USER-CENTERED DESIGN OF GPU-BASED SHADER PROGRAMS Topics: Graphical Interfaces; Graphics in Computer Games; Lighting and Appearance; Real-Time Graphics; Real-Time Rendering; Reflection and Illumination Models; Systems and Software Architectures for Rendering In Proceedings of the International Conference on Computer Graphics Theory and Applications and International Conference on Information Visualization Theory and Applications - Volume 0VISIGRAPP, 248-253, 2012 , Rome, Italy