[BioC] marrayQuality & marray : empty ?

[Ghislaine Guigon]

hi,

I have a control column : "ctl" in gal file with control information, and I 
define maLayout like this :
         manip.layout <- 
read.marrayLayout(fname=file.gal,ngr=ngr,ngc=ngc,nsr=nsr,nsc=nsc,skip=skip, 
ctl.col = "ctl")
         x <-  as.character(maInfo(manip.gnames)[,"ctl"])
         y <- rep("probes", maNspots(manip.layout))
         y[x == "control"] <- "control"
         slot(manip.layout, "maControls") <- as.factor(y)

By this way, fonction maQualityPlots from the marrayQuality package creates 
DotPlots with control spots (in green) but not with empty spots.

How and where empty spots are they defined in the marray format ?

thanks