In _cogl_offscreen_gl_allocate we only want to perform certain actions if
COGL_OFFSCREEN_DISABLE_DEPTH_AND_STENCIL is not set in create_flags.
We perfrom this check with:
if (!offscreen->create_flags & COGL_OFFSCREEN_DISABLE_DEPTH_AND_STENCIL)
which is not correct as we negate the create_flags before the bitwise &.
It happens to work as intended though, as CoglOffscreenFlags only has one
element, and that element has the value 1. If the flag is not set then the
nagation of create_flags is true and the bitwise and with the element value
is true as well.
If any flag is set then the negation will give 0 and the bitwise & will be
false.
So while it works correctly it is fragile as either additional flags or a
change in the enum element value will break this check. This patch makes
things a bit more safe by adding parentheses to let the bitwise & happen
before the negation.
Definition of the enum:
typedef enum
{
COGL_OFFSCREEN_DISABLE_DEPTH_AND_STENCIL = 1
} CoglOffscreenFlags;
https://gitlab.gnome.org/GNOME/mutter/merge_requests/938
d992722c24