Complex sentence: While at Silicon Graphics Inc. Mark authored the OpenGL Utility Toolkit, better known as GLUT, to make it easy to write OpenGL-based 3D examples and demos, the primary reason for this was the lack of a windowing and input API with OpenGL using GLX.
Split into simpler sentences: While at Silicon Graphics, he authored the OpenGL Utility Toolkit, better known as GLUT, to make it easy to write OpenGL-based 3D examples and demos. The primary reason for this was the lack of a windowing and input API with OpenGL using GLX.