Android: Make specific (green) color in background

问题:

i am writing an app for Android.

in an xml file defining layout I have a TabHost with 6 Tabs, which all have the same big background image "settingsdlg.gif".

<TabHost xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@android:id/tabhost" 
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" 
    android:background="@drawable/settingsdlg" >
..

In styles.xml I specify that the window must be transparent:

<resources>
    <style name="my_app_style"  parent="@android:style/Theme.Dialog">
        <item name="android:windowNoTitle">true</item>
        <item name="android:windowBackground">@android:color/transparent</item>
    </style>

The problem is that the background image "settingsdlg.gif" is a rounded rect, and the small areas at the edges, which should be transparent, are green.

I know that to use transparency in images on Android, the images must be in PNG format, and the pixels i want transparent should be saved in PNG as transparent.

Unfortunately I get the images from a database and I can't change them, because they are also used in some other application for Win32 and Mac.

Is there a way to tell Android that in the background image the green pixels should be rendered transparent?

Thanks!

回答1:

You would have to change every green pixel into a transparent one. Here is an example: How to change colors of a Drawable in Android?

However if there are green pixels in the middle of the image then you can have a problem. So the other way is, if your image has constant size and shape, to create a mask and use xfer modes to create a new image with transparent rounded corners.

回答2:

Just if anyone had the same problem, here is the code:

//remove green edges from bg image
    Bitmap bgBitmap = ((BitmapDrawable)getResources().getDrawable(R.drawable.settingsdlg)).getBitmap();
    Bitmap transparentBgBitmap = Utils.getBitmapWithTransparentBG(bgBitmap, Color.GREEN);
    tabHost.setBackgroundDrawable(new BitmapDrawable(transparentBgBitmap));

in Utils:

public static Bitmap getBitmapWithTransparentBG(Bitmap srcBitmap, int bgColor) {
    Bitmap result = srcBitmap.copy(Bitmap.Config.ARGB_8888, true);
    int nWidth = result.getWidth();
    int nHeight = result.getHeight();
    for (int y = 0; y < nHeight; ++y)
      for (int x = 0; x < nWidth; ++x) {
    int nPixelColor = result.getPixel(x, y);
    if (nPixelColor == bgColor)
      result.setPixel(x, y, Color.TRANSPARENT);
      }
    return result;
}

回答3:

This code snippet worked for me:

PorterDuffColorFilter porterDuffColorFilter = new PorterDuffColorFilter(
    getResources().getColor(R.color.your_color),
    PorterDuff.Mode.MULTIPLY
);
imgView.getDrawable().setColorFilter(porterDuffColorFilter);
imgView.setBackgroundColor(Color.TRANSPARENT);