Re: Area tree - renderer (pr.fo for structure renderers)
On Saturday 16 March 2002 14:52, Peter B. West wrote: . . . The last stage of the FOP process translates one page description (the area tree) into another (the input to the target renderer.) ok So why would anyone want to interpose another translation step into this tightly coupled arrangement? Who knows? . . . For page-based renderers where FOP has to compute the layout (like for PDF output), I don't see a need for another translation step either. IMHO asking who knows is usually a sign that a feature is not needed *at this stage of development*... OTOH, for structure-based renderers like RTF and MIF, I think the only parts of FOP that are reusable are the first two stages: parsing and property resolution (apart from infrastructure like logging, config, etc. which might come from Avalon in the future?). Last week we had a talk about using XML to communicate between FOP pipeline components, but for me this currently would only make sense between the property resolver and structure renderers components. The deal is being able to reuse FOP's property resolution (p.res) in different contexts. I think the following usage scenarios could greatly benefit from reusing FOP's front-end (parser + p.res). In the following I call pr.fo an XSL-FO document where all properties (fonts, sizes, etc.) are explicitely written, for example when inherited from parents: a) XSL-FO to RTF conversion: FOP parser - FOP p.res - pr.fo - jfor converter b) XSL-FO to MIF conversion FOP parser - FOP p.res - pr.fo - yet-to-write XML-to-MIF converter c) automated testing of first FOP stages FOP parser - FOP p.res - pr.fo - XML testing tool Keeping in mind that RTF and MIF are formats where the page layout is left to the client software to compute (word processor or FrameMaker), keeping these converters independent of FOP instead of integrating them has several advantages: b) Helps keep FOP focused on its main task: generating great PDF from XSL-FO documents c) If FOP is ever rewritten in another language for performance, these converters, being much less compute-intensive, can stay in java and keep the same interface to the FOP components that they use d) assuming I want to write a MIF converter, basing it on XSL-FO input instead of on a FOP API allows me to easily include MIF-specific constructs for applications where XSL-FO conformance is not needed but precise control of the generated MIF is (often a requirement for MIF when producing half-finished documents that are typographically reviewed before printing). In conclusion, I think an interface based on XML documents (possibly this pr.fo discussed above) is the best choice to use between the FOP property resolution stage and the structure renderers like RTF and MIF renderers. OTOH I agree that using XML between the layout and rendering stages doesn't make sense at this stage of FOP development. Due to many other commitments, I don't have time right now (sorry, I know you're getting used to hear this) to implement this pr.fo interface, but if we agree on its usefulness I'll put this high on my list and hopefully give it a shot in the next few weeks... -- Bertrand Delacrétaz (codeconsult.ch, jfor.org) buzzwords: XML, java, XSLT, cocoon, mentoring/teaching/coding. disclaimer: eternity is very long. mostly towards the end. get ready. - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, email: [EMAIL PROTECTED]
Re: Area tree - renderer (pr.fo for structure renderers)
Bertrand, See below... Bertrand Delacretaz wrote: On Saturday 16 March 2002 14:52, Peter B. West wrote: . . . The last stage of the FOP process translates one page description (the area tree) into another (the input to the target renderer.) ok So why would anyone want to interpose another translation step into this tightly coupled arrangement? Who knows? . . . For page-based renderers where FOP has to compute the layout (like for PDF output), I don't see a need for another translation step either. IMHO asking who knows is usually a sign that a feature is not needed *at this stage of development*... This was purely for rhetorical effect. My point, developed further in the original, was that shoe-horning an xml-based externalisation step in here is probably completely redundant. You have to invent a method of expressing all of the information contained in the area tree, while flattening the tree into a series of drawing instructions. If you need to externalise the area tree, why not externalise it using an already well-defined page description language. Your externalisation is then Area Tree - Well defined PDL Then attach any translators that you like to the end of that PDL; PDL - PDF, PDL - awt, PDL - PCL, whatever. By the stage of the translation to the PDL, XSLFO has done its work. If someone wants to define a PDL in XML, fair enough; but he has fallen off the end of the spec, and is creating something new. At least that's the way I see it. And if you want an already well-defined PDL, with, I assume, a number of converters already in place, why not Postscript? Maybe even PDF. OTOH, for structure-based renderers like RTF and MIF, I think the only parts of FOP that are reusable are the first two stages: parsing and property resolution (apart from infrastructure like logging, config, etc. which might come from Avalon in the future?). Last week we had a talk about using XML to communicate between FOP pipeline components, but for me this currently would only make sense between the property resolver and structure renderers components. The deal is being able to reuse FOP's property resolution (p.res) in different contexts. I think the following usage scenarios could greatly benefit from reusing FOP's front-end (parser + p.res). In the following I call pr.fo an XSL-FO document where all properties (fonts, sizes, etc.) are explicitely written, for example when inherited from parents: a) XSL-FO to RTF conversion: FOP parser - FOP p.res - pr.fo - jfor converter b) XSL-FO to MIF conversion FOP parser - FOP p.res - pr.fo - yet-to-write XML-to-MIF converter c) automated testing of first FOP stages FOP parser - FOP p.res - pr.fo - XML testing tool Keeping in mind that RTF and MIF are formats where the page layout is left to the client software to compute (word processor or FrameMaker), keeping these converters independent of FOP instead of integrating them has several advantages: b) Helps keep FOP focused on its main task: generating great PDF from XSL-FO documents c) If FOP is ever rewritten in another language for performance, these converters, being much less compute-intensive, can stay in java and keep the same interface to the FOP components that they use d) assuming I want to write a MIF converter, basing it on XSL-FO input instead of on a FOP API allows me to easily include MIF-specific constructs for applications where XSL-FO conformance is not needed but precise control of the generated MIF is (often a requirement for MIF when producing half-finished documents that are typographically reviewed before printing). In conclusion, I think an interface based on XML documents (possibly this pr.fo discussed above) is the best choice to use between the FOP property resolution stage and the structure renderers like RTF and MIF renderers. The big problem is in defining the p.res step. How far do you need to go with this? If you require all of the relative lengths resolved, e.g., you'll have to wait until the layout is done. The properties are only finalised as the area tree is being constructed. It's one of the things that makes this all so frustrating. OTOH I agree that using XML between the layout and rendering stages doesn't make sense at this stage of FOP development. Ok. Due to many other commitments, I don't have time right now (sorry, I know you're getting used to hear this) to implement this pr.fo interface, but if we agree on its usefulness I'll put this high on my list and hopefully give it a shot in the next few weeks... Peter - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, email: [EMAIL PROTECTED]
Re: Area tree - renderer (pr.fo for structure renderers)
On Monday 18 March 2002 13:37, Peter B. West wrote: . . . Bertrand Delacretaz wrote: In conclusion, I think an interface based on XML documents (possibly this pr.fo discussed above) is the best choice to use between the FOP property resolution stage and the structure renderers like RTF and MIF renderers. The big problem is in defining the p.res step. How far do you need to go with this? If you require all of the relative lengths resolved, e.g., you'll have to wait until the layout is done. The properties are only finalised as the area tree is being constructed. It's one of the things that makes this all so frustrating. ok I see. I'll try to play with this for RTF rendering based on jfor, to get a feel for how hard/useful this is. In case of jfor, what is needed is mostly property inheritance, for which AFAIK rules are well defined in FOP. I guess relative lengths will probably stay relative in the RTF code, but I'll have to play with it to be positive about this. -Bertrand - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, email: [EMAIL PROTECTED]
Re: Area tree - renderer (pr.fo for structure renderers)
Bertrand, There's another gotcha - markers. The properties in markers are resolved relative to the retrieve-marker invocation point. Peter Bertrand Delacretaz wrote: On Monday 18 March 2002 13:37, Peter B. West wrote: The big problem is in defining the p.res step. How far do you need to go with this? If you require all of the relative lengths resolved, e.g., you'll have to wait until the layout is done. The properties are only finalised as the area tree is being constructed. It's one of the things that makes this all so frustrating. ok I see. I'll try to play with this for RTF rendering based on jfor, to get a feel for how hard/useful this is. In case of jfor, what is needed is mostly property inheritance, for which AFAIK rules are well defined in FOP. I guess relative lengths will probably stay relative in the RTF code, but I'll have to play with it to be positive about this. - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, email: [EMAIL PROTECTED]
Re: Area tree - renderer (pr.fo for structure renderers)
Hi Peter, On Monday 18 March 2002 22:06, Peter B. West wrote: . . . There's another gotcha - markers. The properties in markers are resolved relative to the retrieve-marker invocation point. . . . Thanks - I'll keep this in mind when I get to play with this stuff.. -Bertrand - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, email: [EMAIL PROTECTED]
