Line interesecting oval

BlitzMax Forums/BlitzMax Beginners Area/Line interesecting oval

SillyPutty

(Posted 2005) [#1]

Hi all

How can i detect if a line I am drawing intersects an oval ?

MrCredo

(Posted 2005) [#2]

you must search for a line-circle-collision-routine

and only what you should do is to strech a line and a oval (oval->circle) with a factor....

for example:
your oval is 100x50 px (at 70,70 coordinate) and your line is from 0,0 to 100,100

your stretch factor is 2.0 (=100:50)

after stretching:
100,100 oval (at 70,140) and line 0,0-100,200

SillyPutty

(Posted 2005) [#3]

can a math guru please help me out with this one ? I got this routine off the net, but cant get it to work, an have no idea why.

Strict

Type vector2d
	Field x:Int
	Field y:Int

End Type

Const R:Int = 15

Global p1:vector2d = New vector2d
Global p2:vector2d = New vector2d
Global p3:vector2d = New vector2d
Global p:vector2d = New vector2d
Global m:Float

p1.x = 250;p1.y=250
p2.x = 400;p2.y=300

Graphics 800,600,32

Function pointincircle:Int(p:vector2d,c:vector2d)
	Return r*r >= getlength(c,p) 
End Function 

Function getlength:Int(v1:vector2d,v2:vector2d)
 Return	(v2.x-v1.x) * (v2.x-v1.x) + (v2.y-v1.y) * (v2.y-v1.y) 
End Function

While Not KeyDown(key_escape)

	p3.x = MouseX()
	p3.y = MouseY()
	
	DrawOval(p3.x,p3.y,R*2,R*2)
	DrawLine p1.x,p1.y,p2.x,p2.y

	
	
	
	m=(p2.y-p1.y)/(p2.x-p1.x)
	p.y = (m*(m*p3.y+p3.x-p2.x)+p2.y)/(1+m*m)
	p.x = p3.x + m*(p3.y-p.y)
	
	If(p.x >= p1.x And p.x <= p2.x) Or (p.x < p1.x And p.x > p2.x) Then 	DrawText "On Line Collision",100,100
	If(r*r >= getlength(p3,p)) Then DrawText "end point collision",100,100
	ElseIf (pointincircle(p1,p3)) Then DrawText "end point collision",100,100
	ElseIf (pointincircle(p2,p3)) Then DrawText "end point collision",100,100
		
	
	DrawOval p.x,p.y,5,5
	DrawLine p3.x,p3.y,p.x,p.y

	Flip
	Cls
Wend

SillyPutty

(Posted 2005) [#4]

this seems to work

Strict

Function intersection:Float(x1:Float,y1:Float,x2:Float,y2:Float,x3:Float,y3:Float,r:Float)


Rem 
	x1,y1,z1 p1 coords (point of line)
	x2,y2,z2 p2 coords (point of line)
	x3,y3,z3 p3 coords and radius (sphere)
	x,y,z intersection

End Rem

Local x:Float
Local y:Float
Local a:Float
Local b:Float
Local c:Float
Local mu:Float
Local i:Float
Local p:Float[7]

a = (x2-x1)^2 + (y2-y1)^2 
b = 2*((x2-x1)*(x1-x3)+(y2-y1)*(y1-y3))
c = x3^2 + y3^2 + x1^2 + y1^2 - 2*(x3*x1+y3*y1) - r^2

i = b*b - 4*a*c

If ( i < 0) Then
 p[0] = 0
 Return 0
End If

If(i=0) Then
 p[0] = 1
 Return 1 
End If

If(i > 2) Then
 Return 2
End If


Return 0
End Function


Graphics 800,600,32

While Not KeyDown(key_escape)

	DrawLine 10,10,100,100
	
	DrawOval MouseX(),MouseY(),30,30

	Local g:Float=0
	
	Local dx:Float = MouseX() - 10
	Local dy:Float = MouseY() - 10
	
	Local mag:Float = Sqr(dx^2 + dy^2)
	
	Local dlx:Float = 100-10
	Local dly:Float = 100-10
	
	Local linemag:Float = Sqr(dlx^2+dly^2)
	
	If mag <= linemag Then
		g = intersection(10,10,100,100,MouseX(),MouseY(),15)

		If g > 0 Then DrawText "Collision!",100,100
	End If
	
	
	
	DrawText mag, 200,200
	
	Flip
	Cls
Wend