx < 630 then
            charx := charx + 5
        end if
        delay (10)
        cls
View.Update
    end loop
end loop



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btiffin

Thu Apr 24, 2008 9:59 pm


Re: Collision detection issues...

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Hi,

   I don't know Turing and should probably leave this to some of the other compsci members, but;

Your charx targetx test is ANDed with the chary targety test.  Would OR be more appropriate?

Cheers from the clueless old guy.


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Tony

Thu Apr 24, 2008 10:24 pm


RE:Collision detection issues...

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@btiffin -- I'm sure that you could still read that code ;)

@insectoid -- read your condition statement. You are checking if char is to the right and above the target. There's quite a lot of area in that box.

also: charx + 6 >= targetx + 6 is the same as
charx >= targetx. Less magic numbers makes more sense.

If you were to follow the tutorials to read up on the collision detection, you'd learn that collision occurs when two objects overlap. That is, the right-most point of A is to the right of the left-most point of B and the left-most point of A is to the left of the right-most point of B and similar set of conditions for the Y-axis.

That's a lot to check. It's also a square shape. A shortcut for two circles is that collision occurs when the distance between the centers is less than the sum of the radiuses.


exit when Math.Distance(targetx, targety, charx, chary)