cocos2d for iPhone

A fast, easy to use, free, and community supported 2D game engine

1. 

   par02
   Member

   I have read everything I could on Anchor Point and also w/ scaling. I still have no idea what is going on with a sprites position when you scale it.

   Its so weird. If you are a long way away from the Y axis, the horizontal positioning of the sprite is different on opposite sides of the Y axis.

   If my sprite is on the left side of the Y axis, it will reposition itself to the RIGHT of its pre-scaled position some distance I cannot figure out. The opposite is true when it is on the right side of the Y axis.

   Can someone please just help me decipher how scaling works w/ regards to a sprites positioning.

   The scenario is this:

   Sprite starts out w/ scale of 1.0f.
   Every frame I decrease the scale 0.01f until it reaches 0.5f (double the size). What should I change the sprites position to every frame to make up for the displacement of the anchor point due to scaling?

   Same goes with the opposite way. Start at 0.5f and increase the scale 0.01f every frame until it hits 1.0f.

   Thanks!

   PAR

   Posted 1 year ago #
2. 

   alter3cho
   Member

   There maybe better explanations but here's mine.

   If your sprite is an image of width = 4 and height = 4, then it's reference point for positioning is at width = 2 and height = 2 of the image (at center of the image) since the default anchor point is (0.5f, 0.5f) which is 4 * 0.5f = 2 and 4 * 0.5f = 2.

   So if you position this sprite at (0, 0), then the center of the image is positioned at that point.

   If you change the anchor point to (0, 0) then the positioning reference is at (0, 0) of the sprite (0 * 4 = 0, 0 * 4 = 0).
   So this sprite at (0, 0) then the bottom left corner of the sprite is at that position.

   Similarly scaling of 1.0f is the original size of the sprite. If you want to double it's size , then the scale should be set at 2.0f.
   If anchor point is at (0, 0) then sprite will grow or shrink from the bottom left corner of the image.

   Posted 1 year ago #
3. 

   par02
   Member

   Thank you for your reply.

   I guess I still dont understand why scaling makes the sprites "move". I am assuming its the anchor point but maybe thats not why they are moving?

   If I have a sprite with size 10x10 at position (25, 25) on the screen, when I scale it down or up, it moves around the screen. Why?

   Thanks!

   PAR

   Posted 1 year ago #
4. 

   crmagicxxx
   Member

   Anchor point is center of transformation. In cocos, anchor point is defined in relative coordinates (relative to node's width/height), so anchor (0.5,0.5) is at the center of the node, (1,0) is bottom/right, (0,0) is bottom/left, etc... So if your sprite moves with scale then its anchor, obviously, is not inside the sprite.

   Posted 1 year ago #
5. 

   par02
   Member

   Ok I still dont understand "why" what I was doing didnt work BUT, I figured out a different way to do things.

   Before, I was actually scaling each individual sprite. Now, Im just scaling the layer and everything is scaling perfectly.

   Thanks for the replies!

   PAR

   Posted 1 year ago #

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