+// wxAlphaBlend: our fallback if ::AlphaBlend() is unavailable
+#ifdef wxHAVE_RAW_BITMAP
+
+static void
+wxAlphaBlend(HDC hdcDst, int xDst, int yDst, int w, int h, int srcX, int srcY, const wxBitmap& bmpSrc)
+{
+ // get the destination DC pixels
+ wxBitmap bmpDst(w, h, 32 /* force creating RGBA DIB */);
+ MemoryHDC hdcMem;
+ SelectInHDC select(hdcMem, GetHbitmapOf(bmpDst));
+
+ if ( !::BitBlt(hdcMem, 0, 0, w, h, hdcDst, 0, 0, SRCCOPY) )
+ {
+ wxLogLastError(_T("BitBlt"));
+ }
+
+ // combine them with the source bitmap using alpha
+ wxAlphaPixelData dataDst(bmpDst),
+ dataSrc((wxBitmap &)bmpSrc);
+
+ wxCHECK_RET( dataDst && dataSrc,
+ _T("failed to get raw data in wxAlphaBlend") );
+
+ wxAlphaPixelData::Iterator pDst(dataDst),
+ pSrc(dataSrc);
+
+ pSrc.Offset(dataSrc, srcX, srcY);
+
+ for ( int y = 0; y < h; y++ )
+ {
+ wxAlphaPixelData::Iterator pDstRowStart = pDst,
+ pSrcRowStart = pSrc;
+
+ for ( int x = 0; x < w; x++ )
+ {
+ // note that source bitmap uses premultiplied alpha (as required by
+ // the real AlphaBlend)
+ const unsigned beta = 255 - pSrc.Alpha();
+
+ pDst.Red() = pSrc.Red() + (beta * pDst.Red() + 127) / 255;
+ pDst.Blue() = pSrc.Blue() + (beta * pDst.Blue() + 127) / 255;
+ pDst.Green() = pSrc.Green() + (beta * pDst.Green() + 127) / 255;
+
+ ++pDst;
+ ++pSrc;
+ }
+
+ pDst = pDstRowStart;
+ pSrc = pSrcRowStart;
+ pDst.OffsetY(dataDst, 1);
+ pSrc.OffsetY(dataSrc, 1);
+ }
+
+ // and finally blit them back to the destination DC
+ if ( !::BitBlt(hdcDst, xDst, yDst, w, h, hdcMem, 0, 0, SRCCOPY) )
+ {
+ wxLogLastError(_T("BitBlt"));
+ }
+}