Scaling sprite around some point

Mplius

Hello,
I have a problem with image/sprite/layer scaling around some particular point.
1) I have a map loaded from tiled and added to scene
2) I want some functionality with two fingers. I already implemented scrolling/moving with two fingers. Now I want scaling.

For moving map, what I do, I calculate starting coordinates of the center between two fingers and I update accordingly.

Now I have a problem. I want to scale the map around the point between my two fingers. If I use simple sprite:setScale(n), it scales, however it scales around top/left corner.

Now my question. Is there a special function to set scaling point? Or should I use some math, to move map accordingly?

P.S. My first post here, so some random thoughts. I'm totally in love with Gideros. I came here from love2d background, was missing mobile development features. Getting used to everything bit by bit. Cheers.

Mells

Hi @Mplius and welcome here.
The answer would be to use setAnchorPoint() but this is not available for sprites, however a community built library aims to fill the need.
Please try this (implementation of setanchorpoint for Sprites) and see if it helps.

Mplius

Hmmm. I've checked GiderosCodingEasy mini library, and it looked good. However, to use 2000+ code lines for simple scaling seemed a bit overkill. I've checked more, and found this http://giderosmobile.com/forum/discussion/1502/setanchorpoint-for-sprites-shapes-and-all-of-your-classes implementation. It looked great, since it's small and basically does same thing.
However. I've reached a huge performance drop.
I am doing something like this:
currentMap:setAnchorPoint(0.5, 0.5)
currentMap:setScale(scale, scale)
currentMap:setAnchorPoint(0, 0)
each time I want to scale.
And my frames drops from hundreds to 3-4. I am using ipod touch 2.5G for tests.
I tried to make scaling gradual, for example, to scale only if I move more than 64 pixels. Same thing. I don't want scaling to be sluggish, I want smooth and eye-candy effect

I am testing on 16x16 isometric map with two layers. Doesn't seem like too much sprites, no?

What i thought about, maybe I could use Sprite:setMatrix(matrix) function, maybe it would be faster? However, I lack in math a bit, to make optimal calculations.

P.S. without AnchorPoint library, when scaling I get ~15 frames. Well, acceptable, I guess. With only setting anchor points (no scaling), FPS drops to ~7.
Maybe I should change whole scaling idea to some slidebar...

Cyberience

Yep I am having similar issues, if I was pting an image on a canvas in HTML5 I would use (locationx, locationY, width, height) and it would stretch or shring the image to fit.

Any ideas?

ar2rsawseen

@Mplius just for test, is there the same performance drop with GiderosCodingEasy? Just for test, if now, you could separate the code you need. If yes, then I guess it would be really hard to get it more efficient in pure Lua.

@Cyberience how is this related?

zaniar

how about this?

sprite:setMatrix(Matrix.new(scale, 0, 0, scale, - scale * rotationPointX+ rotationPointX, - scale * rotationPointY + rotationPointY ))

Cyberience

Wow thats deep.
Do you have a little more code around it to show the values and how an image is represented, zoomed in or out?

ar2rsawseen

Another interesting solution might be creating another parent and positioning child with -halfwidth/-halfheight offset to get 0.5, 0.5 I think it would work in most cases, wouldn't it?