[Mesa-dev] [PATCH 2/7] egl/x11: check for dri2_dpy->flush before using the flush extension

[Chad Versace]

On Mon 15 May 2017, Emil Velikov wrote:
> From: Emil Velikov <emil.velikov at collabora.com>
> 
> Analogous to previous commit.
> 
> Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
> ---

> If people prefer I can split the whitespace/indent changes in 
> this/previous path from the rest. Don't feel too strongly either way.

I do think the patches would be easier to review if you did that. As
written, it's difficult to see what's behavioral change vs cosmetic
cleanups.

> 
>  src/egl/drivers/dri2/platform_x11.c | 22 +++++++++-------------
>  1 file changed, 9 insertions(+), 13 deletions(-)
> 
> diff --git a/src/egl/drivers/dri2/platform_x11.c b/src/egl/drivers/dri2/platform_x11.c
> index 3bce0bb3f21..becf00547e6 100644
> --- a/src/egl/drivers/dri2/platform_x11.c
> +++ b/src/egl/drivers/dri2/platform_x11.c
> @@ -817,8 +817,7 @@ dri2_copy_region(_EGLDriver *drv, _EGLDisplay *disp,
>     if (draw->Type == EGL_PIXMAP_BIT || draw->Type == EGL_PBUFFER_BIT)
>        return EGL_TRUE;
>  
> -   if (dri2_dpy->flush)
> -      dri2_dpy->flush->flush(dri2_surf->dri_drawable);
> +   dri2_dpy->flush->flush(dri2_surf->dri_drawable);
>  
>     if (dri2_surf->have_fake_front)
>        render_attachment = XCB_DRI2_ATTACHMENT_BUFFER_FAKE_FRONT_LEFT;
> @@ -880,8 +879,7 @@ dri2_x11_swap_buffers_msc(_EGLDriver *drv, _EGLDisplay *disp, _EGLSurface *draw,
>      * happened.  The driver should still be using the viewport hack to catch
>      * window resizes.
>      */
> -   if (dri2_dpy->flush &&
> -       dri2_dpy->flush->base.version >= 3 && dri2_dpy->flush->invalidate)
> +   if (dri2_dpy->flush->base.version >= 3 && dri2_dpy->flush->invalidate)
>        dri2_dpy->flush->invalidate(dri2_surf->dri_drawable);
>  
>     return swap_count;
> @@ -893,19 +891,17 @@ dri2_x11_swap_buffers(_EGLDriver *drv, _EGLDisplay *disp, _EGLSurface *draw)
>     struct dri2_egl_display *dri2_dpy = dri2_egl_display(disp);
>     struct dri2_egl_surface *dri2_surf = dri2_egl_surface(draw);
>  
> -   if (dri2_dpy->dri2) {
> -      if (dri2_x11_swap_buffers_msc(drv, disp, draw, 0, 0, 0) != -1) {
> -          return EGL_TRUE;
> -      }
> +   if (!dri2_dpy->flush) {
> +      dri2_dpy->core->swapBuffers(dri2_surf->dri_drawable);
> +      return EGL_TRUE;

Yes, thank you.

I'll say it again to anyone who's reading. The Go style guide insists on
this, for good reason.

    https://github.com/golang/go/wiki/CodeReviewComments#indent-error-flow

    Try to keep the normal code path at a minimal indentation, and indent
    the error handling, dealing with it first. This improves the readability
    of the code by permitting visually scanning the normal path quickly.

> +   }
> +
> +   if (dri2_x11_swap_buffers_msc(drv, disp, draw, 0, 0, 0) == -1) {
>        /* Swap failed with a window drawable. */
>        _eglError(EGL_BAD_NATIVE_WINDOW, __func__);
>        return EGL_FALSE;
> -   } else {
> -      assert(dri2_dpy->swrast);
> -
> -      dri2_dpy->core->swapBuffers(dri2_surf->dri_drawable);
> -      return EGL_TRUE;
>     }
> +   return EGL_TRUE;
>  }

There's a lot of hidden complexity in platform_x11.c, and I'm unsure if
this patch preserves proper extension checks. I defer to someone who
knows this code better.