Android: How can you get framebuffer (screenshot) on rooted device?

Question

I tried :

process = Runtime.getRuntime().exec("su -c cat /dev/graphics/fb0 > /sdcard/frame.raw");
process.waitFor();

but it doesn't work. My device is rooted.

I see many answers that it requires rooted access, but no actual code to get the framebuffer.

I also tried glReadPixels() but no luck.

public void TakeScreen() {

        DisplayMetrics dm = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(dm);
        int width = dm.widthPixels;
        int height = dm.heightPixels;

        int screenshotSize = width * height;
        ByteBuffer bb = ByteBuffer.allocateDirect(screenshotSize * 4);
        bb.order(ByteOrder.nativeOrder());
        gl.glReadPixels(0, 0, width, height, GL10.GL_RGBA,
                GL10.GL_UNSIGNED_BYTE, bb);
        int pixelsBuffer[] = new int[screenshotSize];
        bb.asIntBuffer().get(pixelsBuffer);
        bb = null;
        Bitmap bitmap = Bitmap.createBitmap(width, height,
                Bitmap.Config.RGB_565);
        bitmap.setPixels(pixelsBuffer, screenshotSize - width, -width, 0, 0,
                width, height);
        pixelsBuffer = null;

        short sBuffer[] = new short[screenshotSize];
        ShortBuffer sb = ShortBuffer.wrap(sBuffer);
        bitmap.copyPixelsToBuffer(sb);

        for (int i = 0; i < screenshotSize; ++i) {
            short v = sBuffer[i];
            sBuffer[i] = (short) (((v & 0x1f) << 11) | (v & 0x7e0) | ((v & 0xf800) >> 11));
        }
        sb.rewind();
        bitmap.copyPixelsFromBuffer(sb);
        saveBitmap(bitmap, "/screenshots", "capturedImage");
    }

Were you able to this in the end? If so, could you share how? — Zoltán Szőcs, Aug 03 '11 at 15:23
See http://stackoverflow.com/questions/17304611/android-read-fb0-always-give-me-blackscreen/17331970#17331970 — fadden, Aug 26 '13 at 14:35

score 0 · Answer 1 · edited Jun 10 '12 at 07:13

0

The answer lies in replicating the way the device itself handles it:

fb = open("/dev/graphics/fb0", O_RDONLY);

check this

edited Jun 10 '12 at 07:13

swiftBoy

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answered Aug 07 '11 at 02:08

Austin Hanson

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score 0 · Answer 2 · answered Aug 07 '11 at 02:30

Seems to me like your problem is this sign: >. You cannot redirect output using exec. What you need to do is grab the output stream of the process (which is the input stream for you) and store it to file;

process = Runtime.getRuntime().exec("su -c cat /dev/graphics/fb0");
InputStream is = process.getInputStream();
...

Android: How can you get framebuffer (screenshot) on rooted device?

2 Answers2

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