On desktop GL, GL 1.5 or GL_ARB_occlusion_query is required to get the
glGenQueries() etc. symbols. This isn’t the case on GLES, where they
are provided by GL_EXT_occlusion_query_boolean, and more importantly
have never been made core.
This patch allows gtk4-demo to start when GDK_DEBUG=gl-gles is set, on
my Mali 400 MP running the Lima driver from Mesa.
Some systems (notably macOS) will not allow enumeration of an extension that has been promoted to core OpenGL for context in use. This change assumes that GL_ARB_timer_query is available on OpenGL 3.3+.
I could not find definitive information on whether GL_ARB_debug_output or GL_KHR_debug have been added to core. Other extensions in use were addressed by https://gitlab.gnome.org/GNOME/gtk/merge_requests/1422 .
usec is the scale of the monotonic timer which is where we get almost
all the times from. The only actual source of nsec is the opengl
GPU time (but who knows what the actual resulution of that is).
Changing this to usec allows us to get rid of " * 1000" in a *lot* of
places all over the codebase, which are ugly and confusing.
