Few mathsey problems

phaxx

I'm writing a little game at the moment, and have become kind of stuck. I'd be grateful for any help anyone can provide.

It's a little windows Spacewar! clone, and I need some kind of collision-detection, because it's pretty damn useless otherwise!

First problem is to know when a missile has hit a spaceship, or to put it another way, when a given point is within a given circle.

The information I'd have for this is:
mX,mY, missile x and y co-ords

sX, sY, spaceship center co-ords, and sR, radius of the circle.

I really have no idea how to go about this...

The other problem is the lasers, I need to know if a line goes through a given circle. Could probably adapt the solution of the above problem?

Information available for this is the x,y values of both points of the line (laser) and the circle x,y and radius as above.

Please help, game is useless without collision detection

nesf

It's not complicated really, you could just write a subroutine to check if either if
the distance (mx,my) to (sx,sy) is = sR

If it is then a missile has hit. You can use simple junior cert level geometry for this.

You could write a more complicated sub for the second prob, where you check the perp distance from the line to the centre of the spaceship circle, leaving cert formula, if this is <= sR then you got a hit.

Any help to you?

The Pinky

Yeah nesf is right there

Just create a subroutine that checks to see if the missle x,y is less than the radius distance of the ship x,y

e,g

Ship x,y = 5,2 We'll call then x1, and y1
Missle x,y = 7, 3 Call these x2,y2
Radius = 4

Distance between two points formula

square root of:
(x1-x2)squared + (y1-y2)squared
(5-7)squared + (2-3)squared
(-2)squared + (-1)squared
4 + 1
= 5
square root of 5 = 2.23
5 is less than the radius
therefore a hit!!

At least I think I'm right someone better back me up on this!!

Richey

---

Narf!!!

[This message has been edited by The Pinky (edited 02-08-2001).]

phaxx

I have a distance formula already that works grand.

d = sqr( (x1 * y2) - (x2 * y2) )

The only problem now is the line one, but I think I can solve that by getting a few points along the line, 25%, 50%, 75% and 100%, and because the length of the line(laser) and size of the ship is constant, I can make sure one of those points is inside the ship's hitbox (circle, whatever)

Does anyone have a better way?

Bob the Unlucky Octopus

Moved to programming- the math folks there could probably help you more

Bob the Unlucky Octopus

nesf

Aye, I do, it's stated above

Get a leaving cert maths, hons, book and check the line geometry section for the formula for finding the perp distance between a line and a point. If this distance is less than or equal to the lenght of the radius then you got yourself a hit.

It's simple and only requires one formula.

seamus

or..If you really wanna try some funky-ass progamming, try the intesection of line and circle circumference formula, found once again in any leaving cert hons maths book. Basically if any value is found, it's a hit, and if an error msg is returned (infinite or illogical value) it's not a hit

AzReAl

Here i am seeking to get into computer programming and math problems arise....NOOOOOO

phobos

As the lads b4 have said. All you have to do is implement Pythagoras's Theorem, it's very easy.

So to calc the radius between ships or their scope whatever use this formula

radius_scope = sqrt(opposite² + adjacent²)

All you have to do then is each time movement occurs, check to see if an object is <= a centain radius_scope to check for a collision.

;-phobos-)