Image Collision

BlitzMax Forums/BlitzMax Beginners Area/Image Collision

TwoCorin517

(Posted 2008) [#1]

I'm sure this is pretty simple, when you have an image collision does it also include the alpha pixels?

Like if I have an image that's on top of the player, but the inside is (0,0,0) and that's the masked color, does ImagesCollide register it?

tonyg

(Posted 2008) [#2]

It doesn't use alpha or mask in the collision test. A quick test suggests it causes a bit of slowdown though if you have an image within a hole of another and you're checking collisions.

TwoCorin517

(Posted 2008) [#3]

so it records the collision then?

tonyg

(Posted 2008) [#4]

No. Sorry I can see how it is poorly worded. Alpha and mask pixels are not included in the collision test. I think the performance issue is because a rect collision is performed first (I think).
Anyway, it should be simple to test using :

Strict


Graphics 640,480

AutoMidHandle True	'image will rotate around it's center

Local image:TImage=LoadImage("circle.png")     '64*64 with 20 diameter circle
Local image2:timage=LoadImage("hollow_rect.png") ' 64*64 hollow rect
Local x:Int,y:Int
While Not KeyHit(KEY_ESCAPE)
	Cls
	ResetCollisions

' draw the first image at 5 times the size and on an arbitrary angle
	

	DrawImage image2,200,200

' add the first image to the first collision layer at same postion, rotation 
' and scale as it has just been drawn

	CollideImage image2,200,200,0,0,1

' move the other image relative to the mouse and rotate it continuously

	x=MouseX()
	y=MouseY()-20

	DrawImage image,x,y

' test the image at it's current rotation, scale and position with images
' that have been added to the first collision layer

	If CollideImage(image,x,y,0,1,0)

' reset scale and rotation states so our text is drawn correctly		
		DrawText "COLLISION!",20,20

	EndIf

	Flip
Wend