objective c - how to change the alpha of a groundoverlay in google maps ios sdk? -


i added groundoverlay mapview, , found thoese ways change alpha of groundoverlay.icon. how set opacity/alpha of uiimage? seems has no affect in app, still can not see map or other groundoverlays behind image. there solution handle this?

+ (uiimage *) setimage:(uiimage *)image withalpha:(cgfloat)alpha

{

// create pixel buffer in easy use format cgimageref imageref = [image cgimage]; nsuinteger width = cgimagegetwidth(imageref); nsuinteger height = cgimagegetheight(imageref); cgcolorspaceref colorspace = cgcolorspacecreatedevicergb();  uint8 * m_pixelbuf = malloc(sizeof(uint8) * height * width * 4);  nsuinteger bytesperpixel = 4; nsuinteger bytesperrow = bytesperpixel * width; nsuinteger bitspercomponent = 8; cgcontextref context = cgbitmapcontextcreate(m_pixelbuf, width, height,                                              bitspercomponent, bytesperrow, colorspace,                                              kcgimagealphapremultipliedlast | kcgbitmapbyteorder32big);  cgcontextdrawimage(context, cgrectmake(0, 0, width, height), imageref); cgcontextrelease(context);  //alter alpha int length = height * width * 4; (int i=0; i<length; i+=4) {     m_pixelbuf[i+3] =  255*alpha; }   //create new image cgcontextref ctx = cgbitmapcontextcreate(m_pixelbuf, width, height,                                          bitspercomponent, bytesperrow, colorspace,                                          kcgimagealphapremultipliedlast | kcgbitmapbyteorder32big);  cgimageref newimgref = cgbitmapcontextcreateimage(ctx); cgcolorspacerelease(colorspace); cgcontextrelease(ctx); free(m_pixelbuf);  uiimage *finalimage = [uiimage imagewithcgimage:newimgref]; cgimagerelease(newimgref);  return finalimage;

}


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