Bump

misterhup

Hi! I am trying to detect a simple collision between 2 bitmaps and then do something if they do collide. I am thinking to use bump, so I was wondering if it handles bitmaps and/or other types of objects. (for example I have an objected imported using Spriter, and I was wondering if I can detect a collision with it).
Also I tried detecting collisions with the following code, but the response is way to slow for what I need so I was wondering if bumb can do any better.

function Sprite:collision(sprite2) local myX = self:getX() local myY = self:getY() local myWidth = self:getWidth() local myHeight = self:getHeight() local otherX = sprite2:getX() local otherY = sprite2:getY() local otherWidth = sprite2:getWidth() local otherHeight = sprite2:getHeight()   if myY + myHeight < otherY or myY > otherY + otherHeight then return false end   if myX > otherX + otherWidth or myX + myWidth < otherX then return false end   return true end

ar2rsawseen

You can try this, should be faster:

function Sprite:collidesWith(sprite2) local x,y,w,h = self:getBounds(stage) local x2,y2,w2,h2 = sprite2:getBounds(stage)   return not ((y+h < y2) or (y > y2+h2) or (x > x2+w2) or (x+w < x2)) end

misterhup

Thanks! The difference is visible and it works way faster but I think I discovered something. I check for collision with a sprite which is rotated but I think it detects the collision with the previous position of the sprite so the collision is made with the unrotated object...Changing the rotation of an object shouldn't change it's position too?

misterhup

What I'm trying to say is should this function work with a rotated sprite?

chuz0

I think that it only works on x-axis aligned boxes.
There's another function that tells you whether a point is inside a box or not, so you can check the 4 points of a rotated box and check if any of them is inside the other box.

ar2rsawseen

yes, this approach uses bounding box and I think bounding box of rotated sprite is just a figure that can include the rotated sprite.

So it won't work in those cases

misterhup

So, is there any other way to check for collision with a rotated object?

misterhup

I could write a function and create an invisible sprite to rotate and resize on the axis based on the rotation of the main sprite, and use that main sprite just as graphic and not as a collision object. But I fear that would impact the performance of the app a lot.

antix

@misterhup, bump only works with AABB's (Axis Aligned Bounding Boxes) so you can't use it for rectangles that have been rotated.

Are you needing to detect collisions with rotated rectangles?

misterhup

@antix Sadly yes... And even more, rotated sprites/imported objects. Is there any way I can do that? Box2D maybe?

antix

@misterhup, okay box2D is one way to solve your collision issue but it is kind of like hitting an ant with a sledgehammer

misterhup

Well is there any better way to do it then? I just want to detect collision between 2 rotated sprites. That's all. :-/

ar2rsawseen

There was also TNT collision engine.

But about Sprite implementation, I remember there were hacks, like transforming coordinates yourself, or using your own sprite local bounds and transforming coordinates to global.

Theoretically it could work, but not 100% sure

This thread could help you:
http://giderosmobile.com/forum/discussion/1733/spritegetboundstargetsprite/p1

antix

Okay here is a little example project that can detect collisions between rotated rectangles. The collision stuff is from this page.. https://bitbucket.org/RudenkoPaint/sat-lua. The version included here has been modified slightly to better work with Gideros. It's a bit messy but it works.

When you run the example project you can click and drag one of the boxes around. If it collides with the other, both turn red.

NOTE: The example is fairly basic and does not perform any collision resolution but with a bit of work it could easily do so. The "response" table in the main loop contains pretty much everything you need to resolve the collisions.

Anyway, it should be enough to get you up and running

EDIT: See further down the thread for the latest version of the example

antix

I am just tidying up the SAT code and will post it in a few days as we are off for Easter weekend now and most likely will have no internet (

misterhup

Thanks a lot! I got it to work Also I found a way to do it using a bunch of rectangles positioned on the sprites axis and checking the collision with every one of them. It is a little too grindy and your method is better in my opinion, so Ill go with it :P Ill post my method here anyways after I optimize it a little.

antix

As promised, I have updated the example...

--[[   SAT Rectangle Collision Example for Gideros by Cliff Earl Antix Software March 2016   Example project that creates and displays 2 rotating boxes that can be dragged about the screen by their center points, and detects collisions between them.   Collision detection is a 2 part process. First the bounding boxes are checked to see if they overlap (it is pointless to waste CPU time on SAT calculations unless that is the case). Once the boxes overlap they will be tinted yellow and SAT collision detection will then be applied to test for intersection (one rectangle partially inside the other rectengle). If the rectangles do intersect then they will be tinted red.   There is one class (Draggable) and 1 library (GSAT) included in the example.   Draggable An extension of Bitmap that can be dragged about by its center. See Draggable.lua for more information.   GSAT A simple library for performing collision detection (and projection-based collision response) of rectangular shapes in 2 dimensions. See GSAT.lua for more information.   --]]   --require("mobdebug").start() -- ONLY REQUIRED FOR ZEROBRANE   local GSAT = require("gsat") -- THE COLLISION LIBRARY   local function newBox(actor) -- CREATE A NEW COLLISION BOX local x, y, w, h = actor:getBounds(stage) local box = GSAT.Box(x + (w * 0.5), y + (h * 0.5), w, h) box:setRotation(actor:getRotation()) return box end   local function actorInActor(actor1, actor2) -- TEST 2 BOUNDING BOX FOR OVERLAP local x, y, w, h = actor1:getBounds(stage) local x2, y2, w2, h2 = actor2:getBounds(stage) return not ((y+h < y2) or (y > y2+h2) or (x > x2+w2) or (x+w < x2)) end   local info = TextField.new(nil, "Drag the boxes by their centers to move them") info:setPosition(20, 20)   local player = Draggable.new(Texture.new("images/box.png", true), {x = 160, y = 128}) -- CREATE PLAYER player.box = newBox(player) player.onDragged = function() player.box:setPosition(player:getPosition()) end   local enemy = Draggable.new(Texture.new("images/box.png", true), {x = 160, y = 352}) -- CREATE ENEMY enemy.box = newBox(enemy) enemy.onDragged = function() enemy.box:setPosition(enemy:getPosition()) end   local function onEnterFrame(event) -- MAIN LOOP   local angle = enemy:getRotation() - 0.284 -- ROTATE ENEMY CCW enemy:setRotation(angle) enemy.box:setRotation(angle)   angle = player:getRotation() + 0.284 -- ROTATE PLAYER CW player:setRotation(angle) player.box:setRotation(angle)   if actorInActor(player.box, enemy.box) then stage:setColorTransform(1, 1, 0, 1) -- BOXES OVERLAP, TINT YELLOW   local response = GSAT.Response() -- CHECK FOR COLLISION BETWEEN BOXES local collided = GSAT.checkCollision(player.box, enemy.box, response) if collided then stage:setColorTransform(1, 0, 0, 1) -- BOXES COLLIDED, TINT BOXES RED   -- -- PERFORM COLLISION RESOLUTIONS HERE --   end else stage:setColorTransform(1, 1, 1, 1) -- NO COLLISION, TINT BOXES BACK TO NORMAL end   end   stage:addEventListener(Event.ENTER_FRAME, onEnterFrame)   stage:addChild(enemy) stage:addChild(player)   stage:addChild(info)