SetWorldTransform and XFORM: help with positioning a rotated image

Recently I took back an old drawing app created in VB6 some years (:cry:) ago to add a few mods, just for my entertainment. I'm pretty satisfied with the result: now I have a rich set of primitives to draw and, this is the best, I can now fill every geometry with a scaled image.
There is only a SMALL problem that I can not fix, surely for my ignorance about GDI: when I rotate a geometry by an arbitrary angle (let say a square by 30 degrees), the included picture should rotate itself too still filling then inside.
I found some usefull articles on image rotation using XFORM, SetGraphicsMode and SetWorldTransform.
Everything is fine: in a test program I got the images rotated as I want...but the positioning of the image is not correct.

I assume that a short explanation of my procedures could help in identify the problem:
I have a PictureBox (called 'pic) as a screen where to draw (autoredraw=false)
A custom structure is filled with the 'object(s)' parameters (geometry, size, positiong, colors...).
Among these there are the 2 important info: the picture filename,if exists, and an empty DIB (cDIBclass) where, when needed, I store the sampled image. In this way the screen redraw is really fast since I just have to BitBlt from the DIB to screen; no reload or resample needed.
Every object has a number of PointAPIs to describe the geometry.
In the Redraw I create a Region on the screen (CreatePolygonRgn), draw the frame with FrameRgn and fill the interior with a solid color (FillRgn) OR Clip the region and then BitBlt the image IF the shape is not rotated, otherwise I call this Rotate procedure.

Code:

---

  If .objRot Then
      Call Rotate(pic, ob, .objRot)
  Else
      BitBlt pic.hDC, objX, objY, objW, objH, .objDIB.hDC, 0, 0, vbSrcCopy
  End If

---

This is the main part of the routine:

Code:

---

Public Sub Rotate(dst As PictureBox, obIndex As Long, degrees As Long)
  objX = .objRect.Left 'shape position
  objY = .objRect.Top
  objW = .objRect.Right - .objRect.Left  'shape size
  objH = .objRect.Bottom - .objRect.Top
  dx = objW / 2
  dy = objH /2
  ...
    nGraphicsMode = SetGraphicsMode(dst.hDC, GM_ADVANCED)
    mtx.eM11 = cosAng
    mtx.eM12 = -sinAng
    mtx.eM21 = sinAng
    mtx.eM22 = cosAng
    mtx.eDx = dX      'translate the rotation point
    mtx.eDy = dY      'to the middle of our destination
    SetWorldTransform dst.hDC, mtx
    BitBlt dst.hDC, objX, objY, objW, objH, .objDIB.hDC, 0, 0, vbSrcCopy
  ...
  cleanup

---

Where 'dst' is pic, the screen PictureBox.

This routine does its job, but the rotated image does not center and fill the shape.
I tried different combinations for dX and dY (0,0 ; object Top-Left; ...) and for the destination parameter in the BitBlt (objW, objH ; 0,0; center of shape...); no success.
I'm sure I'm doing wrong with the highlited setting; please help me.

Here is an example of what I get (the best result):
Attachment 193891
Attachment 193890