Add an accessor to get the offset of a subsetted BitmapDevice

Change-Id: I8a4a588287a90c6953b367bb02e075ea58f13a96

basebmp/inc/basebmp/bitmapdevice.hxx

@@ -92,6 +92,13 @@ public:
      */
     bool isTopDown() const;
 
+    /** Query the offset from the start of the memory buffer
+
+        @ return the offset, which is (0,0) unless this is a subset
+        device.
+    */
+    basegfx::B2IVector getOffset() const;
+
     /** Query type of scanline memory format
      */
     sal_Int32 getScanlineFormat() const;

basebmp/source/bitmapdevice.cxx

@@ -1105,6 +1105,11 @@ bool BitmapDevice::isTopDown() const
     return mpImpl->mnScanlineStride >= 0;
 }
 
+basegfx::B2IVector BitmapDevice::getOffset() const
+{
+    return basegfx::B2IVector(mpImpl->maBounds.getMinX(), mpImpl->maBounds.getMinY());
+}
+
 sal_Int32 BitmapDevice::getScanlineFormat() const
 {
     return mpImpl->mnScanlineFormat;