How to maintain multi layers of ImageViews and keep their aspect ratio based on the largest one?

Question

Suppose I have multiple Images that I need to put one on top of the other, some might have some kind of animation appearing and some might even be draggable.

the largest one which usually takes the whole screen would be the bottom in the Z-coordinate (let's call it the backgroundImageView ), while all of the rest appear on top of it (and on top of others).

like so:

• backgroundImageView
• imageView1 , centered.
• imageView2 , at 60%,60% of the top left corner
• ...

If I use a FrameLayout (which seems like the best solution), the backgroundImageView would have its size fit nicely, but how can I force the other layers resize themselves accordingly?

I think I need to somehow get where to put the other layers and how to set their sizes.

The easy way is to make sure all layers have the exact same size, but that could take a lot of memory and become very slow when animating or dragging views. It would be a huge waste if some of the layers have a very small content.

Answer 1

this is a class that displays an image with additional layers:

import java.util.ArrayList;
import java.util.Iterator;

import android.content.Context;
import android.content.res.Resources;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Rect;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.net.Uri;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.Log;
import android.util.TypedValue;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.view.animation.Transformation;
import android.widget.ImageView;

public class LayeredImageView extends ImageView {
    private final static String TAG = "LayeredImageView";

    private ArrayList<Layer> mLayers;
    private Matrix mDrawMatrix;

    private Resources mResources;

    public LayeredImageView(Context context) {
        super(context);
        init();
    }

    public LayeredImageView(Context context, AttributeSet set) {
        super(context, set);
        init();

        int[] attrs = {
                android.R.attr.src
        };
        TypedArray a = context.obtainStyledAttributes(set, attrs);
        TypedValue outValue = new TypedValue();
        if (a.getValue(0, outValue)) {
            setImageResource(outValue.resourceId);
        }
        a.recycle();
    }

    private void init() {
        mLayers = new ArrayList<Layer>();
        mDrawMatrix = new Matrix();
        mResources = new LayeredImageViewResources();
    }

    @Override
    protected boolean verifyDrawable(Drawable dr) {
        for (int i = 0; i < mLayers.size(); i++) {
            Layer layer = mLayers.get(i);
            if (layer.drawable == dr) {
                return true;
            }
        }
        return super.verifyDrawable(dr);
    }

    @Override
    public void invalidateDrawable(Drawable dr) {
        if (verifyDrawable(dr)) {
            invalidate();
        } else {
            super.invalidateDrawable(dr);
        }
    }

    @Override
    public Resources getResources() {
        return mResources;
    }

    @Override
    public void setImageBitmap(Bitmap bm) throws RuntimeException {
        String detailMessage = "setImageBitmap not supported, use: setImageDrawable() " +
                "or setImageResource()";
        throw new RuntimeException(detailMessage);
    }

    @Override
    public void setImageURI(Uri uri) throws RuntimeException {
        String detailMessage = "setImageURI not supported, use: setImageDrawable() " +
                "or setImageResource()";
        throw new RuntimeException(detailMessage);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Matrix matrix = getImageMatrix();
        if (matrix != null) {
            int numLayers = mLayers.size();
            boolean pendingAnimations = false;
            for (int i = 0; i < numLayers; i++) {
                mDrawMatrix.set(matrix);
                Layer layer = mLayers.get(i);
                if (layer.matrix != null) {
                    mDrawMatrix.preConcat(layer.matrix);
                }
                if (layer.animation == null) {
                    draw(canvas, layer.drawable, mDrawMatrix, 255);
                } else {
                    Animation a = layer.animation;
                    if (!a.isInitialized()) {
                        Rect bounds = layer.drawable.getBounds();
                        Drawable parentDrawable = getDrawable();
                        if (parentDrawable != null) {
                            Rect parentBounds = parentDrawable.getBounds();
                            a.initialize(bounds.width(), bounds.height(), parentBounds.width(), parentBounds.height());
                        } else {
                            a.initialize(bounds.width(), bounds.height(), 0, 0);
                        }
                    }
                    long currentTime = AnimationUtils.currentAnimationTimeMillis();
                    boolean running = a.getTransformation(currentTime, layer.transformation);
                    if (running) {
                        // animation is running: draw animation frame
                        Matrix animationFrameMatrix = layer.transformation.getMatrix();
                        mDrawMatrix.preConcat(animationFrameMatrix);

                        int alpha = (int) (255 * layer.transformation.getAlpha());
//    Log.d(TAG, "onDraw ********** [" + i + "], alpha: " + alpha + ", matrix: " + animationFrameMatrix);
                        draw(canvas, layer.drawable, mDrawMatrix, alpha);
                        pendingAnimations = true;
                    } else {
                        // animation ended: set it to null
                        layer.animation = null;
                        draw(canvas, layer.drawable, mDrawMatrix, 255);
                    }
                }
            }
            if (pendingAnimations) {
                // invalidate if any pending animations
                invalidate();
            }
        }
    }

    private void draw(Canvas canvas, Drawable drawable, Matrix matrix, int alpha) {
        canvas.save(Canvas.MATRIX_SAVE_FLAG);
        canvas.concat(matrix);
        drawable.setAlpha(alpha);
        drawable.draw(canvas);
        canvas.restore();
    }

    public Layer addLayer(Drawable d, Matrix m) {
        Layer layer = new Layer(d, m);
        mLayers.add(layer);
        invalidate();
        return layer;
    }

    public Layer addLayer(Drawable d) {
        return addLayer(d, null);
    }

    public Layer addLayer(int idx, Drawable d, Matrix m) {
        Layer layer = new Layer(d, m);
        mLayers.add(idx, layer);
        invalidate();
        return layer;
    }

    public Layer addLayer(int idx, Drawable d) {
        return addLayer(idx, d, null);
    }

    public void removeLayer(Layer layer) {
        layer.valid = false;
        mLayers.remove(layer);
    }

    public void removeAllLayers() {
        Iterator<Layer> iter = mLayers.iterator();
        while (iter.hasNext()) {
            LayeredImageView.Layer layer = iter.next();
            layer.valid = false;
            iter.remove();
        }
        invalidate();
    }

    public int getLayersSize() {
        return mLayers.size();
    }

    public class Layer {
        private Drawable drawable;
        private Animation animation;
        private Transformation transformation;
        private Matrix matrix;
        private boolean valid;

        private Layer(Drawable d, Matrix m) {
            drawable = d;
            transformation = new Transformation();
            matrix = m;
            valid = true;
            Rect bounds = d.getBounds();
            if (bounds.isEmpty()) {
                if (d instanceof BitmapDrawable) {
                    int right = d.getIntrinsicWidth();
                    int bottom = d.getIntrinsicHeight();
                    d.setBounds(0, 0, right, bottom);
                } else {
                    String detailMessage = "drawable bounds are empty, use d.setBounds()";
                    throw new RuntimeException(detailMessage);
                }
            }
            d.setCallback(LayeredImageView.this);
        }

        public void startLayerAnimation(Animation a) throws RuntimeException {
            if (!valid) {
                String detailMessage = "this layer has already been removed";
                throw new RuntimeException(detailMessage);
            }
            transformation.clear();
            animation = a;
            if (a != null) {
                a.start();
            }
            invalidate();
        }

        public void stopLayerAnimation(int idx) throws RuntimeException {
            if (!valid) {
                String detailMessage = "this layer has already been removed";
                throw new RuntimeException(detailMessage);
            }
            if (animation != null) {
                animation = null;
                invalidate();
            }
        }
    }

    private class LayeredImageViewResources extends Resources {

        public LayeredImageViewResources() {
            super(getContext().getAssets(), new DisplayMetrics(), null);
        }

        @Override
        public Drawable getDrawable(int id) throws NotFoundException {
            Drawable d = super.getDrawable(id);
            if (d instanceof BitmapDrawable) {
                BitmapDrawable bd = (BitmapDrawable) d;
                bd.getBitmap().setDensity(DisplayMetrics.DENSITY_DEFAULT);
                bd.setTargetDensity(DisplayMetrics.DENSITY_DEFAULT);
            }
            return d;
        }
    }
}

and how it can be used:

    final LayeredImageView v = new LayeredImageView(this);
    Resources res = v.getResources();

    v.setImageResource(R.drawable.background);

    Matrix m;

    m = new Matrix();
    m.preTranslate(81, 146); // pixels to offset
    final Layer layer1 = v.addLayer(res.getDrawable(R.drawable.layer1), m);

    m = new Matrix();
    m.preTranslate(62, 63); // pixels to offset
    final Layer layer0 = v.addLayer(0, res.getDrawable(R.drawable.layer0), m);


    final AnimationDrawable ad = new AnimationDrawable();
    ad.setOneShot(false);
    Drawable frame1, frame2;
    frame1 = res.getDrawable(R.drawable.layer0);
    frame2 = res.getDrawable(R.drawable.layer1);
    ad.addFrame(frame1, 3000);
    ad.addFrame(frame2, 1000);
    ad.addFrame(frame1, 250);
    ad.addFrame(frame2, 250);
    ad.addFrame(frame1, 250);
    ad.addFrame(frame2, 250);
    ad.addFrame(frame1, 250);
    ad.addFrame(frame2, 250);
    ad.setBounds(200, 20, 300, 120);
    v.addLayer(1, ad);
    v.post(new Runnable() {
        @Override
        public void run() {
            ad.start();
        }
    });

    int[] colors = {
            0xeeffffff,
            0xee0038a8,
            0xeece1126,
    };
    GradientDrawable gd = new GradientDrawable(Orientation.TOP_BOTTOM, colors);
    gd.setBounds(0, 0, 100, 129);
    gd.setCornerRadius(20);
    gd.setStroke(5, 0xaa666666);
    final Matrix mm = new Matrix();
    mm.preTranslate(200, 69); // pixels to offset
    mm.preRotate(20, 50, 64.5f);
    final Layer layer2 = v.addLayer(2, gd, mm);

    final Animation as = AnimationUtils.loadAnimation(this, R.anim.anim_set);

    final Runnable action1 = new Runnable() {
        @Override
        public void run() {
            Animation a;
            Interpolator i;

            i = new Interpolator() {
                @Override
                public float getInterpolation(float input) {
                    return (float) Math.sin(input * Math.PI);
                }
            };
            as.setInterpolator(i);
            layer0.startLayerAnimation(as);

            a = new TranslateAnimation(0, 0, 0, 100);
            a.setDuration(3000);
            i = new Interpolator() {
                @Override
                public float getInterpolation(float input) {
                    float output = (float) Math.sin(Math.pow(input, 2.5f) * 12 * Math.PI);
                    return (1-input) * output;
                }
            };
            a.setInterpolator(i);
            layer1.startLayerAnimation(a);

            a = new AlphaAnimation(0, 1);
            i = new Interpolator() {
                @Override
                public float getInterpolation(float input) {
                    return (float) (1 - Math.sin(input * Math.PI));
                }
            };
            a.setInterpolator(i);
            a.setDuration(2000);
            layer2.startLayerAnimation(a);
        }
    };
    OnClickListener l1 = new OnClickListener() {
        @Override
        public void onClick(View view) {
            action1.run();
        }
    };
    v.setOnClickListener(l1);
    v.postDelayed(action1, 2000);

//    final float[] values = new float[9];
//    final float[] pts = new float[2];
//    final Matrix inverse = new Matrix();;
//    OnTouchListener l = new OnTouchListener() {
//        @Override
//        public boolean onTouch(View view, MotionEvent event) {
//            int action = event.getAction();
//            if (action != MotionEvent.ACTION_UP) {
//                if (inverse.isIdentity()) {
//                    v.getImageMatrix().invert(inverse);
//                    Log.d(TAG, "onTouch set inverse");
//                }
//                pts[0] = event.getX();
//                pts[1] = event.getY();
//                inverse.mapPoints(pts);
//
//                mm.getValues(values);
//                // gd's bounds are (0, 0, 100, 129);
//                values[Matrix.MTRANS_X] = pts[0] - 100 / 2;
//                values[Matrix.MTRANS_Y] = pts[1] - 129 / 2;
//                mm.setValues(values);
//                v.invalidate();
//            }
//            return false;
//        }
//    };
//    v.setOnTouchListener(l);
    setContentView(v);

anim_set.xml looks like:

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android"
    android:shareInterpolator="true"
>
    <rotate
        android:fromDegrees="0"
        android:toDegrees="30"
        android:pivotX="50%"
        android:pivotY="50%"
        android:duration="2500"
    />
    <scale
        android:fromXScale="1"
        android:toXScale="1.8"
        android:fromYScale="1"
        android:toYScale="1.8"
        android:pivotX="50%"
        android:pivotY="50%"
        android:duration="2500"
    />
</set>

with the following images:

background.png:

layer0.png:

layer1.png:

the result is:

IMPORTANT in order to prevent resources from auto OS scaling when loading from different drawable-* folders you have to use Resources object obtained from LayeredImageView.getResources() method

have fun!

Answer 2

just extend ImageView and override its onDraw method in order to draw additional layers

this is a minimal varsion (enhanced version with animations is in the second answer):

import java.util.ArrayList;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.util.AttributeSet;
import android.util.Log;
import android.widget.ImageView;

public class LayeredImageView extends ImageView {
    private final static String TAG = "LayeredImageView";

    ArrayList<Bitmap> mLayers;

    public LayeredImageView(Context context) {
        super(context);
        init();
    }

    public LayeredImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        mLayers = new ArrayList<Bitmap>();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Matrix matrix = getImageMatrix();
        if (matrix != null) {
            int numLayers = mLayers.size();
            for (int i = 0; i < numLayers; i++) {
                Bitmap b = mLayers.get(i);
                canvas.drawBitmap(b, matrix, null);
            }
        }
    }

    public void addLayer(Bitmap b) {
        mLayers.add(b);
        invalidate();
    }

    public void addLayer(int idx, Bitmap b) {
        mLayers.add(idx, b);
        invalidate();
    }

    public void removeLayer(int idx) {
        mLayers.remove(idx);
    }

    public void removeAllLayers() {
        mLayers.clear();
        invalidate();
    }

    public int getLayersSize() {
        return mLayers.size();
    }
}

and how its used in your Activity:

LayeredImageView v = new LayeredImageView(this);
v.setImageResource(R.drawable.background);
Resources res = getResources();
v.addLayer(BitmapFactory.decodeResource(res, R.drawable.layer0));
v.addLayer(0, BitmapFactory.decodeResource(res, R.drawable.layer1));
setContentView(v);

here you have 3 images:

background.png

layer0.png

layer1.png

and three above combined

and finally the captured screen from the emulator