Re: [Dev-luatex] Q: Can LuaTeX produce xdv?

2009/1/4 Jonathan Fine :

Martin Schröder wrote:

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2009/1/2 Jonathan Fine :

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Please could I be told, what are the main benefits of directly producing PDF?

Reasoning about and manipulating included PDFs. This is much harder with a two-pass engine like XeTeX + postprocessor; as an example compare the knowledge of XeTeX (the program) and pdfTeX about included PDFs.

I'm sorry, but I don't understand.

I think you do. :-)

I'll invent an example (so it's not really an example). We wish to resize an image to fit the measure, but if it's a bitmap image we want to choose a scaling factor that works well with our planned output device. Here's another. We want to know if the image contains colour, because if it does it should appear in the colour plates section.

In both cases we have to open the image file and, as you say, reason about it. Based on this reasoning we come to a conclusion (such as a scale factor) and both 9a) typeset the text and (b) process the image accordingly.

LuaTeX does (a) and (b) at the same time. I see no reason why a 'special' that says 'do (b)' should not be written to the xdv or whatever output file.

A special makes that harder; it needs more code. The backend needs the code for reasoning about the image anyway; now the frontend also needs it. You're duplicating code. And you need code for the two parts to communicate. More code means more errors. Consider this example: I want to include PDFs with layers and want to mix layers generated by the document with layers from the PDFs, controlled by the document. This might be doable in two passes, but it is much easier in one pass.

[Discussion of performance snipped]

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But as I said: Show us your code.

Well, it's not MY code, but I'm sure you're welcome to use it:

You don't understand, so I'll be more clear: Shut up and code! :-) You seem to be the only one here interested in this mythical luatex + xdv, so why don't you SHOW us what it can do better? I can see only ONE benefit from your mythical xdv: interchangable backends. But I don't think the team finds *dvipdfm* so much more interesting than luaTeX. Best Martin