Cargo Features

[dependencies]
luminance-gl = { version = "0.19.1", default-features = false, features = ["gl33", "GL_ARB_gpu_shader_fp64"] }
default = gl33

The gl33 feature is set by default whenever luminance-gl is added without default-features = false somewhere in the dependency tree.

gl33 default
GL_ARB_gpu_shader_fp64

OpenGL extensions