OpenEuphoria

1. Collision Detection

• Posted by Andy Aug 08, 2009
• 1095 views
• Last edited Aug 09, 2009

Hey Guys,

I was playing around with Euphoria, and I was wondering how I would add some collision detection to this program? Its pretty simple, I just wanna add some collision detection, so I know when the images intersect with each other. Here's the code.

without warning 
without type_check 
 
include win32lib.ew 
include file.e 
include get.e 
include misc.e 
include wildcard.e 
 
if platform() != WIN32 then 
	puts(1,"Must run under Windows!\n") 
	abort(1) 
end if 
 
atom SizeX, 
SizeY 
 
SizeX = 640 
SizeY = 480 
 
constant Win = createEx(Window,"Simple Game",0,Default,Default,SizeX,SizeY,0,0), 
Stat = createEx(StatusBar,"",Win,0,0,0,0,0,0) 
 
atom Guy, 
Guy2 
Guy = loadBitmapFromFile("Stick.bmp") 
Guy2 = loadBitmapFromFile("Stick2.bmp") 
 
atom X, 
Y, 
X2, 
Y2 
 
X = 180 
Y = 35 
 
X2 = 280 
Y2 = 35 
 
procedure GameLoop(integer self, integer event, sequence parm) 
	integer key 
	key = parm[1] 
	 
	drawBitmap(Win,Guy,X,Y) 
	drawBitmap(Win,Guy2,X2,Y2) 
	 
	if key = VK_ESCAPE then 
		closeWindow(Win) 
	end if 
	 
	wPrintf({Win,1,1},"X:%d",{X}) 
	wPrintf({Win,1,12},"Y:%d",{Y}) 
	wPrintf({Win,1,25},"X2:%d",{X2}) 
	wPrintf({Win,1,42},"Y2:%d",{Y2}) 
	 
	if key = VK_LEFT then 
		X = X - 5 
		X2 = X2 + 5 
		drawBitmap(Win,Guy,X,Y) 
		repaintWindow(Win) 
	elsif key = VK_RIGHT then 
		X = X + 5 
		X2 = X2 - 5 
		drawBitmap(Win,Guy,X,Y) 
		repaintWindow(Win) 
	elsif key = VK_UP then 
		Y = Y - 5 
		Y2 = Y2 + 5 
		drawBitmap(Win,Guy,X,Y) 
		repaintWindow(Win) 
	elsif key = VK_DOWN then 
		Y = Y + 5 
		Y2 = Y2 - 5 
		drawBitmap(Win,Guy,X,Y) 
		repaintWindow(Win) 
	elsif X and Y = X2 and Y2 then 
		setText(Stat,"Images Hit") 
	end if 
	 
end procedure 
setHandler(Win,w32HPaint,routine_id("GameLoop")) 
setHandler(Win,w32HKeyDown,routine_id("GameLoop")) 
 
WinMain(Win,Normal) 

I plan on adding some other features to it later on, but I wanna get the collision detection down first.

3. Re: Collision Detection

• Posted by prickle Aug 09, 2009
• 1069 views

A simple method might be bounding boxes. Depending on the number of guys you have on the screen, it may be acceptably fast.

If we have the following functions:

--sign of r 
function sgn(atom r)                  
  if r < 0 then return -1 else return 1 end if 
end function 
--absolute value of r 
global function abs(atom r)                  
  return sgn(r) * r                              
end function 

(BTW, have these been included in more recent versions of Euphoria? If not, may I suggest them?)

We also need the size of your guys:

atom sx, sy, sx2, sy2 
sx = length(Guy[1][1]) 
sy = length(Guy[1]) 
sx2 = length(Guy2[1][1]) 
sy2 = length(Guy2[1]) 

(it still works this way, right?)

We then precalculate the difference between the midpoints of the guys when they are just touching.

atom dx, dy 
dx = floor((sx + sx2) / 2) 
dy = floor((sy + sy2) / 2) 

Then, where you have:

        elsif X and Y = X2 and Y2 then  
		setText(Stat,"Images Hit")  
	end if  

We can say:

        elsif abs(X - X2) < dx and abs(Y - Y2) < dy then  
		setText(Stat,"Images Hit")  
	end if  

Is it obvious what we are doing here? We are finding the difference between the positions of the guys and seeing if it is small enough for them to be touching. Of course this gives one a rectangular bounding box around a guy which may not be ideal for irregular shapes, but it is probably the cheapest, simplest method of collision detection I know.

Hope this helps.

Cheers,

Nick

5. Re: Collision Detection

• Posted by Andy Aug 09, 2009
• 1124 views

Yes, I am slowly getting it. CD isn't super easy for me to understand, but I am getting the grasp of it.