src/java.desktop/share/classes/java/awt/Composite.java

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package java.awt;

import java.awt.image.ColorModel;

/**
 * The {@code Composite} interface, along with
 * {@link CompositeContext}, defines the methods to compose a draw
 * primitive with the underlying graphics area.
 * After the {@code Composite} is set in the
 * {@link Graphics2D} context, it combines a shape, text, or an image
 * being rendered with the colors that have already been rendered
 * according to pre-defined rules. The classes
 * implementing this interface provide the rules and a method to create
 * the context for a particular operation.
 * {@code CompositeContext} is an environment used by the
 * compositing operation, which is created by the {@code Graphics2D}
 * prior to the start of the operation.  {@code CompositeContext}
 * contains private information and resources needed for a compositing
 * operation.  When the {@code CompositeContext} is no longer needed,
 * the {@code Graphics2D} object disposes of it in order to reclaim
 * resources allocated for the operation.
 * <p>
 * Instances of classes implementing {@code Composite} must be
 * immutable because the {@code Graphics2D} does not clone
 * these objects when they are set as an attribute with the
 * {@code setComposite} method or when the {@code Graphics2D}
 * object is cloned.  This is to avoid undefined rendering behavior of
 * {@code Graphics2D}, resulting from the modification of
 * the {@code Composite} object after it has been set in the
 * {@code Graphics2D} context.
 * @see AlphaComposite
 * @see CompositeContext
 * @see Graphics2D#setComposite
 */
public interface Composite {

    /**
     * Creates a context containing state that is used to perform
     * the compositing operation.  In a multi-threaded environment,
     * several contexts can exist simultaneously for a single
     * {@code Composite} object.
     * @param srcColorModel  the {@link ColorModel} of the source
     * @param dstColorModel  the {@code ColorModel} of the destination
     * @param hints the hint that the context object uses to choose between
     * rendering alternatives
     * @return the {@code CompositeContext} object used to perform the
     * compositing operation.
     */
    public CompositeContext createContext(ColorModel srcColorModel,
                                          ColorModel dstColorModel,
                                          RenderingHints hints);

}