The gl2ext.h header is never supposed to set a define to zero - if you want to override that in your project, you can set it to zero e.g. on the command line. The half float textures are specified as a Khronos extension here http://www.khronos.org/registry/webgl/extensions/OES_texture_half_float/ , and the linear variant at http://www.khronos.org/registry/webgl/extensions/OES_texture_half_float_linear/ , so these do exist.