mupdf: android library: How to invert the colors or change to night mode

Question

If anyone using mupdf library for android know how to invert the background. I want to add a button to the ui

Answer 1

It's very simple. In PageView while rendering bitmap just invert the bitmap.

mEntire.setImageBitmap(invert(mEntireBm));
mPatch.setImageBitmap(invert(mPatchBm));

Here is how you can invert a bitmap.

    private Bitmap invert(Bitmap src) {
        int height = src.getHeight();
        int width = src.getWidth();

        Bitmap bitmap = Bitmap.createBitmap(width, height, src.getConfig());
        Canvas canvas = new Canvas(bitmap);
        Paint paint = new Paint();

        ColorMatrix matrixGrayscale = new ColorMatrix();
        matrixGrayscale.setSaturation(0);

        ColorMatrix matrixInvert = new ColorMatrix();
        matrixInvert.set(new float[]
                {
                        -1.0f, 0.0f, 0.0f, 0.0f, 255.0f,
                        0.0f, -1.0f, 0.0f, 0.0f, 255.0f,
                        0.0f, 0.0f, -1.0f, 0.0f, 255.0f,
                        0.0f, 0.0f, 0.0f, 1.0f, 0.0f
                });
        matrixInvert.preConcat(matrixGrayscale);

        ColorMatrixColorFilter filter = new ColorMatrixColorFilter(matrixInvert);
        paint.setColorFilter(filter);

        canvas.drawBitmap(src, 0, 0, paint);
        // src.recycle();
        return bitmap;
    }