org.eclipse.swt.graphics.FontMetrics.java Source code

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/*******************************************************************************
 * Copyright (c) 2000, 2018 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.swt.graphics;

import org.eclipse.swt.internal.*;
import org.eclipse.swt.internal.win32.*;

/**
 * Instances of this class provide measurement information
 * about fonts including ascent, descent, height, leading
 * space between rows, and average character width.
 * <code>FontMetrics</code> are obtained from <code>GC</code>s
 * using the <code>getFontMetrics()</code> method.
 *
 * @see GC#getFontMetrics
 * @see <a href="http://www.eclipse.org/swt/">Sample code and further information</a>
 */
public final class FontMetrics {

    /**
     * On Windows, handle is a Win32 TEXTMETRIC struct
     * (Warning: This field is platform dependent)
     * <p>
     * <b>IMPORTANT:</b> This field is <em>not</em> part of the SWT
     * public API. It is marked public only so that it can be shared
     * within the packages provided by SWT. It is not available on all
     * platforms and should never be accessed from application code.
     * </p>
     *
     * @noreference This field is not intended to be referenced by clients.
     */
    public TEXTMETRIC handle;

    /**
     * Prevents instances from being created outside the package.
     */
    FontMetrics() {
    }

    /**
     * Compares the argument to the receiver, and returns true
     * if they represent the <em>same</em> object using a class
     * specific comparison.
     *
     * @param object the object to compare with this object
     * @return <code>true</code> if the object is the same as this object and <code>false</code> otherwise
     *
     * @see #hashCode
     */
    @Override
    public boolean equals(Object object) {
        if (object == this)
            return true;
        if (!(object instanceof FontMetrics))
            return false;
        TEXTMETRIC metric = ((FontMetrics) object).handle;
        return handle.tmHeight == metric.tmHeight && handle.tmAscent == metric.tmAscent
                && handle.tmDescent == metric.tmDescent && handle.tmInternalLeading == metric.tmInternalLeading
                && handle.tmExternalLeading == metric.tmExternalLeading
                && handle.tmAveCharWidth == metric.tmAveCharWidth && handle.tmMaxCharWidth == metric.tmMaxCharWidth
                && handle.tmWeight == metric.tmWeight && handle.tmOverhang == metric.tmOverhang
                && handle.tmDigitizedAspectX == metric.tmDigitizedAspectX
                && handle.tmDigitizedAspectY == metric.tmDigitizedAspectY &&
                //      handle.tmFirstChar == metric.tmFirstChar &&
                //      handle.tmLastChar == metric.tmLastChar &&
                //      handle.tmDefaultChar == metric.tmDefaultChar &&
                //      handle.tmBreakChar == metric.tmBreakChar &&
                handle.tmItalic == metric.tmItalic && handle.tmUnderlined == metric.tmUnderlined
                && handle.tmStruckOut == metric.tmStruckOut && handle.tmPitchAndFamily == metric.tmPitchAndFamily
                && handle.tmCharSet == metric.tmCharSet;
    }

    /**
     * Returns the ascent of the font described by the receiver. A
     * font's <em>ascent</em> is the distance from the baseline to the
     * top of actual characters, not including any of the leading area,
     * measured in points.
     *
     * @return the ascent of the font
     */
    public int getAscent() {
        return DPIUtil.autoScaleDown(handle.tmAscent - handle.tmInternalLeading);
    }

    /**
     * Returns the average character width, measured in points,
     * of the font described by the receiver.
     *
     * @return the average character width of the font
     * @since 3.107
     */
    public double getAverageCharacterWidth() {
        return getAverageCharWidth();
    }

    /**
     * Returns the average character width, measured in points,
     * of the font described by the receiver.
     *
     * @return the average character width of the font
     * @deprecated Use getAverageCharacterWidth() instead
     */
    public int getAverageCharWidth() {
        return DPIUtil.autoScaleDown(handle.tmAveCharWidth);
    }

    /**
     * Returns the descent of the font described by the receiver. A
     * font's <em>descent</em> is the distance from the baseline to the
     * bottom of actual characters, not including any of the leading area,
     * measured in points.
     *
     * @return the descent of the font
     */
    public int getDescent() {
        return DPIUtil.autoScaleDown(handle.tmDescent);
    }

    /**
     * Returns the height of the font described by the receiver,
     * measured in points. A font's <em>height</em> is the sum of
     * its ascent, descent and leading area.
     *
     * @return the height of the font
     *
     * @see #getAscent
     * @see #getDescent
     * @see #getLeading
     */
    public int getHeight() {
        return DPIUtil.autoScaleDown(handle.tmHeight);
    }

    /**
     * Returns the leading area of the font described by the
     * receiver. A font's <em>leading area</em> is the space
     * above its ascent which may include accents or other marks.
     *
     * @return the leading space of the font
     */
    public int getLeading() {
        /*
         * HiHPI rounding problem (bug 490743 comment 17):
         *
         * API clients expect this invariant:
         *    getHeight() == getLeading() + getAscent() + getDescent()
         *
         * Separate rounding of each RHS term can break the invariant.
         *
         * An additional problem is that ascent and descent are more important to
         * be as close as possible to the real value. Any necessary rounding
         * adjustment should go into leading, that's why compute this as a derived
         * value here:
         */
        return getHeight() - getAscent() - getDescent();
    }

    /**
     * Returns an integer hash code for the receiver. Any two
     * objects that return <code>true</code> when passed to
     * <code>equals</code> must return the same value for this
     * method.
     *
     * @return the receiver's hash
     *
     * @see #equals
     */
    @Override
    public int hashCode() {
        return handle.tmHeight ^ handle.tmAscent ^ handle.tmDescent ^ handle.tmInternalLeading
                ^ handle.tmExternalLeading ^ handle.tmAveCharWidth ^ handle.tmMaxCharWidth ^ handle.tmWeight
                ^ handle.tmOverhang ^ handle.tmDigitizedAspectX ^ handle.tmDigitizedAspectY ^
                //      handle.tmFirstChar ^ handle.tmLastChar ^ handle.tmDefaultChar ^ handle.tmBreakChar ^
                handle.tmItalic ^ handle.tmUnderlined ^ handle.tmStruckOut ^ handle.tmPitchAndFamily
                ^ handle.tmCharSet;
    }

    /**
     * Invokes platform specific functionality to allocate a new font metrics.
     * <p>
     * <b>IMPORTANT:</b> This method is <em>not</em> part of the public
     * API for <code>FontMetrics</code>. It is marked public only so that
     * it can be shared within the packages provided by SWT. It is not
     * available on all platforms, and should never be called from
     * application code.
     * </p>
     *
     * @param handle the <code>TEXTMETRIC</code> containing information about a font
     * @return a new font metrics object containing the specified <code>TEXTMETRIC</code>
     *
     * @noreference This method is not intended to be referenced by clients.
     */
    public static FontMetrics win32_new(TEXTMETRIC handle) {
        FontMetrics fontMetrics = new FontMetrics();
        fontMetrics.handle = handle;
        return fontMetrics;
    }

}