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Java example source code file (FontMetrics.java)
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The FontMetrics.java Java example source code
/*
* Copyright (c) 1995, 2013, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* 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.
*
* 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
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.awt;
import java.awt.Graphics2D;
import java.awt.font.FontRenderContext;
import java.awt.font.LineMetrics;
import java.awt.geom.Rectangle2D;
import java.text.CharacterIterator;
/**
* The <code>FontMetrics class defines a font metrics object, which
* encapsulates information about the rendering of a particular font on a
* particular screen.
* <p>
* <b>Note to subclassers: Since many of these methods form closed,
* mutually recursive loops, you must take care that you implement
* at least one of the methods in each such loop to prevent
* infinite recursion when your subclass is used.
* In particular, the following is the minimal suggested set of methods
* to override in order to ensure correctness and prevent infinite
* recursion (though other subsets are equally feasible):
* <ul>
* <li>{@link #getAscent()}
* <li>{@link #getLeading()}
* <li>{@link #getMaxAdvance()}
* <li>{@link #charWidth(char)}
* <li>{@link #charsWidth(char[], int, int)}
* </ul>
* <p>
* <img src="doc-files/FontMetrics-1.gif" alt="The letter 'p' showing its 'reference point'"
* style="border:15px; float:right; margin: 7px 10px;">
* Note that the implementations of these methods are
* inefficient, so they are usually overridden with more efficient
* toolkit-specific implementations.
* <p>
* When an application asks to place a character at the position
* (<i>x, y), the character is placed so that its
* reference point (shown as the dot in the accompanying image) is
* put at that position. The reference point specifies a horizontal
* line called the <i>baseline of the character. In normal
* printing, the baselines of characters should align.
* <p>
* In addition, every character in a font has an <i>ascent, a
* <i>descent, and an advance width. The ascent is the
* amount by which the character ascends above the baseline. The
* descent is the amount by which the character descends below the
* baseline. The advance width indicates the position at which AWT
* should place the next character.
* <p>
* An array of characters or a string can also have an ascent, a
* descent, and an advance width. The ascent of the array is the
* maximum ascent of any character in the array. The descent is the
* maximum descent of any character in the array. The advance width
* is the sum of the advance widths of each of the characters in the
* character array. The advance of a <code>String is the
* distance along the baseline of the <code>String. This
* distance is the width that should be used for centering or
* right-aligning the <code>String.
* <p>Note that the advance of a String is not necessarily
* the sum of the advances of its characters measured in isolation
* because the width of a character can vary depending on its context.
* For example, in Arabic text, the shape of a character can change
* in order to connect to other characters. Also, in some scripts,
* certain character sequences can be represented by a single shape,
* called a <em>ligature. Measuring characters individually does
* not account for these transformations.
* <p>Font metrics are baseline-relative, meaning that they are
* generally independent of the rotation applied to the font (modulo
* possible grid hinting effects). See {@link java.awt.Font Font}.
*
* @author Jim Graham
* @see java.awt.Font
* @since JDK1.0
*/
public abstract class FontMetrics implements java.io.Serializable {
static {
/* ensure that the necessary native libraries are loaded */
Toolkit.loadLibraries();
if (!GraphicsEnvironment.isHeadless()) {
initIDs();
}
}
private static final FontRenderContext
DEFAULT_FRC = new FontRenderContext(null, false, false);
/**
* The actual {@link Font} from which the font metrics are
* created.
* This cannot be null.
*
* @serial
* @see #getFont()
*/
protected Font font;
/*
* JDK 1.1 serialVersionUID
*/
private static final long serialVersionUID = 1681126225205050147L;
/**
* Creates a new <code>FontMetrics object for finding out
* height and width information about the specified <code>Font
* and specific character glyphs in that <code>Font.
* @param font the <code>Font
* @see java.awt.Font
*/
protected FontMetrics(Font font) {
this.font = font;
}
/**
* Gets the <code>Font described by this
* <code>FontMetrics object.
* @return the <code>Font described by this
* <code>FontMetrics object.
*/
public Font getFont() {
return font;
}
/**
* Gets the <code>FontRenderContext used by this
* <code>FontMetrics object to measure text.
* <p>
* Note that methods in this class which take a <code>Graphics
* parameter measure text using the <code>FontRenderContext
* of that <code>Graphics object, and not this
* <code>FontRenderContext
* @return the <code>FontRenderContext used by this
* <code>FontMetrics object.
* @since 1.6
*/
public FontRenderContext getFontRenderContext() {
return DEFAULT_FRC;
}
/**
* Determines the <em>standard leading of the
* <code>Font described by this FontMetrics
* object. The standard leading, or
* interline spacing, is the logical amount of space to be reserved
* between the descent of one line of text and the ascent of the next
* line. The height metric is calculated to include this extra space.
* @return the standard leading of the <code>Font.
* @see #getHeight()
* @see #getAscent()
* @see #getDescent()
*/
public int getLeading() {
return 0;
}
/**
* Determines the <em>font ascent of the Font
* described by this <code>FontMetrics object. The font ascent
* is the distance from the font's baseline to the top of most
* alphanumeric characters. Some characters in the <code>Font
* might extend above the font ascent line.
* @return the font ascent of the <code>Font.
* @see #getMaxAscent()
*/
public int getAscent() {
return font.getSize();
}
/**
* Determines the <em>font descent of the Font
* described by this
* <code>FontMetrics object. The font descent is the distance
* from the font's baseline to the bottom of most alphanumeric
* characters with descenders. Some characters in the
* <code>Font might extend
* below the font descent line.
* @return the font descent of the <code>Font.
* @see #getMaxDescent()
*/
public int getDescent() {
return 0;
}
/**
* Gets the standard height of a line of text in this font. This
* is the distance between the baseline of adjacent lines of text.
* It is the sum of the leading + ascent + descent. Due to rounding
* this may not be the same as getAscent() + getDescent() + getLeading().
* There is no guarantee that lines of text spaced at this distance are
* disjoint; such lines may overlap if some characters overshoot
* either the standard ascent or the standard descent metric.
* @return the standard height of the font.
* @see #getLeading()
* @see #getAscent()
* @see #getDescent()
*/
public int getHeight() {
return getLeading() + getAscent() + getDescent();
}
/**
* Determines the maximum ascent of the <code>Font
* described by this <code>FontMetrics object. No character
* extends further above the font's baseline than this height.
* @return the maximum ascent of any character in the
* <code>Font.
* @see #getAscent()
*/
public int getMaxAscent() {
return getAscent();
}
/**
* Determines the maximum descent of the <code>Font
* described by this <code>FontMetrics object. No character
* extends further below the font's baseline than this height.
* @return the maximum descent of any character in the
* <code>Font.
* @see #getDescent()
*/
public int getMaxDescent() {
return getDescent();
}
/**
* For backward compatibility only.
* @return the maximum descent of any character in the
* <code>Font.
* @see #getMaxDescent()
* @deprecated As of JDK version 1.1.1,
* replaced by <code>getMaxDescent().
*/
@Deprecated
public int getMaxDecent() {
return getMaxDescent();
}
/**
* Gets the maximum advance width of any character in this
* <code>Font. The advance is the
* distance from the leftmost point to the rightmost point on the
* string's baseline. The advance of a <code>String is
* not necessarily the sum of the advances of its characters.
* @return the maximum advance width of any character
* in the <code>Font, or -1 if the
* maximum advance width is not known.
*/
public int getMaxAdvance() {
return -1;
}
/**
* Returns the advance width of the specified character in this
* <code>Font. The advance is the
* distance from the leftmost point to the rightmost point on the
* character's baseline. Note that the advance of a
* <code>String is not necessarily the sum of the advances
* of its characters.
*
* <p>This method doesn't validate the specified character to be a
* valid Unicode code point. The caller must validate the
* character value using {@link
* java.lang.Character#isValidCodePoint(int)
* Character.isValidCodePoint} if necessary.
*
* @param codePoint the character (Unicode code point) to be measured
* @return the advance width of the specified character
* in the <code>Font described by this
* <code>FontMetrics object.
* @see #charsWidth(char[], int, int)
* @see #stringWidth(String)
*/
public int charWidth(int codePoint) {
if (!Character.isValidCodePoint(codePoint)) {
codePoint = 0xffff; // substitute missing glyph width
}
if (codePoint < 256) {
return getWidths()[codePoint];
} else {
char[] buffer = new char[2];
int len = Character.toChars(codePoint, buffer, 0);
return charsWidth(buffer, 0, len);
}
}
/**
* Returns the advance width of the specified character in this
* <code>Font. The advance is the
* distance from the leftmost point to the rightmost point on the
* character's baseline. Note that the advance of a
* <code>String is not necessarily the sum of the advances
* of its characters.
*
* <p>Note: This method cannot handle described by this
* <code>FontMetrics object.
* @see #charsWidth(char[], int, int)
* @see #stringWidth(String)
*/
public int charWidth(char ch) {
if (ch < 256) {
return getWidths()[ch];
}
char data[] = {ch};
return charsWidth(data, 0, 1);
}
/**
* Returns the total advance width for showing the specified
* <code>String in this Font. The advance
* is the distance from the leftmost point to the rightmost point
* on the string's baseline.
* <p>
* Note that the advance of a <code>String is
* not necessarily the sum of the advances of its characters.
* @param str the <code>String to be measured
* @return the advance width of the specified <code>String
* in the <code>Font described by this
* <code>FontMetrics.
* @throws NullPointerException if str is null.
* @see #bytesWidth(byte[], int, int)
* @see #charsWidth(char[], int, int)
* @see #getStringBounds(String, Graphics)
*/
public int stringWidth(String str) {
int len = str.length();
char data[] = new char[len];
str.getChars(0, len, data, 0);
return charsWidth(data, 0, len);
}
/**
* Returns the total advance width for showing the specified array
* of characters in this <code>Font. The advance is the
* distance from the leftmost point to the rightmost point on the
* string's baseline. The advance of a <code>String
* is not necessarily the sum of the advances of its characters.
* This is equivalent to measuring a <code>String of the
* characters in the specified range.
* @param data the array of characters to be measured
* @param off the start offset of the characters in the array
* @param len the number of characters to be measured from the array
* @return the advance width of the subarray of the specified
* <code>char array in the font described by
* this <code>FontMetrics object.
* @throws NullPointerException if <code>data is null.
* @throws IndexOutOfBoundsException if the <code>off
* and <code>len arguments index characters outside
* the bounds of the <code>data array.
* @see #charWidth(int)
* @see #charWidth(char)
* @see #bytesWidth(byte[], int, int)
* @see #stringWidth(String)
*/
public int charsWidth(char data[], int off, int len) {
return stringWidth(new String(data, off, len));
}
/**
* Returns the total advance width for showing the specified array
* of bytes in this <code>Font. The advance is the
* distance from the leftmost point to the rightmost point on the
* string's baseline. The advance of a <code>String
* is not necessarily the sum of the advances of its characters.
* This is equivalent to measuring a <code>String of the
* characters in the specified range.
* @param data the array of bytes to be measured
* @param off the start offset of the bytes in the array
* @param len the number of bytes to be measured from the array
* @return the advance width of the subarray of the specified
* <code>byte array in the Font
* described by
* this <code>FontMetrics object.
* @throws NullPointerException if <code>data is null.
* @throws IndexOutOfBoundsException if the <code>off
* and <code>len arguments index bytes outside
* the bounds of the <code>data array.
* @see #charsWidth(char[], int, int)
* @see #stringWidth(String)
*/
public int bytesWidth(byte data[], int off, int len) {
return stringWidth(new String(data, 0, off, len));
}
/**
* Gets the advance widths of the first 256 characters in the
* <code>Font. The advance is the
* distance from the leftmost point to the rightmost point on the
* character's baseline. Note that the advance of a
* <code>String is not necessarily the sum of the advances
* of its characters.
* @return an array storing the advance widths of the
* characters in the <code>Font
* described by this <code>FontMetrics object.
*/
public int[] getWidths() {
int widths[] = new int[256];
for (char ch = 0 ; ch < 256 ; ch++) {
widths[ch] = charWidth(ch);
}
return widths;
}
/**
* Checks to see if the <code>Font has uniform line metrics. A
* composite font may consist of several different fonts to cover
* various character sets. In such cases, the
* <code>FontLineMetrics objects are not uniform.
* Different fonts may have a different ascent, descent, metrics and
* so on. This information is sometimes necessary for line
* measuring and line breaking.
* @return <code>true if the font has uniform line metrics;
* <code>false otherwise.
* @see java.awt.Font#hasUniformLineMetrics()
*/
public boolean hasUniformLineMetrics() {
return font.hasUniformLineMetrics();
}
/**
* Returns the {@link LineMetrics} object for the specified
* <code>String in the specified {@link Graphics} context.
* @param str the specified <code>String
* @param context the specified <code>Graphics context
* @return a <code>LineMetrics object created with the
* specified <code>String and Graphics context.
* @see java.awt.Font#getLineMetrics(String, FontRenderContext)
*/
public LineMetrics getLineMetrics( String str, Graphics context) {
return font.getLineMetrics(str, myFRC(context));
}
/**
* Returns the {@link LineMetrics} object for the specified
* <code>String in the specified {@link Graphics} context.
* @param str the specified <code>String
* @param beginIndex the initial offset of <code>str
* @param limit the end offset of <code>str
* @param context the specified <code>Graphics context
* @return a <code>LineMetrics object created with the
* specified <code>String and Graphics context.
* @see java.awt.Font#getLineMetrics(String, int, int, FontRenderContext)
*/
public LineMetrics getLineMetrics( String str,
int beginIndex, int limit,
Graphics context) {
return font.getLineMetrics(str, beginIndex, limit, myFRC(context));
}
/**
* Returns the {@link LineMetrics} object for the specified
* character array in the specified {@link Graphics} context.
* @param chars the specified character array
* @param beginIndex the initial offset of <code>chars
* @param limit the end offset of <code>chars
* @param context the specified <code>Graphics context
* @return a <code>LineMetrics object created with the
* specified character array and <code>Graphics context.
* @see java.awt.Font#getLineMetrics(char[], int, int, FontRenderContext)
*/
public LineMetrics getLineMetrics(char [] chars,
int beginIndex, int limit,
Graphics context) {
return font.getLineMetrics(
chars, beginIndex, limit, myFRC(context));
}
/**
* Returns the {@link LineMetrics} object for the specified
* {@link CharacterIterator} in the specified {@link Graphics}
* context.
* @param ci the specified <code>CharacterIterator
* @param beginIndex the initial offset in <code>ci
* @param limit the end index of <code>ci
* @param context the specified <code>Graphics context
* @return a <code>LineMetrics object created with the
* specified arguments.
* @see java.awt.Font#getLineMetrics(CharacterIterator, int, int, FontRenderContext)
*/
public LineMetrics getLineMetrics(CharacterIterator ci,
int beginIndex, int limit,
Graphics context) {
return font.getLineMetrics(ci, beginIndex, limit, myFRC(context));
}
/**
* Returns the bounds of the specified <code>String in the
* specified <code>Graphics context. The bounds is used
* to layout the <code>String.
* <p>Note: The returned bounds is in baseline-relative coordinates
* (see {@link java.awt.FontMetrics class notes}).
* @param str the specified <code>String
* @param context the specified <code>Graphics context
* @return a {@link Rectangle2D} that is the bounding box of the
* specified <code>String in the specified
* <code>Graphics context.
* @see java.awt.Font#getStringBounds(String, FontRenderContext)
*/
public Rectangle2D getStringBounds( String str, Graphics context) {
return font.getStringBounds(str, myFRC(context));
}
/**
* Returns the bounds of the specified <code>String in the
* specified <code>Graphics context. The bounds is used
* to layout the <code>String.
* <p>Note: The returned bounds is in baseline-relative coordinates
* (see {@link java.awt.FontMetrics class notes}).
* @param str the specified <code>String
* @param beginIndex the offset of the beginning of <code>str
* @param limit the end offset of <code>str
* @param context the specified <code>Graphics context
* @return a <code>Rectangle2D that is the bounding box of the
* specified <code>String in the specified
* <code>Graphics context.
* @see java.awt.Font#getStringBounds(String, int, int, FontRenderContext)
*/
public Rectangle2D getStringBounds( String str,
int beginIndex, int limit,
Graphics context) {
return font.getStringBounds(str, beginIndex, limit,
myFRC(context));
}
/**
* Returns the bounds of the specified array of characters
* in the specified <code>Graphics context.
* The bounds is used to layout the <code>String
* created with the specified array of characters,
* <code>beginIndex and limit.
* <p>Note: The returned bounds is in baseline-relative coordinates
* (see {@link java.awt.FontMetrics class notes}).
* @param chars an array of characters
* @param beginIndex the initial offset of the array of
* characters
* @param limit the end offset of the array of characters
* @param context the specified <code>Graphics context
* @return a <code>Rectangle2D that is the bounding box of the
* specified character array in the specified
* <code>Graphics context.
* @see java.awt.Font#getStringBounds(char[], int, int, FontRenderContext)
*/
public Rectangle2D getStringBounds( char [] chars,
int beginIndex, int limit,
Graphics context) {
return font.getStringBounds(chars, beginIndex, limit,
myFRC(context));
}
/**
* Returns the bounds of the characters indexed in the specified
* <code>CharacterIterator in the
* specified <code>Graphics context.
* <p>Note: The returned bounds is in baseline-relative coordinates
* (see {@link java.awt.FontMetrics class notes}).
* @param ci the specified <code>CharacterIterator
* @param beginIndex the initial offset in <code>ci
* @param limit the end index of <code>ci
* @param context the specified <code>Graphics context
* @return a <code>Rectangle2D that is the bounding box of the
* characters indexed in the specified <code>CharacterIterator
* in the specified <code>Graphics context.
* @see java.awt.Font#getStringBounds(CharacterIterator, int, int, FontRenderContext)
*/
public Rectangle2D getStringBounds(CharacterIterator ci,
int beginIndex, int limit,
Graphics context) {
return font.getStringBounds(ci, beginIndex, limit,
myFRC(context));
}
/**
* Returns the bounds for the character with the maximum bounds
* in the specified <code>Graphics context.
* @param context the specified <code>Graphics context
* @return a <code>Rectangle2D that is the
* bounding box for the character with the maximum bounds.
* @see java.awt.Font#getMaxCharBounds(FontRenderContext)
*/
public Rectangle2D getMaxCharBounds(Graphics context) {
return font.getMaxCharBounds(myFRC(context));
}
private FontRenderContext myFRC(Graphics context) {
if (context instanceof Graphics2D) {
return ((Graphics2D)context).getFontRenderContext();
}
return DEFAULT_FRC;
}
/**
* Returns a representation of this <code>FontMetrics
* object's values as a <code>String.
* @return a <code>String representation of this
* <code>FontMetrics object.
* @since JDK1.0.
*/
public String toString() {
return getClass().getName() +
"[font=" + getFont() +
"ascent=" + getAscent() +
", descent=" + getDescent() +
", height=" + getHeight() + "]";
}
/**
* Initialize JNI field and method IDs
*/
private static native void initIDs();
}
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