title: Android OpenGL Render to a frameBuffer in the original (small) resolution and then scale it (viewPort) to the screen size
body: <p>I have a NV21 (YUV420) camera video which I'm applying on it a fragment shader in order to get some filter effects and YUV to RGB convertion as well.
  Everything is working except the bad performance.
  My fragment shader is a bit heavy because it has many <code>textur2D()</code> calls.</p>
  
  <p>The original frame resolution is 480x640 pixels, and I noticed that if I'm setting the viewport to this original size (instead of fullscreen size) it is working good and fluently.</p>
  
  <p>So basically I need first to render the frame and processing it in a frameBuffer (FBO) with that original size and then (after the shader's work done) scale it to the fullscreen size using viewport (1080x1920 mostly), And it means that the "heavy" processing work would be applied on much less fragments.</p>
  
  <p>I've found out some tutorials and similar questions here how to achieve that, but unfortunately I've got no luck with that.  (Got some black screens or GL_INVALID_OPERATION and etc')...
  Any help would be much appreciated.</p>
  
  <p>Also, another (optional) performance tweak that I don't know how to deal with (if it's possible) is to combined somehow these 3 textures (Y_tex, U_tex and V_tex) to a single texture which be uniformed to the shader as a single sampler and then I can make just one <code>texture2D()</code> call in the shader in order to get the current YUV values and convert them to RGB values.</p>
  
  <p>This is my renderer code:</p>
  
  <pre><code>static class MyRenderer implements GLSurfaceView.Renderer
  {
      int mTextureIds[] = new int[3];
      float[] mScaleMatrix = new float[16];
  
      private FloatBuffer mVertexBuffer;
      private FloatBuffer mTextureBuffer;
      private ShortBuffer mDrawListBuffer;
  
      boolean mVideoFitEnabled = true;
      boolean mVideoDisabled = false;
  
      // number of coordinates per vertex in this array
      static final int COORDS_PER_VERTEX = 3;
      static final int TEXTURECOORDS_PER_VERTEX = 2;
  
      static float mXYZCoords[] = {
              -1.0f, 1.0f, 0.0f, // top left
              -1.0f, -1.0f, 0.0f, // bottom left
              1.0f, -1.0f, 0.0f, // bottom right
              1.0f, 1.0f, 0.0f // top right
      };
  
      static float mUVCoords[] = {
              0, 0, // top left
              0, 1, // bottom left
              1, 1, // bottom right
              1, 0  // top right
      };
  
      private short mVertexIndex[] = {0, 1, 2, 0, 2, 3}; // order to draw vertices
  
      private final String vertexShaderCode =
  
                "uniform mat4 uMVPMatrix;"
              + "attribute vec4 aPosition;\n"
              + "attribute vec2 aTextureCoord;\n"
              + "varying vec2 vTextureCoord;\n"
  
              + "void main() {\n"
                  + "  gl_Position = uMVPMatrix * aPosition;\n"
                  + "  vTextureCoord = aTextureCoord;\n"
              + "}\n";
  
  
      private final String fragmentShaderCode =
  
                "precision mediump float;\n"
              + "uniform sampler2D Ytex;\n"
              + "uniform sampler2D Utex,Vtex;\n"
              + "varying vec2 vTextureCoord;\n"
  
              + "void main(void) {\n"
                  + "  float nx,ny,r,g,b,y,u,v;\n"
                  + "  mediump vec4 txl,ux,vx;"
                  + "  nx=vTextureCoord[0];\n"
                  + "  ny=vTextureCoord[1];\n"
  
                  + "  y=texture2D(Ytex,vec2(nx,ny)).r;\n"
                  + "  u=texture2D(Utex,vec2(nx,ny)).r;\n"
                  + "  v=texture2D(Vtex,vec2(nx,ny)).r;\n"
  
                  + "  y=1.1643*(y-0.0625);\n" 
                  + "  u=u-0.5;\n"
                  + "  v=v-0.5;\n"
  
                  + "  r=y+1.5958*v;\n"
                  + "  g=y-0.39173*u-0.81290*v;\n"
                  + "  b=y+2.017*u;\n"
  
                  // --&gt; Bilateral blur filter code HERE &lt;--
  
                  + "  gl_FragColor=vec4(r,g,b,1.0);\n"
              + "}\n";
  
  
  
      ReentrantLock mFrameLock = new ReentrantLock();
      Frame mCurrentFrame;
  
      private int mProgram;
      private int mTextureWidth;
      private int mTextureHeight;
      private int mViewportWidth;
      private int mViewportHeight;
  
      public MyRenderer()
      {
          ByteBuffer bb = ByteBuffer.allocateDirect(mXYZCoords.length * 4);
          bb.order(ByteOrder.nativeOrder());
          mVertexBuffer = bb.asFloatBuffer();
          mVertexBuffer.put(mXYZCoords);
          mVertexBuffer.position(0);
  
          ByteBuffer tb = ByteBuffer.allocateDirect(mUVCoords.length * 4);
          tb.order(ByteOrder.nativeOrder());
          mTextureBuffer = tb.asFloatBuffer();
          mTextureBuffer.put(mUVCoords);
          mTextureBuffer.position(0);
  
          ByteBuffer dlb = ByteBuffer.allocateDirect(mVertexIndex.length * 2);
          dlb.order(ByteOrder.nativeOrder());
          mDrawListBuffer = dlb.asShortBuffer();
          mDrawListBuffer.put(mVertexIndex);
          mDrawListBuffer.position(0);
      }
  
      @Override public void onSurfaceCreated(GL10 gl, EGLConfig config)
      {
          GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
  
          int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);
          int fragmentShader = loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode);
  
          mProgram = GLES20.glCreateProgram(); // create empty OpenGL ES Program
          GLES20.glAttachShader(mProgram, vertexShader); // add the vertex shader to program
          GLES20.glAttachShader(mProgram, fragmentShader); // add the fragment shader to program
          GLES20.glLinkProgram(mProgram);
  
          int positionHandle = GLES20.glGetAttribLocation(mProgram, "aPosition");
          int textureHandle = GLES20.glGetAttribLocation(mProgram, "aTextureCoord");
  
          GLES20.glVertexAttribPointer(positionHandle, COORDS_PER_VERTEX, GLES20.GL_FLOAT, false, COORDS_PER_VERTEX * 4, mVertexBuffer);
          GLES20.glEnableVertexAttribArray(positionHandle);
          GLES20.glVertexAttribPointer(textureHandle, TEXTURECOORDS_PER_VERTEX, GLES20.GL_FLOAT, false, TEXTURECOORDS_PER_VERTEX * 4, mTextureBuffer);
          GLES20.glEnableVertexAttribArray(textureHandle);
          GLES20.glUseProgram(mProgram);
  
          int i = GLES20.glGetUniformLocation(mProgram, "Ytex");                                     //            GLES20.glUniform3i(i, 0, 1, 2);
          GLES20.glUniform1i(i, 0); /* Bind Ytex to texture unit 0 */
  
          i = GLES20.glGetUniformLocation(mProgram, "Utex");
          GLES20.glUniform1i(i, 1); /* Bind Utex to texture unit 1 */
  
          i = GLES20.glGetUniformLocation(mProgram, "Vtex");
          GLES20.glUniform1i(i, 2); /* Bind Vtex to texture unit 2 */
  
          mTextureWidth = 0;
          mTextureHeight = 0;
      }
  
      static void initializeTexture(int name, int id, int width, int height)
      {
          GLES20.glActiveTexture(name);
          GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, id);
          GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_NEAREST);
          GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MAG_FILTER, GLES20.GL_LINEAR);
          GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_S, GLES20.GL_CLAMP_TO_EDGE);
          GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_T, GLES20.GL_CLAMP_TO_EDGE);
          GLES20.glTexImage2D(GLES20.GL_TEXTURE_2D, 0, GLES20.GL_LUMINANCE, width, height, 0, GLES20.GL_LUMINANCE, GLES20.GL_UNSIGNED_BYTE, null);
      }
  
      void setupTextures(Frame frame)
      {
          if (mTextureIds[0] != 0)
          {
              GLES20.glDeleteTextures(3, mTextureIds, 0);
          }
  
          GLES20.glGenTextures(3, mTextureIds, 0);
  
          int w = frame.getWidth();
          int h = frame.getHeight();
          int hw = (w + 1) &gt;&gt; 1;
          int hh = (h + 1) &gt;&gt; 1;
  
          initializeTexture(GLES20.GL_TEXTURE0, mTextureIds[0], w, h);
          initializeTexture(GLES20.GL_TEXTURE1, mTextureIds[1], hw, hh);
          initializeTexture(GLES20.GL_TEXTURE2, mTextureIds[2], hw, hh);
  
          mTextureWidth = frame.getWidth();
          mTextureHeight = frame.getHeight();
      }
  
      void updateTextures(Frame frame)
      {
          int width = frame.getWidth();
          int height = frame.getHeight();
          int half_width = (width + 1) &gt;&gt; 1;
          int half_height = (height + 1) &gt;&gt; 1;
          int y_size = width * height;
          int uv_size = half_width * half_height;
  
          ByteBuffer bb = frame.getBuffer();
          bb.clear();  // If we are reusing this frame, make sure we reset position and limit
  
          if (bb.remaining() == y_size + uv_size * 2)
          {
              bb.position(0);
  
              GLES20.glPixelStorei(GLES20.GL_UNPACK_ALIGNMENT, 1);
              GLES20.glPixelStorei(GLES20.GL_PACK_ALIGNMENT, 1);
  
              GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
              GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, mTextureIds[0]);
              GLES20.glTexSubImage2D(GLES20.GL_TEXTURE_2D, 0, 0, 0, width, height, GLES20.GL_LUMINANCE, GLES20.GL_UNSIGNED_BYTE, bb);
  
              bb.position(y_size);
  
              GLES20.glActiveTexture(GLES20.GL_TEXTURE1);
              GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, mTextureIds[1]);
              GLES20.glTexSubImage2D(GLES20.GL_TEXTURE_2D, 0, 0, 0, half_width, half_height, GLES20.GL_LUMINANCE, GLES20.GL_UNSIGNED_BYTE, bb);
  
              bb.position(y_size + uv_size);
  
              GLES20.glActiveTexture(GLES20.GL_TEXTURE2);
              GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, mTextureIds[2]);
              GLES20.glTexSubImage2D(GLES20.GL_TEXTURE_2D, 0, 0, 0, half_width, half_height, GLES20.GL_LUMINANCE, GLES20.GL_UNSIGNED_BYTE, bb);
  
  
  
              int i = GLES20.glGetUniformLocation(mProgram, "width");
              GLES20.glUniform1f(i, (float) mTextureWidth);
  
              i = GLES20.glGetUniformLocation(mProgram, "height");
              GLES20.glUniform1f(i, (float) mTextureHeight);
          }
  
          else
          {
              mTextureWidth = 0;
              mTextureHeight = 0;
          }
      }
  
      @Override public void onSurfaceChanged(GL10 gl, int width, int height)
      {
          GLES20.glViewport(0, 0, width, height);
          mViewportWidth = width;
          mViewportHeight = height;
      }
  
      @Override public void onDrawFrame(GL10 gl)
      {
          GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
  
          mFrameLock.lock();
  
          if (mCurrentFrame != null &amp;&amp; !mVideoDisabled)
          {
              GLES20.glUseProgram(mProgram);
  
              if (mTextureWidth != mCurrentFrame.getWidth()    ||    mTextureHeight != mCurrentFrame.getHeight())
              {
                  setupTextures(mCurrentFrame);
              }
  
              updateTextures(mCurrentFrame);
  
              Matrix.setIdentityM(mScaleMatrix, 0);
              float scaleX = 1.0f, scaleY = 1.0f;
              float ratio = (float) mCurrentFrame.getWidth() / mCurrentFrame.getHeight();
              float vratio = (float) mViewportWidth / mViewportHeight;
  
              if (mVideoFitEnabled)
              {
                  if (ratio &gt; vratio)
                  {
                      scaleY = vratio / ratio;
                  }
  
                  else
                  {
                      scaleX = ratio / vratio;
                  }
              }
  
              else
              {
                  if (ratio &lt; vratio)
                  {
                      scaleY = vratio / ratio;
                  }
  
                  else
                  {
                      scaleX = ratio / vratio;
                  }
              }
  
              Matrix.scaleM(mScaleMatrix, 0, scaleX * (mCurrentFrame.isMirroredX() ? -1.0f : 1.0f), scaleY, 1);
  
              int mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");
              GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mScaleMatrix, 0);
  
              GLES20.glDrawElements(GLES20.GL_TRIANGLES, mVertexIndex.length, GLES20.GL_UNSIGNED_SHORT, mDrawListBuffer);
          }
  
          mFrameLock.unlock();
      }
  
      public void displayFrame(Frame frame)
      {
          mFrameLock.lock();
          if (this.mCurrentFrame != null)
          {
              this.mCurrentFrame.recycle();
          }
  
          this.mCurrentFrame = frame;
          mFrameLock.unlock();
      }
  
      public static int loadShader(int type, String shaderCode)
      {
          int shader = GLES20.glCreateShader(type);
  
          GLES20.glShaderSource(shader, shaderCode);
          GLES20.glCompileShader(shader);
  
          return shader;
      }
  
      public void disableVideo(boolean b)
      {
          mFrameLock.lock();
  
          mVideoDisabled = b;
  
          if (mVideoDisabled)
          {
              if (this.mCurrentFrame != null)
              {
                  this.mCurrentFrame.recycle();
              }
  
              this.mCurrentFrame = null;
          }
  
          mFrameLock.unlock();
      }
  
      public void enableVideoFit(boolean enableVideoFit)
      {
          mVideoFitEnabled = enableVideoFit;
      }
  }
  </code></pre>