HARD Question : Z position impact on stage position

[Rainman4500]

I have a sprite that I zoom out using the sprite.z property. Once the z property has been modified the sprite x and Y values do not match the stage x and y real value. So far so good and what I was expecting!

What I want to accomplish is that when the user clicks the stage the sprite tweens to where the mouse was clicked but I don't know what x and y position to send to the sprite. ( since stage 200,200 is something like 400,400 for the sprite depending on z value)

I tried Utils3D.projectVector using Matrix3D of the perspectiveProjection of the stage without success. (i.e. I get Vector3D(Infinity, Infinity, NaN))

Any pointers?

I could fallback to scalex/scaley but sprites.z gives me the correct scale, perspective projection, paralax scrolling since I have sprites on different z level all for free. I would have to recode all that.

[Rui Silva]

Hi,

I haven't played around with the z axis a lot, but have you tried the localToGlobal3D and globalToLocal3D methods?

Cheers,

Rui.

[Rainman4500]

Boy I feel I'm close with globalToLocal3D!

Unfortunatly the more the sprite if far on the z axis the more the result is offset by many pixels either left or right.

[Kenneth Kawamoto]

Well, I tested my script and it works just fine no matter what number you set for z

[Rainman4500]

I will have to give you reason since if I use :

a- Your code

b- GlobalToLocal3D

c- Sprite.MouseX / MouseY

I get the same X,Y values but with an offset so the problem must be with me and my Stage setup.

Great Thanks!

[Kenneth Kawamoto · Accepted solution]

This is an interesting one

The formula to obtain the x coordinate on the screen from a point in 3D space is:

screen x = point x * (distance to screen / distance to point z)  

So, to obtain the 3D point x from the screen x, you'd do:

point x = (screen x * distance to point z) / distance to screen

Translating this to AS3, you'd get:

...
       private function moveObjectTo3DFrom2D(object:DisplayObject, vX:int, vY:int):void {
            var cX:Number = root.transform.perspectiveProjection.projectionCenter.x;
            var cY:Number = root.transform.perspectiveProjection.projectionCenter.y;
            var f:Number = root.transform.perspectiveProjection.focalLength;
            with(object){
                x = cX + ((f + object.z)*(vX - cX))/f;
                y = cY + ((f + object.z)*(vY - cY))/f;
            }
        }
...