libjava/gnu/awt/j2d/MappedRaster.java

   1 /* Copyright (C) 2000  Free Software Foundation
   2
   3    This file is part of libgcj.
   4
   5 This software is copyrighted work licensed under the terms of the
   6 Libgcj License.  Please consult the file "LIBGCJ_LICENSE" for
   7 details.  */
   8
   9 package gnu.awt.j2d;
  10
  11 import java.awt.image.WritableRaster;
  12 import java.awt.image.ColorModel;
  13
  14 /* The raster and associated properties of a mapped screen region.
  15  * The compositing capabilities of backends are often insufficient.
  16  * The backend may not support alpha blending, or may not support some
  17  * other special compositing rule.  This means that compositing must
  18  * sometimes be done within the rendering pipeline.  The general
  19  * compositing operation consists of combining new color and alpha
  20  * values with existing color values on the drawing surface, to find
  21  * the new color values for the drawing surface. The way the values
  22  * are combined, determines what kind of compositing operation that is
  23  * performed.  The default compositing operation is alpha compositing.
  24  *
  25  * <p>In order to perform alpha compositing and other compositing
  26  * operations, we need access to the color values of the imagery that
  27  * has already been drawn on the drawing surface.  The
  28  * DirectRasterGraphics interface must therefore contain methods that
  29  * makes it possible to gain access to the pixel values of the drawing
  30  * surface.  The methods are modeled after the POSIX mmap() and
  31  * munmap() functions.  But, instead of mapping and unmapping portions
  32  * of data from a file descriptor to memory, the methods in
  33  * DirectRasterGraphics maps and unmaps portions of the drawing
  34  * surface to data arrays within writable raster objects.  A call to
  35  * mapRaster() will return a writable raster object, encapsulating the
  36  * image data of the drawing surface in the requested domain. The data
  37  * encapsulated by this raster object can be modified using the
  38  * WritableRaster API, or the data buffers can be retrieved from the
  39  * raster, so that the data arrays can be manipulated directly.  When
  40  * the raster image has been modified as desired, the data can be
  41  * resynchronized with the drawing surface by calling mapRaster().
  42  *
  43  * <p>As with mmap() and munmap() the methods may work by direct
  44  * manipulation of shared memory, (i.e. the raster object directly
  45  * wraps the actual image data of the drawing surface), or may make a
  46  * private copy that is resynched when the raster is unmapped. The
  47  * backend may choose to implement either mechanism, and the pipeline
  48  * code should not care what mechanism is actually used.  This design
  49  * allows us to make full use of speedups such as X shared memory
  50  * extentions when available.
  51  */
  52 public class MappedRaster
  53 {
  54   WritableRaster raster;
  55   ColorModel cm;
  56
  57   public MappedRaster(WritableRaster raster, ColorModel cm)
  58   {
  59     this.raster = raster;
  60     this.cm = cm;
  61   }
  62
  63   public final WritableRaster getRaster()
  64   {
  65     return raster;
  66   }
  67
  68   public final ColorModel getColorModel()
  69   {
  70     return cm;
  71   }
  72 }