Point versus Polygon Collision

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SoCoder -> Snippet Home -> Collisions and Physics

Pakz	Created : 02 November 2019 Language : Monkey2 Point versus Polygon Collision Check if a point is inside a polygon
#Import "<std>" #Import "<mojo>" Using std.. Using mojo.. Class MyWindow Extends Window ' The variable for a line on the screen Field polygonx:Int[],polygony:Int[] Method New() polygonx = New Int[4] polygony = New Int[4] polygonx[0] = 50 polygony[0] = 50 polygonx[1] = 150 polygony[1] = 100 polygonx[2] = 150 polygony[2] = 200 polygonx[3] = 100 polygony[3] = 100 End Method Method OnRender( canvas:Canvas ) Override App.RequestRender() ' Activate this method ' ' drawpoly(canvas) If pointpolycollide(Mouse.X,Mouse.Y) =True Then canvas.Color = Color.White canvas.DrawText("Collision",0,0) End If canvas.Color = Color.White canvas.DrawText("Move mouse inside and outside of polygon",320,0) ' if key escape then quit If Keyboard.KeyReleased(Key.Escape) Then App.Terminate() End Method Method drawpoly(canvas:Canvas) canvas.Color = Color.White For Local i:Int=1 Until polygonx.GetSize(0) canvas.DrawLine(polygonx[i-1],polygony[i-1],polygonx[i],polygony[i]) Next canvas.DrawLine(polygonx[0],polygony[0],polygonx[polygonx.GetSize(0)-1],polygony[polygony.GetSize(0)-1]) End Method Method pointpolycollide:Bool(pointx:Int,pointy:Int) Local collisioncount:Int=0 Local sx:Int=Rnd(640),sy:Int=Rnd(480) If Rnd()<.5 Then sx-=1000 Else sx+=1000 If Rnd()<.5 Then sy-=1000 Else sy+=1000 For Local i:Int=1 Until polygonx.GetSize(0) If get_line_intersection(polygonx[i-1],polygony[i-1],polygonx[i],polygony[i],pointx,pointy,sx,sy) Then collisioncount+=1 Next If get_line_intersection(polygonx[0],polygony[0],polygonx[polygonx.GetSize(0)-1],polygony[polygony.GetSize(0)-1],pointx,pointy,sx,sy) Then collisioncount+=1 ' If (collisioncount Mod 2) > 0 Then Return True ' Return False End Method End Class Function Main() New AppInstance New MyWindow App.Run() End Function '// Returns 1 if the lines intersect, otherwise 0. Andre la moth. Function get_line_intersection:Bool(p0_x:Float, p0_y:Float, p1_x:Float, p1_y:Float, p2_x:Float,p2_y:Float, p3_x:Float, p3_y:Float) Local s1_x:Float, s1_y:Float, s2_x:Float, s2_y:Float s1_x = p1_x - p0_x s1_y = p1_y - p0_y s2_x = p3_x - p2_x s2_y = p3_y - p2_y Local s:Float, t:Float s = (-s1_y * (p0_x - p2_x) + s1_x * (p0_y - p2_y)) / (-s2_x * s1_y + s1_x * s2_y) t = ( s2_x * (p0_y - p2_y) - s2_y * (p0_x - p2_x)) / (-s2_x * s1_y + s1_x * s2_y) If (s >= 0 And s <= 1 And t >= 0 And t <= 1) Then Return True Return False '// No collision End Function End Function --v
Latest Update I am still looking to learn how to do polygon vs polygon collision. Today I figured out how to find collision with a polygon versus a point The method here is done with line collisions. You take a random point somewhere away of the polygon and then check collision with the to be checked point versus the lines of the polygon. If the point is inside the polygon then there wil be a uneven amount of collisions. If it is outside then a even amount of collisions. The original description said to use rays to check it, but I used lines since this seemed this would do the trick also.

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Saturday, 02 November 2019, 22:24
Pakz	I just noticed there was already a snippet for this here. Though there was no description and it was in another language.

Point versus Polygon Collision

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