[PATCH xserver 1/2] randr: rrCheckPixmapBounding: Do not substract crtc non 0 x, y from screen size

[Dave Airlie]

On 23 November 2016 at 00:28, Hans de Goede <hdegoede at redhat.com> wrote:
> The purpose of rrCheckPixmapBounding is to make sure that the
> screen_pixmap is large enough for the slave-output which crtc is
> being configured.
>
> This should include crtc->x and crtc->y, otherwise the crtc might
> still end up scanning out an area outside of the screen-pixmap.
>
> For example: Take a laptop with an external monitor on a slave-output at
> 1920x1080+0+0 and its internal-screen at 3840x2160+1920+0 and in
> gnome-settings-daemon move the external monitor to be on the ri ght of
> the internal screen rather then on the left. First g-s-d will do a
> RRSetScreenSize to 5760*2160 (which is a nop), then it calls RRSetCrtc
> to move the slave output to 1920x1080+3840+0, since this is a slave
> output, rrCheckPixmapBounding gets called, since the 2 crtcs now overlap
> the code before this commit would shrinks the screen_pixmap to 3180*2160.
> Then g-s-d calls RRSetCrtc to move the internal screen to 3180*2160+0+0.
>
> And we end up with the slave-output configured to scan-out an area
> which completely falls outside of the screen-pixmap (and end up with
> a black display on the external monitor).
>
> This commit fixes this by not substracting the x1 and y1 coordinates
> of the union-ed region when determining the new screen_pixmap size.
>
> Cc: Nikhil Mahale <nmahale at nvidia.com>
> Cc: Dave Airlie <airlied at redhat.com>
> Signed-off-by: Hans de Goede <hdegoede at redhat.com>

Thanks Hans, these seems to make sense to me.

Reviewed-by: Dave Airlie <airlied at redhat.com>

> ---
>  randr/rrcrtc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/randr/rrcrtc.c b/randr/rrcrtc.c
> index 5d404e8..ac853ea 100644
> --- a/randr/rrcrtc.c
> +++ b/randr/rrcrtc.c
> @@ -686,8 +686,8 @@ rrCheckPixmapBounding(ScreenPtr pScreen,
>      }
>
>      newsize = RegionExtents(&total_region);
> -    new_width = newsize->x2 - newsize->x1;
> -    new_height = newsize->y2 - newsize->y1;
> +    new_width = newsize->x2;
> +    new_height = newsize->y2;
>
>      if (new_width == screen_pixmap->drawable.width &&
>          new_height == screen_pixmap->drawable.height) {
> --
> 2.9.3
>
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