MicroGDS allows you to choose, when printing, whether to use "Black and white" mode. The effect of this mode is to produce output as if all the following colours were black
Exceptionally, the colours of a gradient fill stroke are not changed.
Note however
The rationale for this mode is that it is common, when producing a drawing intended for printing on a black and white printer, to use colours as a user interface hint (e.g. furniture is displayed in red). If such colours are sent to a black and white printer, then the printer will convert even solid colours (e.g. pure red) to shades of grey, by a method chosen by the printer driver. This is probably not what is wanted.
On the other hand it is also common, when producing a drawing intended for printing on a colour printer, to want to produce a check-plot on a black and white printer. Under these circumstances having the printer driver convert colours to shades of grey is the best thing to do.
MicroGDS 9 therefore lets you choose, on a window by window basis, whether the default behaviour is for printing to happen in black and white mode, or in colour. This is done by checking or unchecking the menu entry View>Black and White when Printed (and then going View>Save View if you want the change to persist).
The main effect of this new option is to preset the "Black and white" checkbox on the print dialog when it is summoned — when you give the print command for a window this checkbox will initially match the window's "View>Black and White when Printed" state. You can, of course, change the setting on the print dialog before pressing "OK", but such a change persists for a single print command only.
When printing is done from the API, the story is a little more complicated...
If you print in black and white mode to a colour printer, you may be surprised by the results. Much of the drawing will appear in black and white as you might expect, but gradient fills, colours from materials, and raster and Ole primitives will appear in colour. This is sometimes what's wanted: it's not uncommon for documents to be basically black and white, but with (say) colour photographs.
In any case, converting MicroGDS output to shades of grey ourselves when printing in black and white mode would be impractically difficult for Ole and raster photos. It would, in principle, be possible to convert materials and gradient fills to grey ourselves, but then we'd also run the risk of greyscale conversion inconsistencies when when printing to a monochrome printer. If you had a red raster photo (which the printer converts to grey in a device specific manner) next to a red material (which we had converted to grey in a device independent manner), they might appear differently on the print.
If you wish to produce genuinely greyscale output, perhaps to produce a "black and white" print when the only available printer is a colour printer, then you must adjust the printer's own properties to operate in a black and white mode. How this is done varies from printer to printer, but most colour printers seem to provide such a setting.
When exporting a window to a raster format you are given three choices:
If the window is marked as Black and White when Printed then the export dialog will default to Force all colours to black, otherwise it will default to Colour. As with printing, you are at liberty to change this setting, such a change persists for a single command only.