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Screenshot from camera takes too much time

November 28, 2017 - 8:19am #1

Hi everyone,

I'm using the Vuforia SDK for Android and it works perfectly. I'm able to take a screenshot of the GLSurfaceView (for image analysis with opencv algorithms) and it works fine on device with small screens (I've plugged this in my surface's view GLSurfaceView.Renderer

DisplayMetrics dm = new DisplayMetrics();


            int w = dm.widthPixels;

            int h = dm.heightPixels;

            int b[] = new int[w * (y + h)];

            int bt[] = new int[w * h];

            IntBuffer ib = IntBuffer.wrap(b);


            //gl.glReadPixels(x, 0, w, y + h, GL10.GL_RGBA, GL10.GL_UNSIGNED_BYTE, ib);

            GLES20.glReadPixels(0, 0, w, h, GLES20.GL_RGBA, GLES20.GL_UNSIGNED_BYTE, ib);

            for (int i = 0, k = 0; i < h; i++, k++) {//remember, that OpenGL bitmap is incompatible with Android bitmap

                //and so, some correction need.

                for (int j = 0; j < w; j++) {

                    int pix = b[i * w + j];

                    int pb = (pix >> 16) & 0xff;

                    int pr = (pix << 16) & 0x00ff0000;

                    int pix1 = (pix & 0xff00ff00) | pr | pb;

                    bt[(h - k - 1) * w + j] = pix1;



            Bitmap screnshot = Bitmap.createBitmap(bt, w, h, Bitmap.Config.ARGB_8888);


However, when dealing with high-resolution screens and camera this causes a 20ms freeze in the camera rendering. I've tried to make this call asynchronously but then I obtain a black screenshot. I also tried to copy the camera in a buffer and then read pixel from this buffer but the freeze remains : 

final int frameIdIndex=0,renderIdIndex=1,textureIdIndex=2;

            final int[] bufferId=new int[3];

            // bind renderbuffer and create a 16-bit depth buffer

            // width and height of renderbuffer = width and height of

            // the texture

            GLES20.glBindRenderbuffer(GLES20.GL_RENDERBUFFER, bufferId[renderIdIndex]);


            //bind the frameBuffer;


            //specify texture as color attachment


            //specify renderbuffer as depth_attachment


            //check for framebuffer complete

            int status= GLES20.glCheckFramebufferStatus(GLES20.GL_FRAMEBUFFER);

            if(status !=GLES20.GL_FRAMEBUFFER_COMPLETE) {

                throw new RuntimeException("status:"+status+", hex:"+Integer.toHexString(status));


            final int screenshotSize = width * height;

            final ByteBuffer bb = ByteBuffer.allocateDirect(screenshotSize * 4);


            GLES20.glReadPixels(0, 0, width, height, GLES20.GL_RGBA,

            GL10.GL_UNSIGNED_BYTE, bb);

            int pixelsBuffer[] = new int[screenshotSize];


            final Bitmap bitmap = Bitmap.createBitmap(width, height,


            bitmap.setPixels(pixelsBuffer, screenshotSize - width, -width,

                    0, 0, width, height);

            pixelsBuffer = null;

            short sBuffer[] = new short[screenshotSize];

            ShortBuffer sb = ShortBuffer.wrap(sBuffer);


            // Making created bitmap (from OpenGL points) compatible with

            // Android

            // bitmap

            for (int i = 0; i < screenshotSize; ++i) {

                short v = sBuffer[i];

                sBuffer[i] = (short) (((v & 0x1f) << 11) | (v & 0x7e0) | ((v & 0xf800) >> 11));




            // cleanup

            GLES20.glDeleteRenderbuffers(1, bufferId,renderIdIndex);

            GLES20.glDeleteFramebuffers(1, bufferId ,frameIdIndex);

            GLES20.glDeleteTextures(1, bufferId,textureIdIndex);

I've also tried to register a preview callback on my Android camera but then OpenGLSurfaceView does not display the camera anymore

mCamera.setOneShotPreviewCallback(new Camera.PreviewCallback() {


            public void onPreviewFrame(byte[] bytes, Camera camera) {     

                    DisplayMetrics dm = new DisplayMetrics();

                    Bitmap screenshot = BitmapFactory.decodeByteArray(bytes, 0, bytes.length);




I've also tried to modify the surfaceholder view : mGLView.getHolder().setFixedSized(width, height) but then it "zooms in" my image instead of scaling it. I then tried to use mGLView.setScaleX() and setScaleY() to but it back on but without success.

And I also tried Renderer.getInstance().setVideoBackgroundConfig(config) to change the resolution but then I got a tiny video area that I do not manage to scale.


Does anyone know how to take a screenshot asynchrounously without causing performance loss ? 

Best regards

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