awt/font/FontRenderContext.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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/*
 * @author Charlton Innovations, Inc.
 */

package java.awt.font;

import java.awt.RenderingHints;
import static java.awt.RenderingHints.*;
import java.awt.geom.AffineTransform;

/**
*   The {@code FontRenderContext} class is a container for the
*   information needed to correctly measure text.  The measurement of text
*   can vary because of rules that map outlines to pixels, and rendering
*   hints provided by an application.
*   <p>
*   One such piece of information is a transform that scales
*   typographical points to pixels. (A point is defined to be exactly 1/72
*   of an inch, which is slightly different than
*   the traditional mechanical measurement of a point.)  A character that
*   is rendered at 12pt on a 600dpi device might have a different size
*   than the same character rendered at 12pt on a 72dpi device because of
*   such factors as rounding to pixel boundaries and hints that the font
*   designer may have specified.
*   <p>
*   Anti-aliasing and Fractional-metrics specified by an application can also
*   affect the size of a character because of rounding to pixel
*   boundaries.
*   <p>
*   Typically, instances of {@code FontRenderContext} are
*   obtained from a {@link java.awt.Graphics2D Graphics2D} object.  A
*   {@code FontRenderContext} which is directly constructed will
*   most likely not represent any actual graphics device, and may lead
*   to unexpected or incorrect results.
*   @see java.awt.RenderingHints#KEY_TEXT_ANTIALIASING
*   @see java.awt.RenderingHints#KEY_FRACTIONALMETRICS
*   @see java.awt.Graphics2D#getFontRenderContext()
*   @see java.awt.font.LineMetrics
*/

public class FontRenderContext {
    private transient AffineTransform tx;
    private transient Object aaHintValue;
    private transient Object fmHintValue;
    private transient boolean defaulting;

    /**
     * Constructs a new {@code FontRenderContext}
     * object.
     *
     */
    protected FontRenderContext() {
        aaHintValue = VALUE_TEXT_ANTIALIAS_DEFAULT;
        fmHintValue = VALUE_FRACTIONALMETRICS_DEFAULT;
        defaulting = true;
    }

    /**
     * Constructs a {@code FontRenderContext} object from an
     * optional {@link AffineTransform} and two {@code boolean}
     * values that determine if the newly constructed object has
     * anti-aliasing or fractional metrics.
     * In each case the boolean values {@code true} and {@code false}
     * correspond to the rendering hint values {@code ON} and
     * {@code OFF} respectively.
     * <p>
     * To specify other hint values, use the constructor which
     * specifies the rendering hint values as parameters :
     * {@link #FontRenderContext(AffineTransform, Object, Object)}.
     * @param tx the transform which is used to scale typographical points
     * to pixels in this {@code FontRenderContext}.  If null, an
     * identity transform is used.
     * @param isAntiAliased determines if the newly constructed object
     * has anti-aliasing.
     * @param usesFractionalMetrics determines if the newly constructed
     * object has fractional metrics.
     */
    public FontRenderContext(AffineTransform tx,
                            boolean isAntiAliased,
                            boolean usesFractionalMetrics) {
        if (tx != null && !tx.isIdentity()) {
            this.tx = new AffineTransform(tx);
        }
        if (isAntiAliased) {
            aaHintValue = VALUE_TEXT_ANTIALIAS_ON;
        } else {
            aaHintValue = VALUE_TEXT_ANTIALIAS_OFF;
        }
        if (usesFractionalMetrics) {
            fmHintValue = VALUE_FRACTIONALMETRICS_ON;
        } else {
            fmHintValue = VALUE_FRACTIONALMETRICS_OFF;
        }
    }

    /**
     * Constructs a {@code FontRenderContext} object from an
     * optional {@link AffineTransform} and two {@code Object}
     * values that determine if the newly constructed object has
     * anti-aliasing or fractional metrics.
     * @param tx the transform which is used to scale typographical points
     * to pixels in this {@code FontRenderContext}.  If null, an
     * identity transform is used.
     * @param aaHint - one of the text antialiasing rendering hint values
     * defined in {@link java.awt.RenderingHints java.awt.RenderingHints}.
     * Any other value will throw {@code IllegalArgumentException}.
     * {@link java.awt.RenderingHints#VALUE_TEXT_ANTIALIAS_DEFAULT VALUE_TEXT_ANTIALIAS_DEFAULT}
     * may be specified, in which case the mode used is implementation
     * dependent.
     * @param fmHint - one of the text fractional rendering hint values defined
     * in {@link java.awt.RenderingHints java.awt.RenderingHints}.
     * {@link java.awt.RenderingHints#VALUE_FRACTIONALMETRICS_DEFAULT VALUE_FRACTIONALMETRICS_DEFAULT}
     * may be specified, in which case the mode used is implementation
     * dependent.
     * Any other value will throw {@code IllegalArgumentException}
     * @throws IllegalArgumentException if the hints are not one of the
     * legal values.
     * @since 1.6
     */
    public FontRenderContext(AffineTransform tx, Object aaHint, Object fmHint){
        if (tx != null && !tx.isIdentity()) {
            this.tx = new AffineTransform(tx);
        }
        try {
            if (KEY_TEXT_ANTIALIASING.isCompatibleValue(aaHint)) {
                aaHintValue = aaHint;
            } else {
                throw new IllegalArgumentException("AA hint:" + aaHint);
            }
        } catch (Exception e) {
            throw new IllegalArgumentException("AA hint:" +aaHint);
        }
        try {
            if (KEY_FRACTIONALMETRICS.isCompatibleValue(fmHint)) {
                fmHintValue = fmHint;
            } else {
                throw new IllegalArgumentException("FM hint:" + fmHint);
            }
        } catch (Exception e) {
            throw new IllegalArgumentException("FM hint:" +fmHint);
        }
    }

    /**
     * Indicates whether or not this {@code FontRenderContext} object
     * measures text in a transformed render context.
     * @return  {@code true} if this {@code FontRenderContext}
     *          object has a non-identity AffineTransform attribute.
     *          {@code false} otherwise.
     * @see     java.awt.font.FontRenderContext#getTransform
     * @since   1.6
     */
    public boolean isTransformed() {
        if (!defaulting) {
            return tx != null;
        } else {
            return !getTransform().isIdentity();
        }
    }

    /**
     * Returns the integer type of the affine transform for this
     * {@code FontRenderContext} as specified by
     * {@link java.awt.geom.AffineTransform#getType()}
     * @return the type of the transform.
     * @see AffineTransform
     * @since 1.6
     */
    public int getTransformType() {
        if (!defaulting) {
            if (tx == null) {
                return AffineTransform.TYPE_IDENTITY;
            } else {
                return tx.getType();
            }
        } else {
            return getTransform().getType();
        }
    }

    /**
    *   Gets the transform that is used to scale typographical points
    *   to pixels in this {@code FontRenderContext}.
    *   @return the {@code AffineTransform} of this
    *    {@code FontRenderContext}.
    *   @see AffineTransform
    */
    public AffineTransform getTransform() {
        return (tx == null) ? new AffineTransform() : new AffineTransform(tx);
    }

    /**
    * Returns a boolean which indicates whether or not some form of
    * antialiasing is specified by this {@code FontRenderContext}.
    * Call {@link #getAntiAliasingHint() getAntiAliasingHint()}
    * for the specific rendering hint value.
    *   @return    {@code true}, if text is anti-aliased in this
    *   {@code FontRenderContext}; {@code false} otherwise.
    *   @see        java.awt.RenderingHints#KEY_TEXT_ANTIALIASING
    *   @see #FontRenderContext(AffineTransform,boolean,boolean)
    *   @see #FontRenderContext(AffineTransform,Object,Object)
    */
    public boolean isAntiAliased() {
        return !(aaHintValue == VALUE_TEXT_ANTIALIAS_OFF ||
                 aaHintValue == VALUE_TEXT_ANTIALIAS_DEFAULT);
    }

    /**
    * Returns a boolean which whether text fractional metrics mode
    * is used in this {@code FontRenderContext}.
    * Call {@link #getFractionalMetricsHint() getFractionalMetricsHint()}
    * to obtain the corresponding rendering hint value.
    *   @return    {@code true}, if layout should be performed with
    *   fractional metrics; {@code false} otherwise.
    *               in this {@code FontRenderContext}.
    *   @see java.awt.RenderingHints#KEY_FRACTIONALMETRICS
    *   @see #FontRenderContext(AffineTransform,boolean,boolean)
    *   @see #FontRenderContext(AffineTransform,Object,Object)
    */
    public boolean usesFractionalMetrics() {
        return !(fmHintValue == VALUE_FRACTIONALMETRICS_OFF ||
                 fmHintValue == VALUE_FRACTIONALMETRICS_DEFAULT);
    }

    /**
     * Return the text anti-aliasing rendering mode hint used in this
     * {@code FontRenderContext}.
     * This will be one of the text antialiasing rendering hint values
     * defined in {@link java.awt.RenderingHints java.awt.RenderingHints}.
     * @return  text anti-aliasing rendering mode hint used in this
     * {@code FontRenderContext}.
     * @since 1.6
     */
    public Object getAntiAliasingHint() {
        if (defaulting) {
            if (isAntiAliased()) {
                 return VALUE_TEXT_ANTIALIAS_ON;
            } else {
                return VALUE_TEXT_ANTIALIAS_OFF;
            }
        }
        return aaHintValue;
    }

    /**
     * Return the text fractional metrics rendering mode hint used in this
     * {@code FontRenderContext}.
     * This will be one of the text fractional metrics rendering hint values
     * defined in {@link java.awt.RenderingHints java.awt.RenderingHints}.
     * @return the text fractional metrics rendering mode hint used in this
     * {@code FontRenderContext}.
     * @since 1.6
     */
    public Object getFractionalMetricsHint() {
        if (defaulting) {
            if (usesFractionalMetrics()) {
                 return VALUE_FRACTIONALMETRICS_ON;
            } else {
                return VALUE_FRACTIONALMETRICS_OFF;
            }
        }
        return fmHintValue;
    }

    /**
     * Return true if obj is an instance of FontRenderContext and has the same
     * transform, antialiasing, and fractional metrics values as this.
     * @param obj the object to test for equality
     * @return {@code true} if the specified object is equal to
     *         this {@code FontRenderContext}; {@code false}
     *         otherwise.
     */
    public boolean equals(Object obj) {
        try {
            return equals((FontRenderContext)obj);
        }
        catch (ClassCastException e) {
            return false;
        }
    }

    /**
     * Return true if rhs has the same transform, antialiasing,
     * and fractional metrics values as this.
     * @param rhs the {@code FontRenderContext} to test for equality
     * @return {@code true} if {@code rhs} is equal to
     *         this {@code FontRenderContext}; {@code false}
     *         otherwise.
     * @since 1.4
     */
    public boolean equals(FontRenderContext rhs) {
        if (this == rhs) {
            return true;
        }
        if (rhs == null) {
            return false;
        }

        /* if neither instance is a subclass, reference values directly. */
        if (!rhs.defaulting && !defaulting) {
            if (rhs.aaHintValue == aaHintValue &&
                rhs.fmHintValue == fmHintValue) {

                return tx == null ? rhs.tx == null : tx.equals(rhs.tx);
            }
            return false;
        } else {
            return
                rhs.getAntiAliasingHint() == getAntiAliasingHint() &&
                rhs.getFractionalMetricsHint() == getFractionalMetricsHint() &&
                rhs.getTransform().equals(getTransform());
        }
    }

    /**
     * Return a hashcode for this FontRenderContext.
     */
    public int hashCode() {
        int hash = tx == null ? 0 : tx.hashCode();
        /* SunHints value objects have identity hashcode, so we can rely on
         * this to ensure that two equal FRC's have the same hashcode.
         */
        if (defaulting) {
            hash += getAntiAliasingHint().hashCode();
            hash += getFractionalMetricsHint().hashCode();
        } else {
            hash += aaHintValue.hashCode();
            hash += fmHintValue.hashCode();
        }
        return hash;
    }
}