Linux-driver on Ubuntu 14.04.4/64-bit with card AMD/ATI Richland Radeon HD
8570D
  (AMD Radeon R7 240):

it seems that "glLogicOp (GL_XOR)" does not work:

..
  glLogicOp (GL_XOR);
  glEnable (GL_COLOR_LOGIC_OP);
..
  glPixelZoom (1.f, 1.f);
  glDrawPixels (rb_dx, rb_dy,  // width, height
      // GL_BLUE,  // yellow
      GL_GREEN,    // violet
      // GL_RED,   // cyan
      GL_FLOAT,
      fBuf);                   // data
  glDisable(GL_COLOR_LOGIC_OP);


creates a black background only.

Sourcecode: see function GL_RubberBox_draw in:
https://github.com/gcad3d/gcad3d/blob/master/src/gr/ut_GL.c

The proprietary AMD/ATI-driver and all Nvidia-cards/drivers work ok with this
code.

---------------------------------------------------------
CAD-CAM Services Ing. Franz Reiter
email franz.reiter@cadcam.co.at
http://www.cadcam.co.at
http://www.gcad3d.org
---------------------------------------------------------