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cogl: correct check for COGL_OFFSCREEN_DISABLE_DEPTH_AND_STENCIL

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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
This commit is contained in:
Thomas Hindoe Paaboel Andersen 2019-11-15 21:34:12 +01:00
parent 81bb4f0051
commit d992722c24
1 changed files with 1 additions and 1 deletions
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2
cogl/cogl/driver/gl/cogl-framebuffer-gl.c
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@ -865,7 +865,7 @@ _cogl_offscreen_gl_allocate (CoglOffscreen *offscreen,
{
fb->samples_per_pixel = gl_framebuffer->samples_per_pixel;
if (!offscreen->create_flags & COGL_OFFSCREEN_DISABLE_DEPTH_AND_STENCIL)
if (!(offscreen->create_flags & COGL_OFFSCREEN_DISABLE_DEPTH_AND_STENCIL))
{
/* Record that the last set of flags succeeded so that we can
try that set first next time */