[Spice-devel] [vdagent-win PATCH] handle_mouse_event: fix off-by-one when normalizing mouse coordinates

[Fabiano Fidêncio]

On Sun, Nov 22, 2015 at 4:54 PM, Uri Lublin <uril at redhat.com> wrote:
> Mouse coordinates can be 0..(width-1) and 0..(height-1)
>
> Normalization of mouse coordinates (for SendInput) was done
> against w,h and thus right-most and down-most coordinates
> could never be reached.

So, you're avoiding a division by zero, right? This is the main point
of this patch AFAIU.
IMHO, it should be a bit more explicit in the log.

>
> Fix it by normalizing against (w-1) and (h-1).
>
> Also added protection against a case of 0 or 1 (for any of w,h)
> Fixes rhbz#1032037
> ---
>  vdagent/vdagent.cpp | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/vdagent/vdagent.cpp b/vdagent/vdagent.cpp
> index c976665..595db85 100644
> --- a/vdagent/vdagent.cpp
> +++ b/vdagent/vdagent.cpp
> @@ -567,13 +567,15 @@ bool VDAgent::handle_mouse_event(VDAgentMouseState* state)
>      ZeroMemory(&_input, sizeof(INPUT));
>      _input.type = INPUT_MOUSE;
>      if (state->x != _mouse_x || state->y != _mouse_y) {
> +        DWORD w = _desktop_layout->get_total_width();
> +        DWORD h = _desktop_layout->get_total_height();
> +        w = (w > 1) ? w-1 : 1; /* coordinates are 0..w-1, protect w==0 */
> +        h = (h > 1) ? h-1 : 1; /* coordinates are 0..h-1, protect h==0 */
>          _mouse_x = state->x;
>          _mouse_y = state->y;
>          mouse_move = MOUSEEVENTF_MOVE;
> -        _input.mi.dx = (mode->get_pos_x() + _mouse_x) * 0xffff /
> -                       _desktop_layout->get_total_width();
> -        _input.mi.dy = (mode->get_pos_y() + _mouse_y) * 0xffff /
> -                       _desktop_layout->get_total_height();
> +        _input.mi.dx = (mode->get_pos_x() + _mouse_x) * 0xffff / w;
> +        _input.mi.dy = (mode->get_pos_y() + _mouse_y) * 0xffff / h;
>      }
>      if (state->buttons != _buttons_state) {
>          buttons_change = get_buttons_change(_buttons_state, state->buttons, VD_AGENT_LBUTTON_MASK,
> --
> 2.5.0
>
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ACK (feel free to ignore my comment if you think the commit message is
clear enough).

-- 
Fabiano Fidêncio