OVal detection

[upthescale]

I am makign a fish game, where i have to eat bigger fish, and if bigger fish eat u you lose. But the other fish are on a random size, they will always be an oval, there y size is the random part. Whats the best way to do a hit detection with ovals?

[MysticVegeta]

how about Math.Distance??

[upthescale]

I am trying, but that is usually for circles, not ovals

[the_short1]

..yes you can.. math.distance can be used... but not directly..
http://en.wikipedia.org/wiki/Ellipse
you the properties of the ellipse... and some advanced math concepts.. if you havnt learned about ellipses in math.. i would recomend making them circles instead.. i can do it .,., but tahts calculus and discreet under my belt . . and i dont have time to write it for you.. srry

[Mazer]

You could try to work your way through this.

If that's too complicated and/or the ovals in question are long enough you might want to try treating them as rectangles for a rough approximation of collision detection (or better yet, a series of smaller rectangles that make up a rough oval shape).

[MysticVegeta]

Here is a demo I made to detect for oval collision:

Advantages are: Well that you have oval detection now.
Disadvantages are: Its too slow, Its only valid for integral x,y values of collision. ie: If the ovals only collide when x not= n and y not= n, where n is an integer, then it wont work.

code:

var x1 := Rand.Int (1, maxx) var x2 := Rand.Int (1, maxx) var y1 := Rand.Int (1, maxy) var y2 := Rand.Int (1, maxy) var c := Rand.Int (20, 200) var c1 := Rand.Int (20, 200) var c2 := Rand.Int (20, 200) var c3 := Rand.Int (20, 200) drawfilloval (x1, y1, c, c1, brightred) drawfilloval (x2, y2, c2, c3, brightblue) fcn collide (x1 : int, y1 : int, x2 : int, y2 : int, c : int, c1 : int, c2 : int, c3 : int, p : int, q : int) : boolean     /* GENERAL EQUATION OF AN ELLIPSE IS:      (X - H) ^ 2   +   (Y - K) ^ 2      -----------      -------------  = 1      A^2               B^2      A is Radius # 1.      B is Radius # 2.      (H, K) is the centre. Here, it cant be negative, but it could if graphed on Cartesian plane.      (X, Y) are non-constant variables.      Strategy: Loop through all (x, y) plug in to see whether any of the coordinates satisfy equation for both ellipses      */     for x : 1 .. p         for y : 1 .. q             var eq1 := (((x - x1) ** 2) / (c ** 2)) + (((y - y1) ** 2) / (c1 ** 2))             var eq2 := (((x - x2) ** 2) / (c2 ** 2)) + (((y - y2) ** 2) / (c3 ** 2))             if (round (eq1) = 1 and round (eq1) = round (eq2)) then                 result true             end if         end for     end for     result false end collide if (collide (x1, y1, x2, y2, c, c1, c2, c3, maxx, maxy)) then     put "These ovals collide" else     put "These ovals do not collide" end if

[BenLi]

surprised that nobody said it yet... but you could always dumb it down to whatdotcolor...

[MysticVegeta]

And how do you suppose you would do that with whatdotcolor? There is no way you can do that with whatdotcolor unless ofcourse you are Andy. but it will be complicated since you cant really loop thourgh all the pixels of any of the ovals.

[MysticVegeta]

Hmm I am sort of wondering if we can use some geometry to do this, for eg: using major and minor radii. I have got this so far but it doesnt give correct answer all the time, there are 2 methods I used:

code:

var x1 := Rand.Int (1, maxx) var x2 := Rand.Int (1, maxx) var y1 := Rand.Int (1, maxy) var y2 := Rand.Int (1, maxy) var c := Rand.Int (20, 200) var c1 := Rand.Int (20, 200) var c2 := Rand.Int (20, 200) var c3 := Rand.Int (20, 200) drawfilloval (x1, y1, c, c1, brightred) drawfilloval (x2, y2, c2, c3, brightblue) fcn collide2 (x1 : int, y1 : int, x2 : int, y2 : int, c : int, c1 : int, c2 : int, c3 : int) : boolean     %  if (Math.Distance (x1, y1, x2, y2) <= (min (c, c1) + min (c2, c3))) and     % (Math.Distance (x1, y1, x2, y2) <= (max (c, c1) + max (c2, c3))) then     if (Math.Distance (x1, y2, x2, y2) <= (max (c, c1) + max (c2, c3)) div 2) then         result true     end if     result false end collide2 if (collide2 (x1, y1, x2, y2, c, c1, c2, c3)) then     put "These ovals collide ", x1, " ", y1, " ", x2, " ", y2 else     put "These ovals do not collide ", x1, " ", y1, " ", x2, " ", y2 end if

[MysticVegeta]

wait ignore the post above, I have been thinking and came up with 3 scenarios.

If the Distance between the centres is less than the sum of the minor radii of both the oval, then 100% they are colliding.

If the Distance between the centres is greater than the sum of the major radii of both the oval, then 100% they are NOT colliding.

If the Distance between the centres is > sum of minor radii but < sum of major radii, then more scenarios in this on arise, I dont know how to find a solution to this scenario...

Does someone has a lead in this scenario?

[TheOneTrueGod]

Well, since like 8 other people gave you code, I might as well also.

code:

function Dist (x1, y1, x2, y2 : real) : real     result sqrt ((x2 - x1) ** 2 + (y2 - y1) ** 2) end Dist var mx, my, but : int var ovx, ovy, ovXSize, ovYSize := 100 ovYSize := 20 loop     drawfilloval (ovx, ovy, ovXSize, ovYSize, black)     mousewhere (mx, my, but)     locate (1, 1)     if sqrt (((ovx - mx)) ** 2 + ((ovy - my) * (ovXSize / ovYSize)) ** 2) < 100 then         put "It Hit"     else         put ""     end if end loop

[Clayton]

Good job as always TOTG, however i have one question to ask: why did you include fcn Dist if you didnt use it??? anyways, in case anyone hasnt noticed, upthescale has been banned, so why are we posting in this topic?

[Slaivis]

SuperFreak82 wrote:

Good job as always TOTG, however i have one question to ask: why did you include fcn Dist if you didnt use it??? anyways, in case anyone hasnt noticed, upthescale has been banned, so why are we posting in this topic?

Just because the op can no longer use the information, that doesn't mean that the rest of us can't.

I sure plan to use TOTG's code if I find a use for it!

[MysticVegeta]

TheOneTrueGod wrote:

Well, since like 8 other people gave you code, I might as well also.

code:

function Dist (x1, y1, x2, y2 : real) : real     result sqrt ((x2 - x1) ** 2 + (y2 - y1) ** 2) end Dist var mx, my, but : int var ovx, ovy, ovXSize, ovYSize := 100 ovYSize := 20 loop     drawfilloval (ovx, ovy, ovXSize, ovYSize, black)     mousewhere (mx, my, but)     locate (1, 1)     if sqrt (((ovx - mx)) ** 2 + ((ovy - my) * (ovXSize / ovYSize)) ** 2) < 100 then         put "It Hit"     else         put ""     end if end loop

I sort of knew that too. But What I was asking was to detect collision betwen 2 ovals.. btw: What formula did you use?

[TheOneTrueGod]

Er, ya, I was going to use the Dist formula orginally, but then I used a modified one, and forgot to take it out .

And I just experimented with the properties of a circle and an oval. Used some random formulas that made sense to me, etc.

As for collision between two ovals, I'd have to work on it a bit more, but something along the lines of

-Find the closest point from oval 1 to oval 2. (Use trig / oval properties for this.)
-Use the oval formula from before.

I may or may not make up some'n, if I feel like it, and post it later.

As for why this topic is still alive, i'd say its something to have if someone who has the same question later on feels like searching...
I know that only happens like... once a week... but still. Thats one less question a week that doesn't need to be answered .