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PDF: Update the PDF page structure comment

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Adrian Johnson 2008-01-07 21:19:35 +10:30
parent 21f842f0df
commit 25f24e79f8
1 changed files with 8 additions and 60 deletions
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68
src/cairo-pdf-surface.c
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@ -88,37 +88,6 @@
* that fallback images do not composite with any content under the
* fallback images.
*
* The group containing the supported operations (content_group_list
* in the example below) does not do any drawing directly. Instead it
* paints groups containing the drawing operations and performs
* clipping. The reason for this is that clipping operations performed
* in a group do not affect the parent group.
*
* Example PDF Page Structure:
*
* Page Content
* ------------
* /knockout_group Do
*
* knockout_group
* --------------
* /content_group_list Do
* /fallback_image_1 Do
* /fallback_image_2 Do
* ...
*
* content_group_list
* ------------------
* q
* /content_group_1 Do
* /content_group_2 Do
* 10 10 m 10 20 l 20 20 l 20 10 l h W # clip
* /content_group_3 Do
* Q q # reset clip
* /content_group_4 Do
* Q
*
*
* Streams:
*
* This PDF surface has three types of streams:
@ -139,42 +108,21 @@
*
* Content Stream:
* The Content Stream is opened and closed with the following functions:
* _cairo_pdf_surface_start_content_stream ()
* _cairo_pdf_surface_stop_content_stream ()
* _cairo_pdf_surface_open_content_stream ()
* _cairo_pdf_surface_close_content_stream ()
*
* The Content Stream is written to content_group_n groups (as shown
* in the page structure example). The Content Stream may be paused
* and resumed with the following functions:
* _cairo_pdf_surface_pause_content_stream ()
* _cairo_pdf_surface_resume_content_stream ()
*
* When the Content Stream is paused, a PDF Stream or Group Stream
* may be opened. After closing the PDF Stream or Group Stream the
* Content Stream may be resumed.
*
* The Content Stream contains the text and graphics operators. When
* a pattern is required the Content Stream is paused, a PDF Stream
* is opened, the pattern is written to a PDF Stream, the PDF Stream
* is closed, then the Content Stream is resumed.
*
* Each group comprising the Content Stream is stored in memory
* until the stream is closed or the maximum group size is
* exceeded. This is due to the need to list all resources used in
* the group in the group's stream dictionary.
* The Content Stream contains the text and graphics operators.
*
* Group Stream:
* A Group Stream may be opened and closed with the following functions:
* _cairo_pdf_surface_open_group ()
* _cairo_pdf_surface_close_group ()
*
* A Group Stream is written to a separate group in the PDF file
* that is not part of the Content Stream. Group Streams are also
* stored in memory until the stream is closed due to the need to
* list the resources used in the group in the group's stream
* dictionary.
*
* Group Streams are used for short sequences of graphics operations
* that need to be in a separate group from the Content Stream.
* A Group Stream is a Form XObject. It is used for short sequences
* of operators. As the content is very short the group is stored in
* memory until it is closed. This allows some optimization such as
* including the Resource dictionary and stream length inside the
* XObject instead of using an indirect object.
*/
typedef struct _cairo_pdf_object {