Scale image keeping its aspect ratio in background drawable

Question

How do I make a background image fit the view but keep its aspect ratio when using <bitmap /> as a background drawable XML? None of <bitmap>'s android:gravity values gives the desired effect.

Solution 1

It is impossible to achieve manipulating background attribute within xml-files only. There are two options:

1. You cut/scale the bitmap programmatically with Bitmap.createScaledBitmap(Bitmap src, int dstWidth, int dstHeight, boolean filter) and set it as some View's background.

2. You use ImageView instead of background placing it as the first layout's element and specify android:scaleType attribute for it:

   <RelativeLayout
       android:layout_width="fill_parent"
       android:layout_height="fill_parent" >
   
       <ImageView
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
   
           android:src="@drawable/backgrnd"
           android:scaleType="centerCrop" />
   
       ...
   
       rest layout components here
   
       ...
   
   </RelativeLayout>
   

Solution 2

There is an easy way to do this from the drawable:

your_drawable.xml

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >

    <item android:drawable="@color/bg_color"/>
    <item>
        <bitmap
            android:gravity="center|bottom|clip_vertical"
            android:src="@drawable/your_image" />
    </item>

</layer-list>

The only downside is that if there is not enough space, your image won't be fully shown, but it will be clipped, I couldn't find an way to do this directly from a drawable. But from the tests I did it works pretty well, and it doesn't clip that much of the image. You could play more with the gravity options.

Another way will be to just create an layout, where you will use an ImageView and set the scaleType to fitCenter.

Hope this information helps you achieve what you want.

Solution 3

I wanted to do something similar in my custom Drawable class. Here are the important pieces:

public class CustomBackgroundDrawable extends Drawable
{
    private Rect mTempRect = new Rect();
    private Paint mBitmapPaint = new Paint(Paint.ANTI_ALIAS_FLAG);

    ...

public void draw(@NonNull Canvas canvas)
{
    Rect bounds = getBounds();
    if (mBitmap != null ) {
        if (mScaleType == ScaleType.SCALE_FILL) {
            //bitmap scales to fill the whole bounds area (bitmap can be cropped)
            if (bounds.height() > 0 && bounds.height() > 0) {
                float scale = Math.min(mBitmap.getWidth()/(float)bounds.width(), mBitmap.getHeight()/(float)bounds.height());

                float bitmapVisibleWidth = scale * bounds.width();
                float bitmapVisibleHeight = scale * bounds.height();

                mTempRect.set((int)(mBitmap.getWidth()-bitmapVisibleWidth)/2, 0, (int)(bitmapVisibleWidth+mBitmap.getWidth())/2, (int)bitmapVisibleHeight);
                canvas.drawBitmap(mBitmap, mTempRect, bounds, mBitmapPaint);
            }
        } else if (mScaleType == ScaleType.SCALE_FIT) {
            //bitmap scales to fit in bounds area
            if (bounds.height() > 0 && bounds.height() > 0) {
                float scale = Math.min((float)bounds.width()/mBitmap.getWidth(), (float)bounds.height()/mBitmap.getHeight());

                float bitmapScaledWidth = scale * mBitmap.getWidth();
                float bitmapScaledHeight = scale * mBitmap.getHeight();
                int centerPadding = (int)(bounds.width()-bitmapScaledWidth)/2;
                mTempRect.set(bounds.left + centerPadding, bounds.top, bounds.right - centerPadding, bounds.top+(int)bitmapScaledHeight);
                canvas.drawBitmap(mBitmap, null, mTempRect, mBitmapPaint);
            }
        }
    }
}

With this approach you are flexible to apply any scale logic that you need

Solution 4

Another approach would be to create patch 9 images of your regular image and have it stretch scale the way you want it to.

You could have it center the content by putting 9-patch-dots in the corners that will preserve your ratio obviously (assuming the outer most edge of your image is repeatable/transparent).

Hopefully you get the idea.

Solution 5

If your bitmap is wider than it is tall, use android:gravity="fill_vertical". Otherwise, use android:gravity="fill_horizontal". This has a similar effect as using android:scaleType="centerCrop" on an ImageView.

<bitmap xmlns:android="http://schemas.android.com/apk/res/android"
    android:gravity="fill_vertical"
    android:src="@drawable/image" />

If you support multiple orientations, you can create one bitmap XML file in the drawable-port folder and the other in the drawable-land folder.

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Comments

[tilex]

All possible android:scaleType values don't give the needed effect. An image fit the view keeping its aspect ratio only if I don't specify scaleType at all.

[Father Stack]

and here you can see some examples for each type: etcodehome.blogspot.de/2011/05/…

[Dmitry]

Unfortunately, it doesn't work with android:background.

[J. Hesters]

This keeps the image unscaled and small and only displays it at the bottom.

[Ionut Negru]

Indeed, if you need to scale it, other solutions are more appropriate. As you see, the properties do not refer to any type of scaling.

[Firzen]

This does not answer the question.