操纵阿尔法字节的Java / Android的颜色INT [英] Manipulate alpha bytes of Java/Android color int

问题描述

如果我有Java的一个int，我使用的是Android颜色（在画布绘画），我该如何处理这个int只是alpha分量？例如，我该如何使用的操作做到这一点：

If I have an int in Java that I'm using as an Android color (for drawing on a Canvas), how do I manipulate just the alpha component of that int? For example, how can I use an operation to do this:

int myOpaqueColor = 0xFFFFFF;
float factor = 0;
int myTransparentColor = operationThatChangesAlphaBytes(myOpaqueColor, factor);
//myTransparentColor should now = 0x00FFFFFF;

在理想情况下，这将是很好用任何系数比刚才设置的字节静态值乘的第一个字节，而

Ideally, it would be nice to multiply those first bytes by whatever factor is, rather than just set the bytes to a static value.

推荐答案

查看颜色类。

您code看起来有点这样的事情。

Your code would look a bit something like this.

int color = 0xFFFFFFFF;
int transparent = Color.argb(0, Color.red(color), Color.green(color), Color.blue(color));

所以，包装在一个方法可能如下：

So wrapping it in a method might look like:

public int adjustAlpha(int color, float factor) {
    int alpha = Math.round(Color.alpha(color) * factor);
    int red = Color.red(color);
    int green = Color.green(color);
    int blue = Color.blue(color);
    return Color.argb(alpha, red, green, blue);
}

然后把它设置透明度，让我们说，50％：

And then call it to set the transparency to, let's say, 50%:

int halfTransparentColor = adjustAlpha(0xFFFFFFFF, 0.5f);

我想使用所提供的Color类是多一点点的自我记录，只是自己做位操作，再加上它已经为你做了。

I think using the provided Color class is a little bit more self-documenting that just doing the bit manipulation yourself, plus it's already done for you.

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