harvey/sys/src/cmd/gs/src/gscompt.h

/* Copyright (C) 1997 Aladdin Enterprises.  All rights reserved.
  
  This file is part of AFPL Ghostscript.
  
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  she says so in writing.  Refer to the Aladdin Free Public License (the
  "License") for full details.
  
  Every copy of AFPL Ghostscript must include a copy of the License, normally
  in a plain ASCII text file named PUBLIC.  The License grants you the right
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  requires that the copyright notice and this notice be preserved on all
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*/

/*$Id: gscompt.h,v 1.2 2000/09/19 19:00:26 lpd Exp $ */
/* Abstract types for compositing objects */

#ifndef gscompt_INCLUDED
#  define gscompt_INCLUDED

/*
 * Compositing is the next-to-last step in the rendering pipeline.
 * It occurs after color correction but before halftoning (if needed).
 *
 * gs_composite_t is the abstract superclass for compositing functions such
 * as RasterOp functions or alpha-based compositing.  Concrete subclasses
 * must provide a default implementation (presumably based on
 * get_bits_rectangle and copy_color) for devices that provide no optimized
 * implementation of their own.
 *
 * A client that wants to produce composited output asks the target device
 * to create an appropriate compositing device based on the target device
 * and the gs_composite_t (and possibly other elements of the imager state).
 * If the target device doesn't have its own implementation for the
 * requested function, format, and state, it passes the buck to the
 * gs_composite_t, which may make further tests for special cases before
 * creating and returning a compositing device that uses the default
 * implementation.
 */
typedef struct gs_composite_s gs_composite_t;

/*
 * To enable fast cache lookup and equality testing, compositing functions,
 * like halftones, black generation functions, etc., carry a unique ID (time
 * stamp).
 */
gs_id gs_composite_id(P1(const gs_composite_t * pcte));

#endif /* gscompt_INCLUDED */