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本文主要介绍下java Color对象中的alpha值。

alpha

java/awt/Color.java

/**     * Creates an opaque sRGB color with the specified red, green,     * and blue values in the range (0 - 255).     * The actual color used in rendering depends     * on finding the best match given the color space     * available for a given output device.     * Alpha is defaulted to 255.     *     * @throws IllegalArgumentException if r, g     *        or b are outside of the range     *        0 to 255, inclusive     * @param r the red component     * @param g the green component     * @param b the blue component     * @see #getRed     * @see #getGreen     * @see #getBlue     * @see #getRGB     */    public Color(int r, int g, int b) {        this(r, g, b, 255);    }    /**     * Creates an sRGB color with the specified red, green, blue, and alpha     * values in the range (0 - 255).     *     * @throws IllegalArgumentException if r, g,     *        b or a are outside of the range     *        0 to 255, inclusive     * @param r the red component     * @param g the green component     * @param b the blue component     * @param a the alpha component     * @see #getRed     * @see #getGreen     * @see #getBlue     * @see #getAlpha     * @see #getRGB     */    @ConstructorProperties({"red", "green", "blue", "alpha"})    public Color(int r, int g, int b, int a) {        value = ((a & 0xFF) << 24) |                ((r & 0xFF) << 16) |                ((g & 0xFF) << 8)  |                ((b & 0xFF) << 0);        testColorValueRange(r,g,b,a);    }

java里头的color不指定alpha的话，默认其值为255，也就是没有透明度。

opacity

color对象里头的alpha其实是指不透明度，其值范围为0-255，越大越不透明。 其通常对应opacity，这个就是单词语义表达的不透明度，其值范围[0,1.0f]，值越大，越不透明。

opacity与alpha的映射

opacity与alpha之间的主要关系列表如下

100% — FF95% — F290% — E685% — D980% — CC75% — BF70% — B365% — A660% — 9955% — 8C50% — 8045% — 7340% — 6635% — 5930% — 4D25% — 4020% — 3315% — 2610% — 1A5% — 0D0% — 00

这个怎么转义呢，如下

int alpha = Math.round(opacity * 255);

再将int输出为十六进制的表示方式

String hex = Integer.toHexString(alpha).toUpperCase();        if (hex.length() == 1){            hex = "0" + hex;        }

不足两位往前不零

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