Collision detection issues...

[Insectoid]

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:

Turing:

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

[btiffin]

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.

[Tony]

@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.

Turing:

exit when Math.Distance(targetx, targety, charx, chary) <= 10

[btiffin]

Tony @ Thu Apr 24, 2008 10:24 pm wrote:

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

Well Tony, I must say; hanging out here, I'm going to have to unfurl a Turing and take it for a spin. It seems to inspire. It sure doesn't hurt having smart people that seem to have this stuff down cold to bounce questions off either. So far I'm learning by osmosis.

Cheers

[Insectoid]

Thanks Tony. I did check the tutorial, but didn't find it helpful as it was...not very good, and painful to read (Dan has to work on his spelling). As I said, this is my first time going outside text and letters moving in a pre-determined route around the screen.

Being the kind of guy I am, I would now like to know what Math.Distance does. (I suppose it calculates the distance between the points you put in parantheses)

[gitoxa]

Math.Distance finds the distance between two points (x1, y1) and (x2, y2) using the distance formula

distance = square root of( (x2 - x1)^2 + (y2 - y1)^2 )