option to use named SpotColor

[Crowdedlight]

I have an application where I need to use a named spotcolor with the name "Cut". As the printer requires that to cut the right lines.

It seems like this library makes spotcolours behave like CMYK colours and does not give an option to name it?

Would it be something that could be added?

I would consider looking into implementing it myself, but would need some pointers on how the library currently exports the spotcolor to pdf. Unsure if it already handles the custom colorspace for spotcolors and is just missing the naming, or it sees spotcolors as CMYK like the CMYK color and would need to figure out how to implement spot colours related to PDF specification.

[fschutt]

To be fair, I haven't worked with spot colors. The library just converts them into a Stream of lopdf::Operation:

printpdf/src/color.rs

Lines 22 to 52 in fbc7d69

	fn from(val: PdfColor) -> Self {
	use lopdf::Object::*;
	// todo: incorporate ICC profile instead of just setting the default device cmyk color space
	let (color_identifier, color_vec) = {
	use self::PdfColor::*;
	match val {
	FillColor(fill) => {
	let ci = match fill {
	Color::Rgb(_) => OP_COLOR_SET_FILL_CS_DEVICERGB,
	Color::Cmyk(_) | Color::SpotColor(_) => OP_COLOR_SET_FILL_CS_DEVICECMYK,
	Color::Greyscale(_) => OP_COLOR_SET_FILL_CS_DEVICEGRAY,
	};
	let cvec = fill.into_vec().into_iter().map(Real).collect();
	(ci, cvec)
	}
	OutlineColor(outline) => {
	let ci = match outline {
	Color::Rgb(_) => OP_COLOR_SET_STROKE_CS_DEVICERGB,
	Color::Cmyk(_) | Color::SpotColor(_) => OP_COLOR_SET_STROKE_CS_DEVICECMYK,
	Color::Greyscale(_) => OP_COLOR_SET_STROKE_CS_DEVICEGRAY,
	};
	let cvec = outline.into_vec().into_iter().map(Real).collect();
	(ci, cvec)
	}
	}
	};
	Operation::new(color_identifier, color_vec)
	}

here, when you call set_fill_color, it calls Operation::from:

printpdf/src/pdf_layer.rs

Line 133 in fbc7d69

self.add_operation(PdfColor::FillColor(fill_color));

So idk, maybe spot colors need different handling. I haven't read the PDF reference on this topic.

[fschutt]

You could create an API like this:

PdfDocument::create_named_spotcolor(&mut document, ...) -> SpotColorRef { }

enum PdfColor {
   ...
   NamedSpot(SpotColorRef),
}

impl From<SpotColorRef> for lopdf::Operation {
  fn from(s: SpotColorRef) -> { 
      lopdf::Operation::Reference(PDF_FILL_COLOR, Object::Reference(s.inner.clone())) 
  }
}

https://docs.rs/lopdf/latest/lopdf/enum.Object.html

[Crowdedlight]

Thanks for the pointers!

I will have a look at it and see if I can get it working. Seems like a good way to go about it.

[TheOriginalAyaka]

Any updates on this?

[Crowdedlight]

Any updates on this?

Sorry, priority work came in, so I had to put my attempt on the backburner. I solved my issue here and now by opening the generated pdf in illustrator and manually set it to spot color. I hope to get some time in coming months to give it a go.