Java可以使用子像素AA渲染半透明文本吗？ [英] Can Java render translucent text using sub-pixel AA?

问题描述

我发现虽然在Java中渲染不透明文本（最新版本6u23）使用子像素AA就好了，渲染半透明文本却没有。

I have found that while rendering opaque text in Java (latest version 6u23) uses sub-pixel AA just fine, rendering translucent text does not.

子像素AA：

同样的文字，其中只有颜色已从0xFFFFFFFF到0xBFFFFFFF：

The same text for which only the color has been changed from 0xFFFFFFFF to 0xBFFFFFFF:

如您所见，半透明文字清晰明了标准AA而不是干净的半透明渲染，它具有可怕的'90年代蜘蛛外观。

As you can see, the translucent text is clearly standard AA and rather than a clean translucent rendering, it has that awful '90s "spidery" appearance.

这是否是由于子像素AA的技术限制，或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？

Is this due to a technical limitation for sub-pixel AA in general, or a bug in Java, or just because Java doesn't even try for translucent text, or have I missed something?

图形初始化on

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
    }

文字渲染

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; }
        }
    }

推荐答案

从这些错误报告中可以看出，似乎没有（完全）支持向透明背景渲染文本：

It seems rendering text to a transparant background is not (fully) supported, as can be seen from these bugreports:

• http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6728834


• http：//bugs.sun .com / bugdatabase / view_bug.do？bug_id = 6749060


• http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6749069

• http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6728834
• http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6749060
• http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6749069

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