/usr/share/psychtoolbox-3/PsychOneliners/IsGLES.m is in psychtoolbox-3-common 3.0.11.20131230.dfsg1-1build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | function rc = IsGLES
% Returns 1 if active rendering api is OpenGL-ES,
% 0 otherwise.
val = getenv('PSYCH_USE_GFX_BACKEND');
rc = (length(val) >= 4) && strcmp(val(1:4), 'gles');
|