Framework/code for entities?

[Robin]

There's a tutorial game that does what I want to do, destruction.love: I need to remove a entity from the game. Now I just need to find out how this works. =D

Oh, you meant destroying Bodies! You can call somebody:destroy(), and remove all references to it. Hope this helps.

[dbltnk]

You were right, collision detection via Box2D is really tedious and not really what I'm looking for.

Is there an equivalent for the Actionscript 3.0 function hitTestObject() in LÖVE/LUA? The only thing I need to know is if two images collide. A simple true/false is all I'm looking for. =D

[Robin]

You were right, collision detection via Box2D is really tedious and not really what I'm looking for.

Is there an equivalent for the Actionscript 3.0 function hitTestObject() in LÖVE/LUA? The only thing I need to know is if two images collide. A simple true/false is all I'm looking for. =D

It depends. If you want to compare two rectangles, it's pretty simple:

Code: Select all

function collide(obj1, obj2) --obj1 and obj2 are assumed to be tables with these fields: x, y, w, h
    if (obj1.x > obj2.x and obj1.x < obj2.x + obj2.w) or (obj2.x > obj1.x and obj2.x < obj1.x + obj1.w) then
        if (obj1.y > obj2.y and obj1.y < obj2.y + obj2.h) or (obj2.y > obj1.y and obj2.y < obj1.y + obj1.h) then
            return true
        end
    end
end

(or something like that, I'm not sure... it's somewhere on the wiki and forums already, but I'm too lazy to find it )

For two circles, it's even easier:

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function collideCircle(obj1, obj2) --tables with fields x, y, r
    return math.sqrt((obj1.x-obj2.x)^2 + (obj1.y-obj2.y)^2) < obj1.r + obj2.r
end

[bartbes]

In your first collision function you forget to return false if it is not the case, even though it returns nil now, I think it's better coding style to at least return something. (and note that nil ~= false)

[Robin]

In your first collision function you forget to return false if it is not the case, even though it returns nil now, I think it's better coding style to at least return something. (and note that nil ~= false)

Again: laziness.

[dbltnk]

Thanks for the input guys. I've written that circle collision detection yesterday and wanted to to implement boxes today. Then it's time for combining those and I'm all set-up. Maybe I'll post the code here so that not everyone has to re-invent the wheel for something supposedly simple as collision detection.

[dbltnk]

Functions for collisions between two rectangles or two circles are done. Now I'm trying to find a way to combine those into a function that does good collision detection between a circle and a box. This is pretty hard as my math skills are way to rusty. *g*

Anyways, here are my current collision functions:

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function collide_circle(x1,y1,r1,x2,y2,r2)
	local dx = x1-x2
	local dy = y1-y2
	if dx^2+dy^2 < (r1+r2)^2 then return true else return false end
end

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function collide_box(x3,y3,w3,h3,x4,y4,w4,h4)    
	if ((x4 > (x3 + w3/2 + w4/2 )) or (x3 > (x4 + w4/2 + w3/2 )) or (y4 > (y3 + h3/2 + h4/2)) or (y3 > (y4 + h4/2 + h3/2)) ) then return false else	return true end
end

And the not-yet-working one with false positives for rectangle and circle:

Code: Select all

function collide_circle_box(x1,y1,r1,x3,y4,w3,h3)
	if ((x1 > (x3 + w3/2 + r1 )) or (x3 > (x1 + r1 + w3/2 )) or (y1 > (y3 + h3/2 + r1)) or (y3 > (y1 + r1 + h3/2)) ) then return false else return true end
end

[Robin]

I'm not sure, but I think you have to include a circle vs point collision function, because a rectangle has four points (corners). If you've checked that, I think you only need to check whether the midpoint of the circle is inside the rectangle (ie x1 < x_circle < x2 and y1 < y_circle < y2).

[dbltnk]

I'm done with the first version of my collision "framework". So far it's not very useful as it only checks for collisions between hard-coded objects. My next step will be the creation of a object table with whom I'll be able to spawn circle and rectangle objects. The collision framework will then use the appropriate function to check for collision, depending on the objects being two circles, two rectangles or a circle and a rectangle.

What do you think of the collision code so far? Where can it be improved?

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function load()
	-- Load images.
	images = {
        circle1 = love.graphics.newImage("/Assets/circle1.png"),
	circle2 = love.graphics.newImage("/Assets/circle2.png"),
	box3 = love.graphics.newImage("/Assets/box3.png"),
	box4 = love.graphics.newImage("/Assets/box4.png"),
	}
    	--set up the font and some texts that will be used later
    	font = love.graphics.newFont(love.default_font, 10) 
	love.graphics.setFont(font) 
	debug_circle = "empty"
	debug_box = "empty"
	debug_circle_box = "empty"
	helptext = "Press 1-4 to randomly move the objects. R = Reset. ESC = Exit."
	--set up the variables for the two circles
	x1 = 120
	y1 = 150
	r1 = 78
	x2 = 300
	y2 = 150
	r2 = 57
	--set up the variables for the two rectangles
	x3 = 120
	y3 = 295
	w3 = 100
	h3 = 100
	x4 = 290
	y4 = 295
	w4 = 140
	h4 = 70
end

function update(dt)
	--every few milli-seconds, this runs the functions that check for collisions
	collide_circle(x1,y1,r1,x2,y2,r2)
	collide_box(x3,y3,w3,h3,x4,y4,w4,h4)
	collide_circle_box(x1,y1,r1,x3,y4,w3,h3)
	--x1 = love.mouse.getX() --uncomment this is you want to stick the blue rectangle to your mouse
	--y1 = love.mouse.getY() --uncomment this is you want to stick the blue rectangle to your mouse
end

function draw()
	-- here the four sprites are drawn
	love.graphics.draw(images.circle1,x1,y1)	
	love.graphics.draw(images.circle2,x2,y2)
	love.graphics.draw(images.box3,x3,y3)
	love.graphics.draw(images.box4,x4,y4)
	--text output telling you which collisions happened
	if collide_circle(x1,y1,r1,x2,y2,r2) == true 
	then debug_circle = "The circles collide." 
	else debug_circle = "The circles don't collide." 
	end
	if collide_box(x3,y3,w3,h3,x4,y4,w4,h4) == true 
	then debug_box = "The boxes collide." 
	else debug_box = "The boxes don't collide." 
	end
	if collide_circle_box(x1,y1,r1,x3,y4,w3,h3) == true 
	then debug_circle_box = "Circle1 and box3 collide." 
	else debug_circle_box = "Circle1 and box3 don't collide." 
	end 
	love.graphics.draw(debug_circle,10,20)	
	love.graphics.draw(debug_box,10,35)
	love.graphics.draw(debug_circle_box,10,50)
	love.graphics.draw(helptext, 10, 390)
end

function collide_circle(x1,y1,r1,x2,y2,r2)
	-- this function checks for a collision between the two circles
	local dx = x1-x2
	local dy = y1-y2
	if dx^2+dy^2 < (r1+r2)^2 
	then return true 
	else return false 
	end
end

function collide_box(x3,y3,w3,h3,x4,y4,w4,h4)    
	-- this function checks for a collision between the two rectangles
	if ((x4 > (x3 + w3/2 + w4/2 )) 
	or (x3 > (x4 + w4/2 + w3/2 )) 
	or (y4 > (y3 + h3/2 + h4/2)) 
	or (y3 > (y4 + h4/2 + h3/2)) ) 
	then return false 
	else return true 
	end
end

function collide_circle_box(x1,y1,r1,x3,y4,w3,h3)
	-- this function checks for a collision between the first circle and the cirst rectangle
	local dx = math.abs(x1 - x3);
	local dy = math.abs(y1 - y3);
	if dx > (w3/2 + r1)
	then return false
	end
	if dy > (h3/2 + r1)
	then return false
	end
	if (dx <= (w3/2)) 
	then return true
	end
	if (dy <= (h3/2)) 
	then return true
	end
	local dc = (dx - w3/2)^2 + (dy - h3/2)^2
	if dc <= r1^2
	then return true
	else
	return false
	end
end

function keypressed(key)
	--exit the game when ESC is pressed
	if key == love.key_escape then love.system.exit() end
	--restart the game when R is presses
	if key == love.key_r then love.system.restart()	end
	--move each sprite to a random location when the appropriate key (1-4) is pressed
	if key == love.key_1 then x1 = math.random(50,350) y1 = math.random(50,350) end
	if key == love.key_2 then x2 = math.random(50,350) y2 = math.random(50,350) end
	if key == love.key_3 then x3 = math.random(50,350) y3 = math.random(50,350) end
	if key == love.key_4 then x4 = math.random(50,350) y4 = math.random(50,350) end
	--move the first rectangle when an arrow key is pressed
	if key == love.key_down then y3 = y3+20 end
	if key == love.key_up then y3 = y3-20 end
	if key == love.key_left then x3 = x3-20 end
	if key == love.key_right then x3 = x3+20 end
end