imagemagick composite in c language

in c language, use imagemagick library.

i wanna to composite two image.

but don't set gravity, not error. wrong position "play btn" image T.T

if ( watermark_image_info->gravity > 0 && watermark_image_info->gravity < 10 ) {
     MagickSetGravity(image->wand, NorthEastGravity);
 }

if( MagickCompositeImage( image->wand, watermark_image->wand, OverCompositeOp, watermark_image_info->offset_x, watermark_image_info->
offset_y ) == MagickFalse ) {
     fprintf( stderr, "MagickCompositeImage error\n");
     return NULL;
 }