Macro check_for_gl_error

macro_rules! check_for_gl_error {
    ($gl: expr) => { ... };
    ($gl: expr, $context: literal) => { ... };
}

Check for OpenGL error and report it using log::error.

Only active in debug builds!

use egui_glow::check_for_gl_error;
check_for_gl_error!(glow_context);
check_for_gl_error!(glow_context, "during painting");