Java可以使用子像素AA渲染半透明文本吗？

Question

我发现，虽然在 Java（最新版本 6u23）中渲染不透明文本可以使用子像素 AA，但渲染半透明文本却不能。

子像素 AA：

仅颜色从 0xFFFFFFFF 更改为 0xBFFFFFFF 的相同文本：

< img src="https://i.sstatic.net/F3rlJ.gif" alt="alt text">

正如你所看到的，半透明文本显然是标准的 AA，而不是干净的半透明渲染，它有那么糟糕的 ' 90年代“蜘蛛侠”的外表。

这是由于子像素 AA 的技术限制，还是 Java 中的错误，或者只是因为 Java 甚至没有尝试半透明文本，或者我错过了什么？

---

图形初始化

dbGraphics=(Graphics2D)dbImage.getGraphics();
if(dctRoot.properties.getBoolean("Antialias",true)) {
    try {
        Map hnts=(Map)(dctRoot.awtComponent.getToolkit().getDesktopProperty("awt.font.desktophints"));

        // SET AA ON OVERALL (NOTE: GENERAL AA MUST BE OFF FOR SUBPIXEL AA TO BE HONORED - TEXT WIDGETS MUST DO THIS THEMSELVES)
        dbGraphics.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);

        if(hnts!=null) {
            // SET FONT RENDERING HINTS FROM DESKTOP
            dbGraphics.addRenderingHints(hnts);
            }
        else {
            try {
                // SET TEXT AA TO FONT-SPECIFIED GASP AA (JAVA 6+)
                dbGraphics.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING,RenderingHints.class.getField("VALUE_TEXT_ANTIALIAS_GASP").get(null));
                }
            catch(Throwable thr3) {
                // SET TEXT AA TO DEFAULT
                dbGraphics.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING,RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
                }
            }
        }
    catch(Throwable thr) {
        dctRoot.log.println("Antialiasing not supported on this JVM ("+thr+").");
        dctRoot.setProperty("Antialias","False");           // turn off AA for subsequent painting
        }
    }
else {
    try {
        dbGraphics.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_OFF);
        dbGraphics.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING,RenderingHints.VALUE_TEXT_ANTIALIAS_OFF);
        }
    catch(Throwable thr) {;}                                // ignore exception
    }

文本渲染

Object oaa=disableGeneralAA(gc);
...
gc.drawString(tl,xx,(ty+(xa*met.getHeight())));
restoreGeneralAA(gc,oaa);

...


static private volatile boolean         hasRenderingHints=true;

// *****************************************************************************
// STATIC INIT & MAIN
// *****************************************************************************

// *****************************************************************************
// STATIC METHODS
// *****************************************************************************

/**
 * Disable the general anti-aliasing rendering hint, returning whether the old value was RenderingHints.VALUE_ANTIALIAS_ON.
 * <p>
 * This method is needed for text rendering due to a bug in AWT; as of Java 6_20 when general AA is on text is not rendered using subpixel
 * AA, so general AA has to be turned off before rendering text and turned back on when done.  This method abstracts that work and deals
 * with the possibility that the JVM does not support rendering hints, such as is the case with JME JVMs.
 */
static public Object disableGeneralAA(Graphics2D gc) {
    Object                              old=null;

    if(hasRenderingHints) {
        try {
            old=gc.getRenderingHint(RenderingHints.KEY_ANTIALIASING);
            gc.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_OFF);
            }
        catch(NoClassDefFoundError thr) { hasRenderingHints=false; }
        catch(NoSuchFieldError     thr) { hasRenderingHints=false; }
        catch(NoSuchMethodError    thr) { hasRenderingHints=false; }
        }
    return old;
    }

/**
 * Disable the general anti-aliasing rendering hint, returning whether the old value was RenderingHints.VALUE_ANTIALIAS_ON.
 * <p>
 * This method is needed for text rendering due to a bug in AWT; as of Java 6_20 when general AA is on text is not rendered using subpixel
 * AA, so general AA has to be turned off before rendering text and turned back on when done.  This method abstracts that work and deals
 * with the possibility that the JVM does not support rendering hints, such as is the case with JME JVMs.
 */
static public void restoreGeneralAA(Graphics2D gc, Object val) {
    Object                              old=null;

    if(hasRenderingHints && val!=null) {
        try { gc.setRenderingHint(RenderingHints.KEY_ANTIALIASING,val); }
        catch(NoClassDefFoundError thr) { hasRenderingHints=false; }
        catch(NoSuchFieldError     thr) { hasRenderingHints=false; }
        catch(NoSuchMethodError    thr) { hasRenderingHints=false; }
        }
    }

Answer 1

似乎不（完全）支持将文本渲染到透明背景，从这些错误报告中可以看出：

• https://bugs.java.com/bugdatabase/view_bug?bug_id=6728834
• https://bugs.java.com/bugdatabase/view_bug?bug_id=6749060
• https://bugs.java.com/bugdatabase/view_bug?bug_id=6749069

Answer 2

我认为这是因为你使用了 GASP，它从字体样式中获取了点。您是否尝试过使用VALUE_TEXT_ANTIALIAS_DEFAULT和VALUE_ALPHA_INTERPOLATION_DEFAULT？值得一试。

http://download.oracle.com/javase/6 /docs/api/java/awt/RenderingHints.html

Answer 3

您使用什么 Java 版本？你不说。但显然这个问题已在 Java 6 update 12 (J6u12) 或 JDK7 b43 中得到修复

请参见此处：
https://bugs.java.com/bugdatabase/view_bug?bug_id=6749060

如果您使用 Java = 或高于 J6u12 再次进行测试，但仍然发现该错误，您可以在 Sun 的错误数据库中的 RFE 中进行评论。

在 Java 平台中解决问题的方法是：

1. 在 Sun 的 BugParade 上对错误报告进行投票，以提高其优先级，并等待 Sun/Oracle 程序员处理它
   或者
2. 既然 Java 是开源的，那就自己修复吧。 （加入 ho.io/jkp5 的邮件列表:-)

您想要投票或评论的 Bugparade 报告在这里（如果您使用 j6u12 进行测试，它仍然存在）是
url：ho.io/jkp2

如果您想实现一个已知的解决方法，以便即使在较旧的 JRE 中文本也看起来不错，这里提供了一个

解决方法url：ho.io/jkpy

“看起来像我正在使用的解决方案通过将所需的前景色与组件的背景色混合来模拟半透明度仍然是确保使用本机光栅器的方法。”

祝你好运！