Negative/Positive printing support

I was thinking what a great thing should be to see printing support in FlatCAM.

The reason for this feature request is that for those of us that we use the dry film UV exposure method of doing PCB's (the negative dry film is very cheap on Aliexpress and give a high quality PCB), having a way to get an transparent film with the pattern (negative or positive depending of the used photosensitive film) printed on it, is a must.

I like how the Gerber look in FlatCAM and I will be very happy to see that I can obtain a PDF file with the pattern on it, along the G-Code for drilling the holes (which is already in FlatCAM).

In FlatCAM, we should be able to create a "special" rectangle around all the pattern that needs to printed (negative or positive) and then print that as it is (in PDF directly or using a PDF virtual printer) for the positive print or printing an color inverted version for the negative print.

That rectangle is useful for negative printing since we don't want to end up with an A4 (letter) page full of black outside the pattern. I marked the rectangle as "special" because it should be ignored in the geometry processing and should be used only for printing. Maybe a good name should be a "Print Select Geometry" rectangle.

The trick is to get the print as close to the real distances found in the Gerber file, and not actually what is on the screen (this may be zoomed). Of course the physical printer add some error on the print and an option to scale on the X axis and/or Y axis is even better. But one step at the time.

JP, given how FlatCAM is working, do you think it is possible to add such a feature? Negative printing is what I am mostly after ... but there could be other usages e g printing a template before the actual router work (in case of a FlatCAM made geometry).

Again, thank you very much for your work!

Best, Marius

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