Knife Hit mechanics - how to?

Apollo14 · May 2018

Hi guys!
How would you create 'Knife Hit' prototype?
(original gameplay is here:

(I've attached my current gproj with PNGs)
How to pin thrown knives to circle and make them rotate with circle?

I'm thinking about creating invisible parent for thrown knives, remove them from original parent and add them to invisible parent, just I'm not sure how to do it properly. And maybe there's another better way?

Currently I'm stuck here:

application:setBackgroundColor(0x2f3640)
centerX@240
centerY@427
local function playSound(sound) Sound.new(sound):play() end
 
--Add knives:
local knivesArr={}
for i=1,7 do
	knivesArr[i] = Bitmap.new(Texture.new("pics/knife.png",true))
	knivesArr[i]:setScale(0.3)
	knivesArr[i]:setAnchorPoint(0.5,0.5)
	knivesArr[i]:setPosition(centerX, centerY+250)
	stage:addChild(knivesArr[i])
	knivesArr[i]:setVisible(false)
end
currentKnifeCount=1
knivesArr[currentKnifeCount]:setVisible(true)
 
--Add circle:
local circle = Bitmap.new(Texture.new("pics/circle.png",true))
circle:setScale(0.5)
circle:setAnchorPoint(0.5,0.5)
circle:setPosition(240, 220)
stage:addChild(circle)
 
--Add apple to circle:
local apple = Bitmap.new(Texture.new("pics/apple.png",true))
apple:setScale(0.7)
apple:setAnchorPoint(0.5,0.5)
apple:setY(-325)
circle:addChild(apple)
 
--Rotate circle every frame:
local function onEnterFrameFunc()
	circle:setRotation(circle:getRotation()+1)
end
stage:addEventListener(Event.ENTER_FRAME, onEnterFrameFunc)
 
--Throw knife on tap:
local function throwKnife()
	playSound("sounds/throw.mp3")
	local knifeTween=GTween.new(knivesArr[currentKnifeCount], .15, {y = 410}, {delay = 0, ease = easing.linear,
		onComplete = function()
		playSound("sounds/hitWood.mp3")
		circle:setAlpha(1.2)
		local timerDelayed = Timer.delayedCall(100, function() circle:setAlpha(1) end)
 
		if currentKnifeCount

SinisterSoft · May 2018

Nice looking game (the original).

Apollo14 · May 2018

SinisterSoft said:
Nice looking game (the original).

I also like it very much

Though I definitely don't wanna make yet another clone (there're plenty of them already)

I'm thinking about using this mechanics for a mini-game inside my main game.
Like daily challenge, or daily slots.

rrraptor · May 2018

Well, thats my version

Developed a few months ago.

There is my own VERY BASIC collision detection system, which is built on top of "SpartialHash" library. All it does is...checks for collisions

(just true or false)

It might be a bit complex to understand cuz no comments AT ALL

P.S. Use it however you want, i dont care.

rrraptor · May 2018

In my project, i'm rotating all knifes around the wheel (idk why i did it this way, probably becouse of the collision system), but alternatively you can remove knife from parent, then add to wheel container and translate coordinates using globalToLocal method, oh and dont forget to rotate the knife so it will be facing to center of the wheel.

------------------------------------
local dx, dy, w, h = application:getDeviceSafeArea(true)
 
ScreenW = w+math.abs(dx)
ScreenH = h+math.abs(dy)
 
stage:setPosition(dx, dy)
 
function CreateRect(w, h, ax, ay)
	h = h or w
	local p=Path2D.new()
	local ms="MHVHVZ"
	local mp={0,0, w, h, 0, 0}
	p:setFillColor(0, 1)
	p:setLineColor(0xffffff,1)
	p:setPath(ms,mp)
	if (ax and ay) then p:setAnchorPosition(w*ax,h*ay) end
	return p
end
 
function CreateCircle(r)
	local p=Path2D.new()
	local ms="MAAZ"
	local mp={-r,0, r,r,0,0,0,r,0, r,r,0,0,0,-r,0}
	p:setPath(ms,mp)
	p:setFillColor(0, 1)
	p:setLineColor(0xffffff,1)
	return p
end
------------------------------------
local tex = Texture.new("gfx/knipe.png", true)
local wheelRad = 130
local wheelY = 350
 
TestScene = Core.class(Sprite)
 
function TestScene:init()
	self.knifes = {}
 
	self:creteCircle()
 
	self:addEventListener(Event.ENTER_FRAME, self.update, self)
	self:addEventListener(Event.TOUCHES_BEGIN, self.touchBegin, self)
end
 
function TestScene:createKnife()
	local btm = Bitmap.new(tex)
	btm:setPosition(ScreenW / 2, ScreenH - 200)
	btm:setAnchorPoint(0.5, 0.5)
	btm:setRotation(-90)
	self:addChild(btm)
 
	return btm
end
 
function TestScene:creteCircle()
	local thick = 4
	self.circle = Sprite.new()
 
	local circle = CreateCircle(wheelRad)
	circle:setFillColor(0xDED6C0)
	circle:setLineThickness(thick)
	circle:setLineColor(0xAF685D)
	self.circle:addChild(circle)
 
	local ln = CreateRect(wheelRad - thick / 2, thick)
	ln:setFillColor(0xD1A579, 1)
	ln:setLineColor(0,0)
	self.circle:addChild(ln)
 
	self.circle:setPosition(ScreenW / 2, wheelY)
	self:addChild(self.circle)
end
 
 
function TestScene:addToCircle(k)
	k:removeFromParent()
	local ox, oy = k:getPosition()
	self.circle:addChild(k)
	local x, y = self.circle:globalToLocal(ox, oy)
	k:setRotation( k:getRotation() - self.circle:getRotation() )
	k:setPosition(x, y)
end
 
function TestScene:update(e)
	local dt = e.deltaTime
 
	self.circle:setRotation(self.circle:getRotation() + 45 * dt)
 
	for i = #self.knifes, 1, -1 do
		local k = self.knifes[i]
		local y = k:getY()
 
		y -= 500 * dt
 
		-- hit circle
		if (y < wheelY + wheelRad) then
			self:addToCircle(k)
			table.remove(self.knifes, i)
		else
			k:setY(y)
		end
	end
end
 
function TestScene:touchBegin(e)
	self.knifes[#self.knifes+1] = self:createKnife()
end

antix · May 2018

Here is a quick and messy solution which when the tween ends, uses setAnchorPosition() to set the knifes anchor position offset relative to where it would have hit the circle (kind of). Then it sets the knifes position to the circles position and every frame rotates it (like it does the circle). This gives the appearance that the knife is stuck to the circle.

setAnchorPosition() is a fantastic method that people often overlook

application:setBackgroundColor(0x2f3640)
centerX@240
centerY@427
local function playSound(sound) Sound.new(sound):play() end
 
--Add knives:
local knivesArr={}
for i=1,7 do
	knivesArr[i] = Bitmap.new(Texture.new("pics/knife.png",true))
	knivesArr[i]:setScale(0.3)
	knivesArr[i]:setAnchorPoint(0.5,0.5)
	knivesArr[i]:setPosition(centerX, centerY+250)
	stage:addChild(knivesArr[i])
	knivesArr[i]:setVisible(false)
end
currentKnifeCount=1
knivesArr[currentKnifeCount]:setVisible(true)
 
--Add circle:
local circle = Bitmap.new(Texture.new("pics/circle.png",true))
circle:setScale(0.5)
circle:setAnchorPoint(0.5,0.5)
circle:setPosition(240, 220)
stage:addChild(circle)
 
--Add apple to circle:
local apple = Bitmap.new(Texture.new("pics/apple.png",true))
apple:setScale(0.7)
apple:setAnchorPoint(0.5,0.5)
apple:setY(-325)
circle:addChild(apple)
 
local knives = {}
 
--Rotate circle every frame:
local function onEnterFrameFunc()
	circle:setRotation(circle:getRotation()+1)
 
	-- rotate all knives that have been thrown at circle
	for i = 1, #knives do
		local knife = knives[i]
		knife:setRotation(knife:getRotation() + 1)
	end
 
end
stage:addEventListener(Event.ENTER_FRAME, onEnterFrameFunc)
 
--Throw knife on tap:
local function throwKnife()
	playSound("sounds/throw.mp3")
	local knifeTween=GTween.new(knivesArr[currentKnifeCount], .15, {y = 410}, {delay = 0, ease = easing.linear,
		onComplete = function()
		playSound("sounds/hitWood.mp3")
		circle:setAlpha(1.2)
		local knife = knivesArr[currentKnifeCount] -- get the current knife
                knife:setPosition(circle:getPosition()) -- set knife to same position as circle
		knife:setAnchorPosition(knife:getWidth() * 0.5, -620) -- offset knifes anchor position
                knives[#knives + 1] = knife -- add it to knives to be rotated
 
		local timerDelayed = Timer.delayedCall(100, function() circle:setAlpha(1) end)
 
		if currentKnifeCount<7 then
			currentKnifeCount+=1
			knivesArr[currentKnifeCount]:setVisible(true)
		else print("Round finished") end
	end})
end
stage:addEventListener(Event.TOUCHES_END, throwKnife)

You could attach the knife directly to the circle with addChild() but you would have to take into account scaling and stuff.. or.. resize your graphics so they don't need to be scaled.

Apollo14 · May 2018

Wow! Both examples are awesome! So much stuff for me to learn! Thank you guys!

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Knife Hit mechanics - how to?

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