Glide compatible fast blur bitmap transformation.

BlurTransform.java

package com.bandlab.bandlab.transformation;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffColorFilter;
import android.support.annotation.ColorRes;

import com.bumptech.glide.load.engine.bitmap_recycle.BitmapPool;
import com.bumptech.glide.load.resource.bitmap.BitmapTransformation;

/**
 * Glide transformation class for blur bitmap
 */
public class BlurTransform extends BitmapTransformation {

    public static final String TRANSFORMATION_ID = "com.bandlab.bandlab.BlurTransform";
    public static final int DEFAULT_SCALE_FACTOR = 5;
    private static final int DEFAULT_BLUR_RADIUS = 21;
    private static final int DEFAULT_FOREGROUND = Color.WHITE;
    private final Context context;
    private
    @ColorRes
    int foregroundColor;
    private int blurRadius;
    private int scaleFactor = DEFAULT_SCALE_FACTOR;

    public BlurTransform(Context context) {
        this(DEFAULT_BLUR_RADIUS, context);
    }

    public BlurTransform(int blurRadius, Context context) {
        this(blurRadius, DEFAULT_FOREGROUND, context);
    }

    public BlurTransform(int blurRadius, @ColorRes int foregroundColor, Context context) {
        super(context);
        this.blurRadius = (int) (blurRadius * context.getResources().getDisplayMetrics().density);
        this.foregroundColor = foregroundColor;
        this.context = context;
        setScaleFactor(DEFAULT_SCALE_FACTOR);
    }

    public static Bitmap getBluredBitmapFastBlur(Bitmap sentBitmap, int radius) {

        // Stack Blur v1.0 from
        // http://www.quasimondo.com/StackBlurForCanvas/StackBlurDemo.html
        //
        // Java Author: Mario Klingemann <mario at quasimondo.com>
        // http://incubator.quasimondo.com
        // created Feburary 29, 2004
        // Android port : Yahel Bouaziz <yahel at kayenko.com>
        // http://www.kayenko.com
        // ported april 5th, 2012

        // This is a compromise between Gaussian Blur and Box blur
        // It creates much better looking blurs than Box Blur, but is
        // 7x faster than my Gaussian Blur implementation.
        //
        // I called it Stack Blur because this describes best how this
        // filter works internally: it creates a kind of moving stack
        // of colors whilst scanning through the image. Thereby it
        // just has to add one new block of color to the right side
        // of the stack and remove the leftmost color. The remaining
        // colors on the topmost layer of the stack are either added on
        // or reduced by one, depending on if they are on the right or
        // on the left side of the stack.
        //
        // If you are using this algorithm in your code please add
        // the following line:
        //
        // Stack Blur Algorithm by Mario Klingemann <[email protected]>

        if (radius < 1) {
            return (null);
        }

        int w = sentBitmap.getWidth();
        int h = sentBitmap.getHeight();

        int[] pix = new int[w * h];
        sentBitmap.getPixels(pix, 0, w, 0, 0, w, h);

        int wm = w - 1;
        int hm = h - 1;
        int wh = w * h;
        int div = radius + radius + 1;

        int r[] = new int[wh];
        int g[] = new int[wh];
        int b[] = new int[wh];
        int rsum, gsum, bsum, x, y, i, p, yp, yi, yw;
        int vmin[] = new int[Math.max(w, h)];

        int divsum = (div + 1) >> 1;
        divsum *= divsum;
        int dv[] = new int[256 * divsum];
        for (i = 0; i < 256 * divsum; i++) {
            dv[i] = (i / divsum);
        }

        yw = yi = 0;

        int[][] stack = new int[div][3];
        int stackpointer;
        int stackstart;
        int[] sir;
        int rbs;
        int r1 = radius + 1;
        int routsum, goutsum, boutsum;
        int rinsum, ginsum, binsum;

        for (y = 0; y < h; y++) {
            rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;
            for (i = -radius; i <= radius; i++) {
                p = pix[yi + Math.min(wm, Math.max(i, 0))];
                sir = stack[i + radius];
                sir[0] = (p & 0xff0000) >> 16;
                sir[1] = (p & 0x00ff00) >> 8;
                sir[2] = (p & 0x0000ff);
                rbs = r1 - Math.abs(i);
                rsum += sir[0] * rbs;
                gsum += sir[1] * rbs;
                bsum += sir[2] * rbs;
                if (i > 0) {
                    rinsum += sir[0];
                    ginsum += sir[1];
                    binsum += sir[2];
                } else {
                    routsum += sir[0];
                    goutsum += sir[1];
                    boutsum += sir[2];
                }
            }
            stackpointer = radius;

            for (x = 0; x < w; x++) {

                r[yi] = dv[rsum];
                g[yi] = dv[gsum];
                b[yi] = dv[bsum];

                rsum -= routsum;
                gsum -= goutsum;
                bsum -= boutsum;

                stackstart = stackpointer - radius + div;
                sir = stack[stackstart % div];

                routsum -= sir[0];
                goutsum -= sir[1];
                boutsum -= sir[2];

                if (y == 0) {
                    vmin[x] = Math.min(x + radius + 1, wm);
                }
                p = pix[yw + vmin[x]];

                sir[0] = (p & 0xff0000) >> 16;
                sir[1] = (p & 0x00ff00) >> 8;
                sir[2] = (p & 0x0000ff);

                rinsum += sir[0];
                ginsum += sir[1];
                binsum += sir[2];

                rsum += rinsum;
                gsum += ginsum;
                bsum += binsum;

                stackpointer = (stackpointer + 1) % div;
                sir = stack[(stackpointer) % div];

                routsum += sir[0];
                goutsum += sir[1];
                boutsum += sir[2];

                rinsum -= sir[0];
                ginsum -= sir[1];
                binsum -= sir[2];

                yi++;
            }
            yw += w;
        }
        for (x = 0; x < w; x++) {
            rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;
            yp = -radius * w;
            for (i = -radius; i <= radius; i++) {
                yi = Math.max(0, yp) + x;

                sir = stack[i + radius];

                sir[0] = r[yi];
                sir[1] = g[yi];
                sir[2] = b[yi];

                rbs = r1 - Math.abs(i);

                rsum += r[yi] * rbs;
                gsum += g[yi] * rbs;
                bsum += b[yi] * rbs;

                if (i > 0) {
                    rinsum += sir[0];
                    ginsum += sir[1];
                    binsum += sir[2];
                } else {
                    routsum += sir[0];
                    goutsum += sir[1];
                    boutsum += sir[2];
                }

                if (i < hm) {
                    yp += w;
                }
            }
            yi = x;
            stackpointer = radius;
            for (y = 0; y < h; y++) {
                // Preserve alpha channel: ( 0xff000000 & pix[yi] )
                pix[yi] = (0xff000000 & pix[yi]) | (dv[rsum] << 16) | (dv[gsum] << 8) | dv[bsum];

                rsum -= routsum;
                gsum -= goutsum;
                bsum -= boutsum;

                stackstart = stackpointer - radius + div;
                sir = stack[stackstart % div];

                routsum -= sir[0];
                goutsum -= sir[1];
                boutsum -= sir[2];

                if (x == 0) {
                    vmin[y] = Math.min(y + r1, hm) * w;
                }
                p = x + vmin[y];

                sir[0] = r[p];
                sir[1] = g[p];
                sir[2] = b[p];

                rinsum += sir[0];
                ginsum += sir[1];
                binsum += sir[2];

                rsum += rinsum;
                gsum += ginsum;
                bsum += binsum;

                stackpointer = (stackpointer + 1) % div;
                sir = stack[stackpointer];

                routsum += sir[0];
                goutsum += sir[1];
                boutsum += sir[2];

                rinsum -= sir[0];
                ginsum -= sir[1];
                binsum -= sir[2];

                yi += w;
            }
        }

        sentBitmap.setPixels(pix, 0, w, 0, 0, w, h);

        return (sentBitmap);
    }

    /**
     * Scale factor for decrease bitmap size before blur processing.
     * {@link #DEFAULT_SCALE_FACTOR}
     */
    private void setScaleFactor(int scaleFactor) {
        if (scaleFactor < 1) {
            throw new IllegalArgumentException("Scale factor must be >= 1");
        }
        this.scaleFactor = scaleFactor;
    }

    @Override
    protected Bitmap transform(BitmapPool pool, Bitmap toTransform, int outWidth, int outHeight) {
        if (toTransform.getConfig() != Bitmap.Config.ARGB_8888) {
            toTransform = toTransform.copy(Bitmap.Config.ARGB_8888, true);
        }

        Bitmap bitmap = Bitmap.createScaledBitmap(
                toTransform,
                toTransform.getWidth() / scaleFactor,
                toTransform.getHeight() / scaleFactor,
                false
        );
        toTransform.recycle();

        //Add blur to bitmap
        bitmap = getBluredBitmapFastBlur(bitmap, blurRadius / scaleFactor);

        //Add foreground color if needed
        if (foregroundColor > 0) {
            addForegroundColor(bitmap, foregroundColor);
        }

        return bitmap;

    }

    private void addForegroundColor(Bitmap bitmap, @ColorRes int foregroundColor) {
        Canvas canvas = new Canvas(bitmap);
        Paint paint = new Paint();
        paint.setAntiAlias(true);
        paint.setColorFilter(new PorterDuffColorFilter(
                        context.getResources().getColor(foregroundColor),
                        PorterDuff.Mode.SRC_ATOP)
        );
        canvas.drawBitmap(bitmap, 0, 0, paint);
    }

    @Override
    public String getId() {
        return TRANSFORMATION_ID + "(blurRadius = " + blurRadius + ", foreground = " + foregroundColor + ")";
    }
}