Distorted Android

    private TransformFeedback mTF;

      mTF.render();

      mTF = new TransformFeedback(mView.getContext());

///////////////////////////////////////////////////////////////////////////////////////////////////

// Copyright 2016 Leszek Koltunski                                                               //

//                                                                                               //

// This file is part of Distorted.                                                               //

//                                                                                               //

// Distorted is free software: you can redistribute it and/or modify                             //

// it under the terms of the GNU General Public License as published by                          //

// the Free Software Foundation, either version 2 of the License, or                             //

// (at your option) any later version.                                                           //

//                                                                                               //

// Distorted is distributed in the hope that it will be useful,                                  //

// but WITHOUT ANY WARRANTY; without even the implied warranty of                                //

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the                                 //

// GNU General Public License for more details.                                                  //

//                                                                                               //

// You should have received a copy of the GNU General Public License                             //

// along with Distorted.  If not, see <http://www.gnu.org/licenses/>.                            //

///////////////////////////////////////////////////////////////////////////////////////////////////

package org.distorted.examples.feedback;

import android.content.Context;

import android.content.res.Resources;

import android.opengl.GLES30;

import android.util.Log;

import org.distorted.library.Distorted;

import org.distorted.library.program.DistortedProgram;

import java.io.InputStream;

import java.nio.Buffer;

import java.nio.ByteBuffer;

import java.nio.ByteOrder;

import java.nio.FloatBuffer;

///////////////////////////////////////////////////////////////////////////////////////////////////

class TransformFeedback

    {

    private DistortedProgram mFeedbackProgram;

    private int mBufferLength;

    private int[] mVBO, mTBO;

///////////////////////////////////////////////////////////////////////////////////////////////////

    TransformFeedback(final Context context)

        {

        final Resources resources = context.getResources();

        final InputStream vertStream = resources.openRawResource(org.distorted.library.R.raw.feedback_vertex_shader);

        final InputStream fragStream = resources.openRawResource(org.distorted.library.R.raw.feedback_fragment_shader);

        String vertHeader= Distorted.GLSL_VERSION;

        String fragHeader= Distorted.GLSL_VERSION;

        String[] feedback = { "outValue" };

        try

          {

          mFeedbackProgram = new DistortedProgram(vertStream,fragStream, vertHeader, fragHeader, Distorted.GLSL, feedback );

          }

        catch(Exception ex)

          {

          Log.e("TransformFeedback", "exception creating feedback program: "+ex.getMessage());

          }

        float[] floatData = { 2.0f, 4.0f, 9.0f, 16.0f, 25.0f, 100.0f };

        mBufferLength = floatData.length * 4;

        FloatBuffer data = ByteBuffer.allocateDirect(mBufferLength).order(ByteOrder.nativeOrder()).asFloatBuffer();

        data.put(floatData).position(0);

        mVBO = new int[1];

        GLES30.glGenBuffers(1, mVBO, 0);

        GLES30.glBindBuffer(GLES30.GL_ARRAY_BUFFER, mVBO[0]);

        GLES30.glBufferData(GLES30.GL_ARRAY_BUFFER, mBufferLength, data, GLES30.GL_STATIC_READ);

        mTBO = new int[1];

        GLES30.glGenBuffers(1, mTBO, 0);

        GLES30.glBindBuffer(GLES30.GL_TRANSFORM_FEEDBACK_BUFFER, mTBO[0]);

        GLES30.glBufferData(GLES30.GL_TRANSFORM_FEEDBACK_BUFFER, mBufferLength, null, GLES30.GL_STATIC_READ);

        }

///////////////////////////////////////////////////////////////////////////////////////////////////

    void render()

        {

        mFeedbackProgram.useProgram();

        GLES30.glBindBuffer(GLES30.GL_ARRAY_BUFFER, mVBO[0]);

        GLES30.glVertexAttribPointer(mFeedbackProgram.mAttribute[0], 1, GLES30.GL_FLOAT, false, 4, 0);

        GLES30.glBindBufferBase(GLES30.GL_TRANSFORM_FEEDBACK_BUFFER, 0, mTBO[0]);

        GLES30.glEnable(GLES30.GL_RASTERIZER_DISCARD);

        GLES30.glBeginTransformFeedback(GLES30.GL_POINTS);

        GLES30.glDrawArrays(GLES30.GL_POINTS, 0, mBufferLength);

        GLES30.glEndTransformFeedback();

        GLES30.glDisable(GLES30.GL_RASTERIZER_DISCARD);

        GLES30.glFlush();

        Buffer mappedBuffer =  GLES30.glMapBufferRange(GLES30.GL_TRANSFORM_FEEDBACK_BUFFER, 0, mBufferLength, GLES30.GL_MAP_READ_BIT);

        if (mappedBuffer!=null)

            {

            ByteBuffer bb = ((ByteBuffer) mappedBuffer);

            bb.order(ByteOrder.nativeOrder());

            FloatBuffer transformedData = bb.asFloatBuffer();

            Log.d( "TransformFeedback", String.format("output values = %f %f %f %f %f %f\n",

                    transformedData.get(), transformedData.get(), transformedData.get(),

                    transformedData.get(), transformedData.get(), transformedData.get() ));

            }

        GLES30.glUnmapBuffer(GLES30.GL_TRANSFORM_FEEDBACK_BUFFER);

        }

}