序
本文主要介紹下java Color對象中的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 <code>r</code>, <code>g</code>
* or <code>b</code> 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 <code>r</code>, <code>g</code>,
* <code>b</code> or <code>a</code> 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里頭的color不指定alpha的話，默認其值為255，也就是沒有透明度。
opacity
color對象里頭的alpha其實是指不透明度，其值范圍為0-255，越大越不透明。
其通常對應opacity，這個就是單詞語義表達的不透明度，其值范圍[0,1.0f]，值越大，越不透明。
opacity與alpha的映射
opacity與alpha之間的主要關系列表如下
100% — FF
95% — F2
90% — E6
85% — D9
80% — CC
75% — BF
70% — B3
65% — A6
60% — 99
55% — 8C
50% — 80
45% — 73
40% — 66
35% — 59
30% — 4D
25% — 40
20% — 33
15% — 26
10% — 1A
5% — 0D
0% — 00
這個怎么轉義呢，如下
int alpha = Math.round(opacity * 255);
再將int輸出為十六進制的表示方式
String hex = Integer.toHexString(alpha).toUpperCase();
if (hex.length() == 1){
hex = "0" + hex;
}
不足兩位往前不零
