Sprite:getBounds(targetSprite)

GregBUG · September 2012

Hi! i've restarted at coding my collision system... for simple axis oriented collision
Sprite:getBounds(targetSprite) is very useful but i found a problem... (POSSIBLE BUG?)

The Problem
my sprite is 32x32px

if i scale x=2 and y=2 getBounds return width and height = 64 -> and is correct,
but
if i scale x=2 and y=1 getBounds return width = 64 (correct) and height (64) -> ERROR
it should be height = 32px?

i'm missing something or is a bug ?

@atilim i'm wrong ?

LUA CODE:

local ax, ay, ah, aw = self:getBounds(self.parent)
local bx, by, bh, bw = spriteB:getBounds(self.parent)

where (in my test code) self.parent is = "stage"

thanks,
Gianluca.

atilim · September 2012

Hi @GregBUG,

This simple example works as expected:

local sprite = Bitmap.new(Texture.new("box.png"))
stage:addChild(sprite)
print(sprite:getBounds(stage))
sprite:setScale(2, 2)
print(sprite:getBounds(stage))
sprite:setScale(2, 1)
print(sprite:getBounds(stage))

Here the output is:

0	0	80	80
0	0	160	160
0	0	160	80

Which version are you using? And can you post an example?

GregBUG · September 2012

@atilim

yes... my fault!!!

as you can see i swapped width and height

local ax, ay, ah, aw = self:getBounds(self.parent)
----------^^^^^^
local bx, by, bh, bw = spriteB:getBounds(self.parent)
------------^^^^^^
so my code not work!.

sorry... $:\$ ">

ahhh!!! 8-X

atilim · September 2012

hahaha.. Even though I've looked at your code to see "aw, aw" and "ah, ah", I've also missed that you swapped width and height

atilim · September 2012

As a side note, you can always use sprite:getBounds(sprite) to get untransformed bounds and transform as you wish.

GregBUG · September 2012

@atilim
yes sprite:getBounds(sprite) return the box that contain the sprite...
but if the sprite is rotated bound box size is increased... so if i transform transformation is not correct...

i mean... (getBounds in RED)

atilim · September 2012

sprite:getBounds(sprite) always returns the untransformed bounds:

local sprite = Bitmap.new(Texture.new("box.png"))
print(sprite:getBounds(sprite))
sprite:setRotation(45)
print(sprite:getBounds(sprite))

Output is

0	0	80	80
0	0	80	80

But you're correct about getWidth()/getHeight(). Because they return the transformed bounds. If the sprite is attached to a parent, getWidth()/getHeight() always return the same result with sprite:getBounds(sprite:getParent())

GregBUG · September 2012

ok.

but x and y are always 0

so the problem is when

local sprite = Bitmap.new(Texture.new("tntBox2.png"))
sprite:setPosition(160, 120)
sprite:setAnchorPoint(0,0)
stage:addChild(sprite)

print(sprite:getBounds(stage))
sprite:setRotation(45)
print(sprite:getBounds(stage))

now i get x and y coords, but w and h are wrong...

atilim · September 2012

Here x and y is 0 because I'm getting the bounds according to the sprite. But you're getting the bounds according to the stage. For example I've attached the screenshot of this example:

local sprite = Bitmap.new(Texture.new("box.png"))
sprite:setPosition(160, 120)
sprite:setScale(2, 1)
sprite:setAnchorPoint(0.3, 0.5)
sprite:setRotation(45)
stage:addChild(sprite)
 
local x, y, w, h = sprite:getBounds(stage)
 
local shape = Shape.new()
shape:setLineStyle(1, 0x000000)
shape:moveTo(x, y)
shape:lineTo(x + w, y)
shape:lineTo(x + w, y + h)
shape:lineTo(x, y + h)
shape:closePath()
shape:endPath()
 
stage:addChild(shape)

hmm.. Still I can't understand your point? ;;)

GregBUG · September 2012

no.. no.. you are right...

getBounds work fine...

but is not what i need....

i mean
when spirte is not rotated bBox returned is perfect (coincide with the sprites) so collision is perfect....

but when i rotate the sprite bbox is not what i need...

I thought that "getBounds" returned original bbox also when the sprite is rotated...
(i need the bbox of sprite angle = 0 then i rotate it according to the angle sprites so i get perfect oriented bBox) ...

sorry but my english is poor! and i don't know how to explain better

hgvyas123 · September 2012

@GregBUG
are u trying to say this

local bg = Bitmap.new(Texture.new("gfx/myBg.png"))
	bg:setPosition(512,384)
	self:addChild(bg)
	bg:setRotation(45)
 
	print(bg:getBounds(bg))--needs width and height from this
	print(bg:getBounds(stage)) -- needs x,y from this 
 
	bg:setRotation(0)
	print(bg:getBounds(bg))
print(bg:getBounds(stage))

output

0 0 1024 768 ----- width and height is perfect
-31.057983398438 384 1267.1353759766 1267.1352539062 ---x and y are perfect
0 0 1024 768
512 384 1024 768

atilim · September 2012

I think I understand now. Then you need to get untransformed bounds with sprite:getBounds(sprite) and transform as you wish. For example:

local x, y, w, h = sprite:getBounds(sprite)
x = x + sprite:getX()
y = y + sprite:getY()
w = w * sprite:getScaleX()
h = h * sprite:getScaleY()

So that you can get bounds independent of rotation. Maybe this is what you want?

Or get the untransformed bounds and move it to stage's coordinate system:

local x, y, w, h = sprite:getBounds(sprite)
local x1, y1 = sprite:localToGlobal(x, y)
local x2, y2 = sprite:localToGlobal(x + w, y)
local x3, y3 = sprite:localToGlobal(x + w, y + h)
local x4, y4 = sprite:localToGlobal(x, y + h)

atilim · September 2012

And one more question? Do you want to get oriented bounding box according to the stage? (OBBs are usually defined with 5 parameters: center x, center y, half width, half height and rotation)

GregBUG · September 2012

@hgvyas123 @atilim
thanks guys for help!

local x, y, w, h = sprite:getBounds(sprite)
x = x + sprite:getX()
y = y + sprite:getY()
w = w * sprite:getScaleX()
h = h * sprite:getScaleY()

this is what i need !

thanks!

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