The viewport is lost

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In my render() method, I set a viewport:

Gdx.gl.glViewport((int)viewport.x, (int)viewport.y,(int)viewport.width 
(int)viewport.height);

But when i run rayHandler.updateAndRender(), my viewport is lost. This problem 
only appear on the OpenGL20. When i "excavate" the source code, I found out the 
cause:

Gdx.gl.glBlendFunc(GL20.GL_SRC_ALPHA, GL20.GL_ONE);

This method causes the loss of viewport, but i don't know how to restore 
viewport?

Original issue reported on code.google.com by hunghd...@gmail.com on 25 Oct 2013 at 2:37

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[deleted comment]

[GoogleCodeExporter]

Actually it is the problem of libgdx FrameBuffer class, see -> 
  /** Makes the frame buffer current so everything gets drawn to it. */
  public void begin () {
    Gdx.graphics.getGL20().glViewport(0, 0, colorTexture.getWidth(), ColorTexture.getHeight());
    Gdx.graphics.getGL20().glBindFramebuffer(GL20.GL_FRAMEBUFFER, framebufferHandle);
  }

  /** Unbinds the framebuffer, all drawing will be performed to the normal   framebuffer from here on. */
  public void end () {
    Gdx.graphics.getGL20().glViewport(0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
    Gdx.graphics.getGL20().glBindFramebuffer(GL20.GL_FRAMEBUFFER, 0);
  }

It doesn't restore your previous viewport.

To fix it you can create new constructor for RayHandler and LightMap acquiring 
your viewport and then restoring it in:
RayHandler.java:
  void renderWithShaders() {
    ...
    if (shadows || blur) {
      lightMap.frameBuffer.end();           
      // RESTORE VIEWPORT after lightMap FBO used
      Gdx.gl.glViewport(viewport.x, viewport.y, viewport.width, viewport.height);
      lightMap.render();
    }
  }
and in LightMap.java:
  public void gaussianBlur() {
    ...
    Gdx.gl20.glEnable(GL20.GL_BLEND);
    // RESTORE VIEWPORT after blur FBO used
    Gdx.gl.glViewport(viewport.x, viewport.y, viewport.width, viewport.height); 
  }

Original comment by mihail.churbanov@gmail.com on 3 Dec 2013 at 10:50

[GoogleCodeExporter]

Or you can acquire viewport automatically before the first call to FBO.begin() 
using glGetIntegerv with GL_VIEWPORT flag. And restore it as I wrote in 
previous post.

Original comment by mihail.churbanov@gmail.com on 3 Dec 2013 at 10:53

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I'm going to report this issue to libgdx and possibly make a fork so that 
box2dlights wouldn't need changed to make it work.

Original comment by mihail.churbanov@gmail.com on 3 Dec 2013 at 11:07